Copyright 2001 Psychonomic Society Inc 336

Animal Learning amp Behavior2001 29 (4) 336-353

Fish live in a medium that is an especially good conduc-tor of sound and the myriad extant speciesmdashsome 25000in the class Osteichthyes (bony fishes) alone (Nelson1984)mdashhave evolved diverse mechanisms for transducingacoustic stimuli It should not be surprising if sophisticatedfunctionality in the auditory domain turns out to be amajor component of the perceptual and cognitive capabil-ities of fish

This paperrsquos point of departure is the elegant study byPorter and Neuringer (1984) which demonstrated the hith-erto unsuspected capability of pigeons to classify musicinto stylistic categories just as humans do My interest intesting koi on a similar task evolved into the present seriesof experiments which range over the areas of discrimina-tion learning categorization reversal learning and musicperception and which indicate the existence of hitherto un-suspected capabilities in fish

Like Porter and Neuringer (1984) I prefer to optimizethe chance of discovering currently unknown capabilitiesin an animal by seeking a positive result in a top-downfashion first challenging the subject with a task complexenough to require such capabilities and then simplifyingonly as necessary The current understanding of fish psy-choacoustics does nothing to discourage high expectationsof fishesrsquo higher perceptual functions In the case of per-haps the most extensively studied species ldquoabsolute detec-tion thresholds frequency discrimination intensity discrim-

ination temporal summation complex spectrum discrim-ination temporal discrimination and resolution and vari-ous measures of lsquoauditory filterrsquo characteristics show thatthe goldfish falls solidly within a general vertebrate pat-tern of auditory processingrdquo (Fay amp Ream 1986 p 1883)Furthermore goldfish are known to perceive acoustic di-mensions equivalent to what humans perceive as pitch andtimbre (Fay 1995) Indeed for more than a decade it hasseemed clear that humans and animals share the basic psy-choacoustic functions and that there are probably no fun-damental qualitative differences in auditory perception be-tween humans and at least those fish whose anatomy allowsthem to hear reasonably well (Fay 1992 1994 1995 1998Jacobs amp Tavolga 1968 Popper amp Fay 1993 PopperPlatt amp Saidel 1982)

The present subjects were koi which are members ofthe carp family and close relatives of the goldfish Neithergoldfish nor koi are known to communicate by makingsounds (Fay 1995) but both are classified as otophysansa group that has bony structures (the Weberian ossicles)coupling the swim bladder to the inner ears in which thereare hair cells with a specialized orientation pattern Be-cause of this anatomy carp are among the species referredto as hearing specialists which have the greatest auditorybandwidth and sensitivity of any fish (Popper amp Fay 1993)Figure 1 shows the frequency sensitivity range of koi incomparison with the spectral ranges of other animals andof music Their relatively low upper limit of hearing meansthat koi would hear music roughly as it would sound to usover an ordinary voice-grade telephone line

In one of the more complex experiments in fish psy-choacoustics Fay (1992) conditioned goldfish to a two-tonechord and then tested them on a range of individual pitchesobtaining essentially a bimodal generalization curve whosepeaks corresponded to the component pitches of the train-ing chord Thereby Fay was the first to demonstrate analyticlistening (Hartman 1988) in a nonhuman animalmdashin thiscase the ability to discriminate the individual components

This work was supported by the Rowland Institute for Science Igratefully acknowledge the help of Winfield Hill for instrumentationprogramming and encouragement I thank Dan Coutu for the MIDImusic and Matt Maltzman for ongoing discussions and help with themanuscript Thank you Angel Peterchev for suggesting Paganinirsquostheme for the melody experiment Thanks are due Chris Stokes and theRowland Staff Special thanks to Allen Neuringer for his inspiration andinvaluable comments Correspondence concerning this article should beaddressed to A R Chase Rowland Institute for Science 100 EdwinLand Boulevard Cambridge MA 02142 (e-mail chaserowlandorg)

Music discriminations by carp (Cyprinus carpio)

AVA R CHASERowland Institute for Science Cambridge Massachusetts

Studies using three koi (Cyprinus carpio) investigated discrimination of musical stimuli The com-mon protocol used a single manipulandum and a multiple continuous reinforcement-extinction sched-ule signaled by music of the S+ and S types in 30-sec presentations separated by a silent 15-sec in-tertrial interval In a categorization study the fish learned to discriminate blues recordings fromclassical generalizing from John Lee Hooker (guitar and vocals) and Bach (oboe concertos) to multi-ple artists and ensembles A control-by-reversal test developed into a demonstration of progressive im-provement in iterated reversal learning The subjects next learned to discriminate single-timbre syn-thesized versions of similar music In the final study which used melodies with the same order ofnote-duration values but with mirror-image orders of pitch values one fish discriminated melodieswith no timbre cues in contrast to results reported in rats

MUSIC DISCRIMINATIONS BY CARP 337

of a compound stimulus consisting of simultaneous tonesor pulse trains (Fay 1992 1998) Although perhaps complexby psychophysical standards however even these stimulidid not embody any large-scale pattern or structure thatwould challenge or demonstrate a listenerrsquos higher mentalfunctions

Porter and Neuringer (1984) pioneered a dramatic way tobegin exploring the connections between psychoacousticsand cognition Music has become an important kind ofstimulus in comparative psychology because of its excita-tion of fundamental cognitive functions the accessibilityof its perceptual dimensions (pitch timbre tempo etc)and its analytically tractable internal structures (Hulse ampPage 1988) Little is known about the correspondence be-tween the elements of music the units of perception andthe stimulus-feature attending hierarchies (Baron 1965Segal amp Harrison 1978)mdashthat is the various stimulus di-mensions to which different species preferentially attendI felt that a demonstration that fish could learn to catego-rize stimuli as complex as music according to a criterionas unnatural as musical genre not only would show thatthey extract meaningful signals but also might suggest acapability for higher order auditory processing compara-ble with that of pigeons and people

GENERAL METHOD

SubjectsThe subjects in all the experiments were 3 pet store koi (Cyprinus

carpio) named Beauty Oro and Pepi By the start of the work re-ported here they had been living together and serving as experi-mental subjects for 5 years and they ranged in age from 7 to 11 yearsand in size from 29 to 36 cm (snout to base of tail) In a prior studyof sensory reinforcement all 3 had had extensive exposure to sev-

eral kinds of music including the blues and classical genres and evento some of the actual recordings that they would learn to actively dis-criminate in the present series of experiments Beauty had alsolearned a visual categorization task in a two-operandum procedure

On average the fish received a collective maintenance ration con-sisting primarily of about 20 grams of Hikari pellets (Kyorin FoodInd Ltd) every weekday On experiment days each animal also typ-ically consumed a gram of 20-mg reinforcement pellets during thesession the maintenance ration was given only after the dayrsquos ex-perimentation

ApparatusThe fish apparatus was novel and was developed in my labora-

tory Its rationale design and construction have been described indetail elsewhere (Chase amp Hill 1999) During experimental ses-sions the home aquarium was divided by a clear partition into an ex-perimental chamber and a holding area and the noisy aeration sys-tem was turned off There were no special provisions for visual oracoustic isolation indeed visual isolation from the shoal was foundto impede performance Auditory stimuli were fed from either oftwo computer-controlled SCSI (small computer system interface)compact disc (CD) players to an underwater speaker The S+ CDwas loaded into one drive and the S CD into the other Compres-sion circuitry (DBX Professional Products Model dbx 163X) madestimuli from the two sources sound equally loud A 200-Hz eighth-order high-pass filter was available to provide the option of reduc-ing possible lateral-line stimulation in fish by removing music fre-quencies lower than 200 Hz in which this sensory system is mostresponsive (Coombs Jannsen amp Montgomer y 1992) The tanksetup is illustrated in Figure 2 The operandum was a horizontal but-ton positioned at the bottom of the tank in front of the speaker A cir-cular puck made of plastic and buoyant foam was the buttonrsquos onlymoving part Designed to be pressed downward by a fish and to berestored by buoyancy alone the puck floated horizontally beneaththe overhanging rim of the cylindrical housing To respond a fishhad to swim down into the cylinder and push the puck with its snoutThe puck was translucent and through it a responding fish could seean internal light source that provided feedback that a response had

Middle C

-20

0

10

20

30

40

50

60

100 1000 104 105

Freq(Hz)

Rats

Humans

Telephone

Pigeons

Carp

SP

L in

dB

Figure 1 Hearing sensitivity threshold curve averages for various an-imals (Fay 1988) sound pressure level (SPL) versus frequency The SPLin water is adjusted by 33 dB with respect to air A high SPL level in-dicates reduced sensitivity at that frequency The animals are carp (Sig-mond amp Wolff 1973 in Fay 1988) rats (Kelly amp Masterton 1980 inFay 1988) humans (Sivian amp White 1933 in Fay 1988) and pigeons(Goerdel-Leich amp Schwartzkopff 1984 in Fay 1988) The relative at-tenuation with frequency of typical analog phone lines in Houston TX(Garfield Houston Area League of PC Users httpwww houstontxusinternetdialupshtml) is shown for comparison as is a piano keyboard(middle C = 256 Hz)

338 CHASE

been registered The unconditioned reinforcer was food in the formof 20 mg-sinking pellets (Noyes formula JG) The pellets weredropped by an automatic feeder (Gerbrands G5120 or MED [Geor-gia VT] Model ENV 203-20) into a plastic tube that terminated un-derwater in an infantrsquos Stage One nipple (Johnson amp Johnson Skill-man NJ) that had been modified to let fish suck the pellets out Theinstantaneous conditioned reinforcer was an external light that back-lit the nipple A computer controlled the experiment and sessionswere videotaped

Preliminary PhaseThe processes of magazine training and of familiarization with

the response button the stimulus presentation system and the restof the apparatus are described in detail in Chase and Hill (1999) Be-fore conducting the genre discrimination experiment it was neces-sary to test the novel apparatus and the intended discrimination pro-tocol For example one objective was to verify that the new horizonta lresponse button did not artificially inflate response rates either bybeing intrinsically reinforcing or by eliciting instinctive mouthingthat could be mistaken for a discriminative response

The subjects were given a simple discrimination taskmdashnamelysound versus silencemdashwhich is described in detail in Chase and Hill(1999) The procedure presented randomly timed intervals (typicallybetween 40 and 90 sec) of music (S+) and silence (S ) in alternationand reinforced each response that was made in the presence of musicwith food To ensure that the onset of music would never reinforcea response made in silence any response made within 20 sec beforethe scheduled end of a silent interval prolonged the silence by reset-ting the countdown timer to 20 sec The reinforcement schedule wasmultiple continuous reinforcement-extinction (CRF-extinction)mdashthat is while music was playing every response was reinforced witha food pellet and during silence no response was reinforced A ses-sion ended with the S+ trial in which the 50th reinforcement wasdispensed

Because CRF provides informational feedback on every responsea subject could ldquofakerdquo a sound discrimination at least in the senseof exhibiting an appropriate response rate differential merely by

sampling and discriminating the prevailing reinforcing contingencyHowever if a fish suppressed responding substantially more in thepresence of one kind of stimulus than in the presence of the other itwould be clear that the fish was not routinely sampling the buttonand thus that it was under the control of the sound As is shown inFigure 3 Beauty and Oro met this standard within the first few ses-sions The characteristically hyperactive Pepi went 13 sessions be-fore his first S trial during which he did not respond at all butotherwise from the start he was much like the other subjects in ex-hibiting downward trends in the average number of responses perS trial and in the percentage of his total responses that occurredduring S (Chase amp Hill 1999)

In Figure 3 and in all other graphs of results the session axis de-notes experimental workdays in each of which a single set of stim-uli was used with all subjects that ran that day Every workday is in-dicated on every subjectrsquos session axis but an individual subjectrsquosstatistics are based on his actual runs only Skipped sessions wererare and were caused by anomalous conditions that either preventedan animalrsquos participation outright or else threatened to render mean-ingless any data that might be taken The fact that the results wereanalyzed in terms of within-subjects comparisons renders immater-ial such fine-grained differences between the experiences of differ-ent subjects

The final function of the sound-versus-silence task was to accus-tom the subjects to responding in the presence of the music that theywould later hear as the first S+ in the genre discrimination task andtherefore all of the sound stimuli were taken from John Lee Hook-errsquos Blues Before Sunrise CD The hope was that this preparationwould facilitate the acquisition of the musicndashmusic discrimination

EXPERIMENT 1Discrimination and Categorization Based on

Musical Genre

In this experiment it was asked whether fish can learnto discriminate between two stylistically different musical

Figure 2 Working end of the experimental tank as seen by the video camera (not shown) includes a parti-tion (P at the silicone joints) a filter (F) a tank tray (T) a gravel bed (G) a speaker (S) a response button (B)a light (L the conditioned reinforcer) which shines through a light-diffusing mylar (M) onto a nipple (N) a pel-let dispenser (D) and an LED (O) which shows the camera that the computer has registered a response FromldquoReliable Operant Apparatus for Fish Audio Stimulus Generator Response Button and Pellet-Dispensing Nipplerdquo by A R Chase and W Hill 1999 Behavior Research Methods Instruments amp Computers 31 p 471Copyright 1999 by the Psychonomic Society Reprinted with permission

MUSIC DISCRIMINATIONS BY CARP 339

stimuli and if so whether they can generalize to unfamiliarmusic from the same stylistic categories capabilities pre-viously demonstrated in pigeons by Porter and Neuringer(1984)

A standard demonstration of categorization behaviorbegins by training an animal to classify the members oftwo nonoverlapping sets of stimuli by responding only inthe presence of the members of one particular set Each setis an experimenter-defined category and each stimulus isan exemplar of one category The animal is said to havelearned the two categories if it then responds appropriatelyto novel exemplars of each and if there is reason to believethat it can also discriminate exemplars within each set aswell as between sets The latter criterion ensures that theanimal was perceiving categories rather than exhibitingcategorical perception that is the animalrsquos treating cer-tain exemplars alike must not be due merely to an inabil-ity to tell them apart (Herrnstein 1992 Sturdy PhillmorePrice amp Weisman 1999)

In visual categorization studies pigeons have beentrained to classify photographs according to whether theydo or do not contain people water fish aerial views of aparticular location tree leaves damaged by a particularspecies of caterpillar and other such complex criteria (Herrn-stein 1992) If intermittent reinforcement is used partic-ular exemplars might be repeated yet never associatedwith reinforcement if there is improvement in the accu-racy of classification of even these stimuli it is reason-able to conclude that the animal is responding to them onthe basis of features that imply membership in a specificcategory instead of as isolated stimuli The training setscan range from closed and repetitive stimuli with testingdone by using novel stimuli as probes to streams of con-tinually novel stimuli in which case classification accu-racy measures categorization behavior on an ongoingbasismdasheven under CRFmdashbecause rote memory (at leastof whole stimuli as opposed to features) can play no role(Malott amp Siddall 1972)

Categories can also be defined with no systematic rela-tionship to stimulus properties so that the only way to dis-

tinguish them is through rote memory of the reinforce-ment contingency associated with each exemplar Rotememory capacity in animals can be considerable Vaughanand Greene (1984) trained pigeons to sort visual imagesinto rote categories and found that they could easily mem-orize hundreds of pictures and remember them for at least2 years In foraging and food-hiding birds such as theHawaiian honeycreeper and Clarkrsquos nutcracker estimatesof the memory capacity for locations range well into thethousands (Herrnstein 1992)

The protocol in the present study used closed trainingsets and CRF but within-session repetition was almostnonexistent The first presentation of a pair of novel CDsconstituted a stream of novel stimuli and served as a mea-surement probe

Because of the prevailing skepticism that koi could dem-onstrate the capabilities I was hoping to find I tried to makeevery task as easy as possible for the animals a constraintthat dictated some procedural choices that might be re-garded as unconventional One example is the use of a freeoperant and CRF rather than discrete trials or a lean rein-forcement schedule Another is the use of reversals in-stead of extinction trials in order to demonstrate control bystimuli rather than by prevailing reinforcement contin-gency The rationale for CRF was to minimize stress andmaximize feedback given that the exertional cost of but-tonpressing appeared relatively high and that consequentlythe maximum possible response rate was expected to berelatively low Unlike a discrete-trials procedure the free-operant approach fixed each trialrsquos stimulus presentationtime while letting the numbers of responses and reinforce-ments vary My intention was to minimize interferencewith the formation of associations between the positivestimulus and the instantaneous conditioned reinforce-ment or the actual consumption of food With respect toelucidating the stimulus control I was concerned that aswitch to total extinction might cause excessive emotionalside effects and reduce the subjectsrsquo long-term viabilityTherefore in my experiments the usual role of extinctiontrials was played by reversals In a study with so few sub-

0

50

100

0 10 20 30 40

Beauty

S+

S-

Tri

als

wit

h N

o P

ress

0 10 20 30 40

Oro

S+

S-

0 10 20 30 40 Session Number

Pepi

S+

S-

Session NumberSession Number

Figure 3 Preliminary phase (sound vs silence) percentages of S+ and S intervals in which the fish did not press the button at allA comparatively high percentage of nonresponding for S indicates successful discrimination Crosses denote silence

340 CHASE

jects reversals can also act like counterbalancing in con-trolling for possible differences in familiarity and saliencywith respect to the stimuli designated as S+ or S Re-versals have the further advantage of offering glimpses ofadditional phenomenamdashin particular reversal learningper se

MethodThe protocol was an extension of that used in the preliminary

sound-versus-silence discrimination as described above Howevernow there were three kinds of intervalsmdashnamely S+ trials (bluesmusic) S trials (classical music) and a silent intertrial interval(ITI) Also the intervals were now of fixed duration 30 sec for S+and S sound trials and 15 sec for the ITI During the ITI a cor-rection procedure was programmed so that any response that oc-curred less than 10 sec before the silence was scheduled to end pro-longed the ITI by resetting the countdown timer to 10 sec Thesequence of S+ and S trials was randomized in real time but a ses-sion always began with two successive S+ trials and there could beno more than three consecutive trials with any one stimulus type Asession ended at the end of the full S+ interval during which the 50threinforcement was delivered

An important aspect of the procedure was that the computer didnot restart the piece of music at the beginning of each trial but in-stead resumed the CD where it had left off (unless there were fewerthan 30 sec of music remaining on that track in which case the stim-ulus would be the first 30 sec of the following track the intent beingto try to ensure that every stimulus would be a full 30 sec of music)Each of the S+ and S CDs contained roughly 120 distinct excerpts and a session ended with the S+ excerpt during which the 50th re-sponse was made so it was rare for a session to run long enough forany CD to start over and thus there was relatively little within-session repetition of stimuli Each excerpt was effectively a separatemini-piece in one of the two styles represented by the two CDsThus even within a single piece of music or CD track what the fishconfronted was essentially a categorization problem in contrast to adiscrimination between two brief musical fragments that would berepeated identically many times in each session Because the com-puter consistently divided a CD into the same sequence of fixed-length excerpts each time a musical CD was somewhat analogousto a tray containing 120 photographic slides as a source of exem-plars in a visual categorization experiment

Figure 4 summarizes the sequence of experimental conditions andthe recordings used starting with the preliminary sound-versus -silence phase The computer software allowed individual tracks to bemarked for exclusion and as is noted in the CD reference list intwo of the blues CDs certain tracks were excluded because they con-tained speech or silence

In the beginning of Experiment 1 (Sessions 40ndash55) the stimulussources were two entire CDs S+ was John Lee Hookerrsquos Blues Be-fore Sunrise (carried over from the sound-versus-silence discrimina-tion) and S was Bach oboe concertos (familiar from a priorstudy) Over the course of the first 6 sessions 2 fish showed no ev-idence of learning the discrimination whereas the 3rd achieved asuccess that proved short-lived Therefore I simplified the task byrestricting the stimuli to a single track from each CD The first suchpair of tracks was used for 30 sessions and over the next 15 sessionsthree new pairs of tracks were used each pair for 5 consecutive ses-sions After the animals had learned to discriminate a single classi-cal track from a single blues track these four times I again allowedthe stimuli to come from the entire CD of each genre

Because CRF was always in effect during S+ providing feedbackas well as reinforcement the best way to reveal whether the fish wereclassifying the music on the basis of a categorical principle ratherthan on the basis of rote memory was to present novel stimuli There-fore scattered throughout the experiment were nine probe sessions in

which both the S+ and the S CDs were novel These were Sessions115 120 131 138 152 157 163 168 and 177 The music was se-lected for diversity within the genre S+ included four different per-formersrsquo CDs plus five compilation CDs with more than 20 addi-tional blues performers S consisted of six baroque-style CDs andthree non-baroque composersmdashspecifically Mozart Beethovenand Schubert

The buttonpressing response involves a fishrsquos entire body sincethe fish must position itself over the button and essentially ram itTherefore such a response is inherently somewhat slowmdashfar slowerthan for example a birdrsquos peck at a key or a ratrsquos press of a lever Be-cause the fish typically would not hover over the button and becausethey appeared to commit to a response by swimming in from a dis-tance after each S+ interval the silent ITI began with a grace periodof 1 sec during which a buttonpress would still be counted and re-inforced on the assumption that the response had begun during S+

During Sessions 147ndash149 the 200-Hz high-pass filter was turnedon in order to minimize stimulation of the lateral line The idea wasto try to ensure that the discrimination between blues and classicalwould be made on the basis of input from the fishrsquos inner ears thesensory system presumably most capable of detecting the f ine-grained acoustic features of music that form the basis for stylisticdistinctions by humans

The possibility of acoustic artifacts owing to hardware was testedby a control procedure in which the blues and the classical CDs wereeach loaded into the drive programmed for the other (Sessions 182ndash238) The effect was to reverse the definitions of S+ and S (ie toreinforce responses to classical music but not to blues) This was ex-pected to produce a dramatic decrement in accuracy which woulddemonstrate that responding had indeed been under the control ofthe musical content of the S+ and S channels

Results and DiscussionThe use of CRF imposed the obligation to verify that

the subjects were discriminating the stimuli and notmerely the current state of the multiple CRF-extinctionschedule Proof that a subject was not being cued by feed-back from routine test responses would be a statisticallysignificant difference between the percentages of S andS+ trials in which the subject did not press the button atall Such a finding would allow rejection of the hypothe-sis that the subject had been testing the button equally dur-ing both stimulus conditions The alternative hypothesis isdirectional in that beyond exhibiting a difference per sean auditorily discriminating subject would be expected toignore the response button more during S than during S+Therefore unless otherwise specified throughout thispaper significance is reported in terms of the p value of aone-tailed paired t test (Microsoft Excel 97 SR-1) on thenonresponse percentages associated with the two stimulustypes in each of n sessions the alpha level used was 05

As is indicated graphically in Figures 5 and 6 all 3 koidiscriminated blues from classical music and this behav-ior generalized into an ability to classify unfamiliar ex-emplars by genre [for each of the 3 subjects 9 probe ses-sions t(8) gt 10 p lt 001] To my knowledge this is thefirst demonstration in fish of open-ended categorization(Herrnstein 1992) and of any kind of categorization withauditory stimuli

Figure 5 shows the percentages of S+ and S trials inwhich there was no responding In Session 115 the firstprobe Beauty responded only during S+ and not at all dur-

MUSIC DISCRIMINATIONS BY CARP 341

ing S or ITI In Probe Session 138 the novel S was Vi-valdi guitar music which proved to raise problems Figure 6shows all the responses for each session note the higherS response rate at Session 138 Session 182 was the first

control-by-reversal session Sessions 138 and 182 are fur-ther discussed below

The data from the probe sessions are plotted in Figure 7and are shown in historical context in Figure 5 Figure 7

Figure 4 Experiments 1 and 2 (categorization and iterated reversals) stimulus chart Each column representsa single stimulus CD which is identified by text that starts in that column at the bottom of the figure Each rowrepresents a group of sessions Bullets indicate the CDs presented in their entirety as the S+ and S in each ses-sion group whereas the numbers associated with Sessions 56ndash100 identify the specific CD tracks used as stim-uli A triple bullet marks the first presentation of a given CD a single bullet denotes a stimulus heard previ-ously Rows in which both stimuli are represented by triple bullets denote groups of sessions in which the firstone exposed the subject to all-novel stimuli and thus served as a probe session

342 CHASE

also shows means for the nonprobe and the probe sessionsin the session range 115ndash181 The fish classified musicwith which they had had no training about as accurately asthey classified familiar training stimuli This generaliza-tion to unfamiliar exemplars demonstrates that the fishwere not relying on rote memory but were instead exhibit-ing open-ended categorization (Herrnstein 1992)

To assess whether the fish were exhibiting true percep-tion of categories preclusion of categorical perception(ie the inability to discriminate exemplars within a cat-egory) was necessary The great complexity of musicalstimuli renders likely the existence of a mix of feature di-mensions on the basis of which a sample only a few sec-onds long suffices to distinguish any two pieces or evendifferent performances of the same piece The blues stim-uli ranged from John Lee Hooker to Sonny Boy William-son and the classical ranged from baroque to Schubertboth categories featured a variety of ensembles It is im-plausible that recordings that sound so very different tohumans would be completely indistinguishable to thesefish The result of Experiment 4 below provides strongadditional evidence Koi can discriminate generically simi-lar melodies which implies that they can discriminategenerically similar recordings that differ along a multi-plicity of dimensions of which melody is only one

In Figures 5 and 6 the data for Sessions 182ndash192 showthe disruption of performance following the reversal of thereinforcement contingencies This reversal served as acontrol procedure the result of which confirmed that re-sponding was indeed under the control of the musical con-tent as opposed to any electronic artifact in the S+ andS audio channels

In Sessions 138ndash144 the fish had unexpected difficultydiscriminating Vivaldi guitar concertos from a blues com-pilation Although it is plausible that the fish could havelearned that guitar sounds were characteristic of blues theguitar concertos arguably did not sound to humans as muchlike blues as like the Vivaldi cello concerto which was theprevious S and which the fish had had no trouble dis-tinguishing from blues Another possible source of confu-sion for the f ish was the fact that this S+ was the firstcompilation CD to be presented as a stimulus Thus the di-versity of blues styles distinguished this S+ CD from anyprevious one Given the fishesrsquo problem with this dis-crimination I paired the Vivaldi guitar concertos with somevery familiar John Lee Hooker (Sessions 145ndash146) Whendiscrimination did not improve I left these stimuli in placebut turned on the 200-Hz high-pass filter for three ses-sions (147ndash149) As can be seen from Figure 5 the resultof turning on the filter was an immediate improvement inperformance which persisted after the filter was turnedoff Apparently these particular stimuli were salient andhad similar features in the lower frequencies which con-fused the fish until the high-pass filter forced them to at-tend to higher frequency features on the basis of whichthe music was more readily discriminable It would alsoappear that the lateral line was not necessary for the dis-crimination of familiar music As DrsquoAmato and Salmon

(1982) noted ldquoIndividuals do not always rely on the sameproperty of the stimulus and may according to circum-stances shift their reliance from one feature to anotherrdquo(p 130) (In any case Vivaldi evidently can impress listen-ers in odd ways Porter amp Neuringer 1984 reported thata Vivaldi violin concerto sounded more like Stravinsky thanlike Bach to their pigeons as it did also to some humans)

Even a convincing demonstration of categorization canfail to identify the stimulus features that exert control atany given time especially if the stimuli are complex In par-ticular there can be uncertainty as to whether classificationbehavior had been under the stimulus control of the fea-tures in terms of which the experimenter had defined thecategories or whether the subjects had discovered an ef-fective discriminant of which the experimenter was unawareThe diversity of S+S pairings (see Figure 4) presum-ably rules out the possibility that the fish could have beenrelying on only a single discriminant such as timbre buta constant concern is the possible existence of a simple at-tribute that would have allowed the subjects merely to dis-criminate instead of categorizing In the present experi-ment the choices of stimuli and control procedures wereintended to ensure that all the available discriminants weresufficiently complex For example even if a fish used asthe discriminant the sound of a human voice which waspresent in virtually all of the blues but in none of the clas-sical the diversity of singing voices would imply open-ended categorization nonetheless

The possibility that the fish memorized individual or re-curring features cannot be ruled out An animal probablydoes exploit a collection of memorized features alongwith various abstracted properties It would be surprisingif no features at all were salient enough to be rememberedand one wonders whether it is even possible to abstract acategorical discriminant without having particular fea-tures in memory at least temporarily

The notion that koi might classify blues and classicalmusic on the basis of deeper generic attributes is supportedby the results of experiments reported below which indi-cate that timbre cues are not required Porter and Neuringer(1984) trained pigeons to discriminate baroque from mod-ern music using initial exemplars that could have been al-ternatively classified as organ and orchestral music but theeffective discriminant turned out to be something otherthan instrumental timbre In a recent report (Watanabe ampSato 1999) Java sparrows learned to discriminate pianomusic by Schoumlnberg from piano music by Bach and theythen correctly classified orchestral music as Schoumlnberg-like or Bach-like whether written by those two composersor by Carter and (even) Vivaldi Studies that analyze the per-ceptual world of pigeons in terms of multidimensionalscaling spaces reveal that the birds learn enough aboutnonexemplars to form a distinct category for them as wellas for exemplars In other words pigeons appear to eval-uate a stimulus not only as possibly a good exemplar but alsoas a good nonexemplar which is more work than binaryclassification logically requires (Herrnstein 1994) Giventhat the more features of the environment to which one is

MUSIC DISCRIMINATIONS BY CARP 343

sensitive the more information is available from which todiscern patterns and changes indications that animalslearn more than the minimal solution to classificationproblems involving complex stimuli suggest that as com-pared with trying to ignore as much as possible of theworld evolution favors embracing its complexity

EXPERIMENT 2 Iterated Reversals

MethodThe first categorization session in which the contingencies were

reversed had served as a control procedure This experimental con-

0

25

50

75

100

Tri

als

wit

h N

o P

ress

Beauty

S-

S+

0

25

50

75

100

Tri

als

wit

h N

o P

ress

Oro

S-

S+

200 Hz filter

0

25

50

75

100

Tri

als

wit

h N

o P

ress

40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

Session Number

Pepi

S+

S-

S+ S- ITI

Figure 5 Experiment 1 (categorization) percentages of S+ (blues) and S (classical) trials and intertrial intervals (ITIs silence)during which the fish did not press the button at all plotted for each session The greater the separation between a sessionrsquos S+ andS nonresponse percentages the more clearly the subject was discriminating the stimuli as opposed to responding indiscriminatelyand receiving feedback from the reinforcement contingency The boxed data points indicate probe sessions The bar from Sessions147ndash149 shows where the 200-Hz low-frequency cutoff filter was used The circled data points (Session 182) indicate the first control-by-reversal session In the reversal sessions (182ndash192) S+ (still represented by open squares) was now classical music whereas S (stillrepresented by filled triangles) was blues Crosses denote silence

344 CHASE

dition (ie with blues now the S and classical now the S+) wasthen extended into an iterated-reversal experiment The primary goalwas to test koi in reversal learning with complex auditory stimuliafter having found nothing in the literature on the subject of auditoryreversal learning in fish

A secondary goal was to prepare for a planned experiment with aclassification procedure involving two visually distinct buttons withresponses on a particular button to be reinforced only in the presenceof a particular type of music The rim of the original button had beenmachined from black Delrin A new rim was made from an ivory-

colored blank of the same plastic and installed after six sessions ofthe unsignaled reversal (ie no change in the button) Thereafterrim color alternated in synchrony with contingency reversals withblack and ivory signaling that S+ was blues and classical respec-tively The fish would experience a total of four color changes thefirst of which did not signal a contingency change

The sessions were terminated by either the trial in which the 50thpellet was dispensed or an elapsed time of 90 min whichever camefirst Altogether there were 119 sessions spanning four reversals(see Figure 4)

Figure 6 Experiment 1 (categorization) all responses Number of responses in each session during blues trials classical trials andintertrial intervals (ITIs) Under the reversal condition that began with Session 182 blues became S and classical became S+ Bluesresponse counts above 50 reflect the onset of extinction Reversal sessions in which the classical response count was less than 50 wereterminated at 90 min Crosses denote silence

0

20

40

60

80

100

120

All

Pre

sses

40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

Session Number

Pepi

0

20

40

60

80

100

120

All

Pre

sses

ITI

Oro

0

20

40

60

80

100

120

All

Pre

sses

BeautyBluesClassicalITI

MUSIC DISCRIMINATIONS BY CARP 345

Just before the first reversal the stimuli had been a House of Bluescompilation (S+) and a baroque horn compilation (S ) When thecontingencies were reversed making blues S and classical S+both stimuli were also replaced The first reversal stimuli were Bachoboe concertos (S+) and John Lee Hookerrsquos Real Folks Blues (S )both very familiar to the fish In the next three phases of the first re-versal three additional pairs of familiar CDs were used In the fifthand final phase of the first reversal the fish were exposed to entirelynovel stimuli (S The Blues Story compilation S+ Bach triosonatas) As in the categorization study the first session with novelstimuli (Session 224) served as a probe testing for open-ended cat-egorization Blues and classical successively exchanged roles as S+and S in three additional reversal phases all using familiar stim-uli As can be seen in Figure 4 when the first and third reversals oc-curred at least one stimulus CD changed as well The final reversalbrought the contingencies back to where they had been before thefirst reversalmdashnamely with blues as S+ and classical as S

ResultsThe first reversal (Session 182) produced considerable

behavioral disruption and erroneous responding (see Fig-

ures 8 and 9) In the first 6ndash9 sessions the increase in re-sponding to the genre newly become S+ was insufficientfor any fish to earn 50 reinforcements within the 90-mintime limit (Figure 8) Beauty and Oro steadily improvedand were reliably discriminating by the 16th and 23rd ses-sions respectively Pepi achieved significance by Session 9but then his performance was substandard until Session 27[5 sessions ts(4) gt 229 p lt 010 p lt 009 and p lt 042respectively] Near the end of the first reversal the probesession (224) revealed that the classification behavior ex-hibited by Beauty and Oro was clearly open-ended catego-rization With each successive reversal it took fewer sessionsfor Beauty and Oro to demonstrate clear discrimination(Figures 9 and 10) Even Pepi eventually learned each re-versalmdashalbeit while continuing to call attention to the ex-istence of considerable and systematic individual differ-ences among fish In Figure 9 least-squares regressionlines are plotted for S nonresponse data and as is shownin Figure 10 their slopes indicate improvement rates of

0

50

100 Beauty

0

50

100 Oro

0

50

100

Mean 115 120 131 138 152 157 163 168 177 Mean

Probe Sessions (Novel CDs) Probes

Pepi

Non probes

S+S-ITI

Tri

als

wit

h N

o P

ress

Tri

als

wit

h N

o P

ress

Tri

als

wit

h N

o P

res

s

Figure 7 Experiment 1 (categorization) categorization performance during probe ses-sions (ie all-novel stimuli) percentages of S+ trials intertrial intervals (ITI) and S tri-als in which the fish did not respond Black bars indicate S+ gray bars indicate S andwhite bars indicate ITI Low nonresponse percentages for S+ indicate a high likelihoodof responding during S+ whereas high nonresponse percentages for S indicate that thefish tended to ignore the button during S The leftmost ldquoMeanrdquo bars show the averagesof all the nonprobe sessions in the session range 115ndash181 and the rightmost ldquoMeanrdquo barsshow the averages of the probe sessions

346 CHASE

08 and 11 per session for Beauty and Oro respec-tively during the first reversal (Sessions 182ndash238) Overthe final 5 sessions of each reversal phase discriminationby Beauty Oro and Pepi was statistically significant at

levels always better than p lt 010 p lt 016 and p lt 042respectively [ts(4) gt 229] It can be seen in Figure 8 thatwith each reversal the increase in responding to the new S+was generally faster than the extinction to the former S+

0

20

40

60

80

100

120

All

Pre

sses

Beauty

0

20

40

60

80

100

120

All

Pre

sses

Oro

ITI

Session Number

blues

classical classicalbluesblues

0

20

40

60

80

100

120

All

Pre

sses

150 175 200 225 250 275 300

Pepi

classical

BluesClassical

Figure 8 Experiment 2 (iterated reversals) counts of all responses by session Note that in graphs of reversal data the symbols con-sistently indicate genre (open squares blues filled triangles classical) not stimulus semantics (S+ or S ) which of course change ateach reversal This convention highlights the fluctuating response pattern associated with each genre longitudinally as successive re-versals of reinforcement contingency produce disruption and then learning with increasing efficiency The primary session termina-tion trigger was the trial on which the 50th pellet was delivered but in the early sessions of the first reversal no subject made as manyas 50 ldquocorrectrdquo responses to the former S within the session time limit even while responding many more than 50 times without re-inforcement to the former S+ Note that the extinction-induced response frenzy associated with a genrersquos suddenly becoming S de-creases with each reversal Crosses denote silence

MUSIC DISCRIMINATIONS BY CARP 347

EXPERIMENT 3Transition to Synthetic Keyboard Music and

Polyphonic Discrimination with Identical Timbre

The next step was to try to extend the learned classifi-cation of natural music to MIDI (Musical Instrument Dig-

ital Interface) synthesized music in which S+ and Swere not distinguishable by timbre

MethodPretraining After the iterated-reversal experiment the fish re-

mained in the homeexperimental tank from which all the appara-tus had been removed and they were not exposed to music or to anytraining or experimental procedures for a period of 10 months The

Tri

als

wit

h N

o P

ress

0

25

50

75

100

Reversals

Oro

classical

blues

classical

classical

blues

bluesTri

als

wit

h N

o P

ress

0

25

50

75

100

150 200 250 300

Session Number

Pepi

0

25

50

75

100

First Reversal

Beauty

Probe

Tri

als

wit

h N

o P

ress

ITI

BluesClassicalITI

Figure 9 Experiment 2 (iterated reversals) percentages of trials with no responses by session Note the increasingly efficient learn-ing of nonresponding to each former S+ as shown by the increasing slopes of the least-squares regression lines Session 224 (dashedline) was a probe the accurate discrimination of entirely novel stimuli indicates that the fish were performing open-ended catego-rization Crosses denote silence

348 CHASE

work resumed with a reintroduction to the apparatus and protocol asleft off at the end of the fourth and final reversalmdashthat is with S+and S being blues and classical respectively However the fishwere also being prepared to encounter the synthetic stimuli that werebeing created at that time which consisted of a single short piecefrom each genre rather than a collection comparable in duration andvariety with the commercial CDs used previously Therefore in pre-training the stimuli were the same two CDs the subjects had lastheard (see Figure 4 Session 300) but only a single track from eachS was an excerpt from a Bach oboe concerto S+ was the John LeeHooker song ldquoOne Bourbon One Scotch and One Beerrdquo of whicha synthesized version was in the works

Initially Beauty and Oro seemed to manifest effects of the longhiatus in the form of low response rates (not enough to earn 50 pel-lets in a session) and some transient difficulties operating the buttonand taking pellets from the nipple However even allowing for somerelearning and the reduced size of the new stimuli the immediacywith which all 3 subjects exhibited highly accurate discriminationsuggests that the original discrimination training had been retained(compare the leftmost sessions in Figure 11 with the rightmost inFigure 9)

Procedure The new stimuli were musically simplif ied MIDIkeyboard renditions of music of the types the f ish had alreadylearned to classify S+ was the familiar blues song described aboveand S was the unfamiliar Fugue 2 from Book I of Bachrsquos Well-Tempered Clavier To minimize the presence of extraneous cues allthe performances were done by the same musician with the sameequipment (a Kurzweil Model k2000vp keyboard Young Chang Re-search and Development Institute Waltham MA) the same se-quencing software (Studio Vision Pro Version 40 Opcode SystemsNashville TN) and the same settings for volume and for timbre(acoustic piano) Because the new stimuli were so short that theywould repeat after only a few trials rote memory could play a rolein their discrimination and thus the operative level of stimulus con-trol was being allowed to potentially regress from categorization todiscrimination

The initial synthetic stimuli turned out to trigger a deteriorationin classification accuracy (Figure 11 Session 13) It seemed possi-ble that this was an artifact of the musical translation process be-cause even humans had some difficulty recognizing the John LeeHooker song in synthetic form It had gone from bluesy to bouncyits original bass inflections were absent and there was no melodicvoice comparable with that of the singer Therefore at Session 24 Iintroduced a second generation of stimuli S+ remained the samepiece but the performance was somewhat more faithful to themodel The old S (the Bach fugue) had been much shorter than S+and thus had been repeating more often so it was replaced by a syn-

thesized rendition of the f irst movement of Vivaldirsquos ConcertoGrosso in A minor Opus 3 No 6 whose duration more closelymatched that of S+ In addition the timbre of the blues was changedfrom acoustic piano to rock piano thus adding timbre as an availablediscriminant However from Session 47 until the end of the experi-ment S+ and S again had timbre in common specifically rockpiano (starting in Session 47) chiffloot (starting in Session 55) andguitar (starting in Session 62)

ResultsWith the first presentations in a synthetic timbre discrim-

ination accuracy deteriorated (Figure 11 Sessions 13ndash23)perhaps because the first synthetic S+ was not a good enoughexemplar of the blues genre Pepi essentially ceased re-sponding during this time and had to be dropped from thestudy Starting at Session 24 with improved stimuli and adifference in timbre between S+ and S the behavior ofboth remaining subjects immediately changed and there-after their discriminative accuracy improved continually

When S+ and S were again made identical in timbre(Session 47) accurate classification persisted despite aperformance decrement probably related to the loss of asalient cue When the same pair of MIDI sequences waspresented in additional timbres generalization of accurateclassification to the new sounds appeared seamless The datafrom Session 47 and onward demonstrate [Sessions 18ts(17) gt 16 ps lt 001] that koi are capable of discriminat-ing polyphonic music on the basis of features other thanthe timbre of individual tone sources

EXPERIMENT 4 Discrimination of Melodies

Without Timbre Cues

After observing that instrumental timbre seemed not tobe a necessary discriminant in polyphonic music I inves-tigated whether timbre was necessary for koi to discrimi-nate single-voice musicmdashthat is melodies

MethodIn order to familiarize the subjects with the S+ melody and also

in hopes of rehabilitating Pepi this experiment began with severalsessions of collective exposure to a sound-versus-silence contin-gency CRF signaled by the music that would later be the S+ in thesound-versus-sound discrimination alternated with extinction sig-naled by silence In this group pretraining Pepi was observed bothpressing the button and taking pellets from the nipple but when sub-sequently isolated for melody discrimination sessions he consis-tently shied away from the nipple and again had to be dropped as asubject

The stimuli for the melody discrimination experiment (Figure 12)were all derived from the theme from Paganinirsquos 24th Caprice forsolo violin which is perhaps best known from Rachmaninoff rsquosldquoRhapsody on a Theme by Paganinirdquo S+ was the original melody asperformed on the MIDI keyboard S was derived from S+ by usingthe transformation described by Poli and Previde (1991) By using acomputer to modify the MIDI score S+rsquos order of pitches was re-versed whereas its original order of note durations was retained Inother words the first note of S got the duration of S+rsquos first notebut the pitch of S+rsquos last note the second note of S got the durationof S+rsquos second note but the pitch of S+rsquos next-to-last note and so onThis procedure can be thought of as retaining the rhythm track while

0

1

2

3S

lop

e (

ch

ang

ese

ssio

n)

1 2 3 4

Reversal Number

OroBeauty

Pepi

Figure 10 Experiment 2 (iterated reversals) improvementtrends For Beauty and Oro the improvement rate (Figure 9 re-gression line slopes percentage of nonresponse S trials per ses-sion) increases with each reversal

MUSIC DISCRIMINATIONS BY CARP 349

reversing the pitch track The result is two stimuli that are ldquoidenticalwith respect to their mean frequency note duration and rhythm butnoticeably different in their melodic patternsrdquo (Poli amp Previde 1991p 12) Such a pitch-track-reversed melody differs from a completelybackwards melody only in rhythm sacrificing the linkage betweeneach pitch and its original duration in order to preserve the originalsequence of durations per se (If the original melodymdashunlike the

Rachmaninoffmdashhas a palindromic rhythm track the pitch-track -reversed melody and the completely backwards melody are identical)The melodies were recorded using the same MIDI apparatus as thatdescribed above To enhance clarity the tempo was somewhat slowerthan that of the usual piano performance

Over the course of 53 sessions the instrumental timbre alternatedsix times between strings and acoustic piano but in any given ses-

0

25

50

75

100

Tri

als

wit

h N

o P

res

s

S+

ITI

S-

Beauty

0

25

50

75

100

Tri

als

wit

h N

o P

ress

S+

ITI

S-

Oro

Same Timbre Different Timbre Same Timbre

S+S-ITI

Pepi ceased responding

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 Session Number

S+

ITI

S-

Pepi

Figure 11 Experiment 3 (transition to MIDI and timbre study) percentages of S+ and S trials dur-ing which the fish did not press the button During the first 12 sessions the stimuli consisted of a singletrack from each of the two commercial recordings the subjects had last heard 10 months earlier at theconclusion of the iterated-reversal experiment the immediate resumption of accurate discrimination sug-gests long-term memory of training The circled data points (Sessions 13 and 24) indicate the introduc-tion of the first- and second-generation synthetic music From Session 47 until the end of the experimentS+ and S had identical timbre each boxed data point pair indicates the first presentation of a new tim-bre Session 47 rock piano Session 55 chiffloot and Session 62 guitar Crosses denote silence

350 CHASE

sion S+ and S always had the same timbre The discrimination pro-tocol was unchanged from the previous experiments except that thesession termination trigger was raised from 50 to 55 pellets As a pre-liminary test for a possible perceptual invariance (Hulse Takeuchi ampBraaten 1992) S+ was transposed down a fifth in Sessions 51ndash52

After 53 sessions it was discovered that the MIDI technology hadintroduced artifactual differences between S+ and S A musicallyattuned visitor to the lab detected minor variations in note durationsbetween the two stimuli which apparently had resulted from incor-rect handling of the attackndashsustainndashdecay envelopes of S+rsquos recordednotes There also turned out to be subtle volume differences whichwere said to have resulted from the combination of the MIDI scoreediting process and the volume compression function in the digitalaudio tape (DAT) recorder used to create stimulus master tapesThese differences were confirmed by careful examination of thewaveforms using a computer oscilloscope Therefore a second gen-eration of S was created by direct numerical substitution of the S+pitches into the MIDI score in reverse order and by recording a newmaster tape with all volume compression disabled The correctionswere verified by waveform analysis

After eight sessions with the second-generat ion S both S+ andS were shortened by the removal of each onersquos distinctive initial noteand seven sessions later they were further shortened by the removal oftheir remaining initial six and final four notes The purpose of thesestimulus contractions was to look for behavioral disruption that might

indicate that the subject had been discriminating the melodies on thebasis of such local features as the absolute pitch of the initial note

Results and DiscussionBeautyrsquos performance inexplicably deteriorated to the

point where he had to be dropped as a subjectFigures 13 and 14 report the performance of Oro the only

fish to complete the melody experiment The data showthat without timbre cues Oro clearly discriminated betweenthe two melodies [in each stimulus condition (ie second-generation S first-note-removed and both-ends-clipped)5 final sessions t(4) gt 10 p lt 001]

Oro responded more to S+ than to S even in the veryfirst session with melodic stimuli Familiarization with theS+ during pretraining could well have contributed to thisresponse bias perhaps partly because music heard in asound-versus-silence context had consistently become theS+ in a subsequent sound-versus-sound discriminationHowever the MIDI artifacts in the first-generation stim-uli might also have played a role

Session 54 in which the corrected S was introducedmarks a significant reduction of the separation between

Figure 12 Experiment 4 (melody discrimination) musical scores of the normal (S+) and pitch-reversed (S )melodies

MUSIC DISCRIMINATIONS BY CARP 351

the S+ and the S nonresponse percentages [two-tailed two-sample t test assuming unequal variances contrasting themean difference between S and S+ nonresponse per-centages before and after the change 8 observations just be-fore the stimulus change vs 8 observations just after t(11) =277 p lt 019] This implies that the rather subtle artifactsin the original S had indeed been exploited as discrimi-nants

One oddity is the fact that although the stimuli changedsignificantly in Sessions 54 (second-generation S ) and62 (removal of the first note of S+ and S ) in each case

a pronounced anomaly in Ororsquos performance occurred inthe following session

Studies of melody discrimination in animals have oftenfound that the behavior was controlled by local featuressuch as timbre pitch register or the absolute pitch of the ini-tial note rather than by the melodic patterning per se(DrsquoAmato amp Salmon 1984 Hulse amp Cynx 1985 Hulseamp Page 1988 Poli amp Previde 1991) (In this paper for theterm local properties I follow the convention of referringnot only to features like distinctive individual notes whichare clearly local in a temporal sense but also to features

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 70

Session Number

S+

S-

= Piano= Down a fifth= wo 1st note= wo 1st 7 amp last 4 notes

S+S-ITI

Figure 13 Experiment 4 (melody discrimination) trials with no responses The MIDI timbre was violin except for 13 sessions ofpiano as marked The corrected S was introduced at Session 54 The first notes of S+ and S were removed at Session 62 The sixinitial and four final notes were removed at Session 69 Crosses denote silence

Figure 14 Experiment 4 (melody discrimination) all responses Sessions terminated with the S+ trial in which the 55th pel-let was dispensed Crosses denote silence

0

20

40

60

All

Pre

sses

0 10 20 30 40 50 60 70

Session Number

S+

S-

Oro

S+S-ITI

352 CHASE

like timbre and pitch register which although recogniz-able in any local segment can be constant over the dura-tion of the stimulus and which therefore might arguablybe called global properties) It should not be surprisingthat with sequential stimuli such as sound animals oftenexploit local features in preference to global pattern fea-tures In the acoustic domain features that are instantly rec-ognizable presumably confer a survival advantage not onlyon listeners but also on creatures in whose interest it is tobe identifiable by sounds they make Oro did not have tim-bre available as a discriminant but there is no conclusiveevidence that he did or did not use other local features andit is not known which if any global features he might haveused

It warrants mention that in this type of discriminationexperiment inaccurate responding need not imply that thesubject is musically insensitive because musical sensitiv-ity can actually confound discriminative accuracy if bothstimuli are musically plausible or stylistically similar In-deed throughout this experiment the stimuli were moni-tored through a speaker in the laboratory office and S+ andS became so familiar and the pitch-track-reversed Ssounded so pleasing that human observers occasionallybecame confused as to which reinforcement contingencywas in force in the tank

The finding that Oro did not need timbre cues to dis-criminate melodies contrasts sharply with the result in ratsreported by Poli and Previde (1991) Using as stimuli for-ward and pitch-track-reversed versions of the melodyldquoFregravere Jacquesrdquo they tested for discrimination on the basisof melodic pattern The rats had neither previous experi-mental experience nor prior familiarity with music In anattempt to preclude the exploitation of local features suchas the absolute pitch of distinctively positioned notes each15-sec stimulus presentation began at a randomly chosenposition within the melody Different groups of subjectswere asked to discriminate two melodic stimuli that dif-fered in melody only in timbre only or in both attributesHowever the stimuli were never heard as unitary melodiesfrom start to finish and were presented in a continuousstream of randomly sequenced exposures with responsesin the presence of S+ being reinforced only on an FR-5schedule This would seem to be such a formidable task asto make it unsurprising that animals failed except when tim-bre a consistent property of every note in each stimuluswas available as a discriminant However Poli and Previdedid suggest that rats might well prove able to discriminatemelodies without timbre cues under other conditions

CONCLUDING REMARKS

The distinction between local features and pattern fea-tures although it arose in connection with melody dis-crimination is equally relevant to the categorization ex-periment To say that in classifying music as blues orclassical the koi might have been responding to deepgeneric attributes is not to say that they were necessarilyusing anything other than local cues because the diag-

nostic property could have been a particular combinationof timbre loudness pitch brief rhythmic or melodic fig-ures and other such local features A human scanning aradio dial requires only a fraction of a second to identifythe genre of a given station hardly enough time for patternfeatures to manifest themselves so a brief sample of musiccould well contain something recognizable to an animalthat had a rote store of auditory feature memories Localfeatures might control classification behavior even whenthere is extensive exposure to a stimulus Conceivably an-imals could acquire a functional understanding of musicentirely on the basis of the distribution and frequency ofvarious combinations of essentially local features with-out regard to the artistic pattern features in terms of whichmusical genres are commonly defined

Prior to this series of experiments the prevailing opinionappeared to be skepticism as to whether koi could dis-criminate one piece of music from another under any cir-cumstances Now it appears that these animals can discrim-inate polyphonic music discriminate melodic patternsand even classify music by artistic genre As far as I knowthese experiments presented the most complex auditorystimuli to which fish have ever been shown capable ofmaking sophisticated discriminative responses Howeverthere remains the task of elucidating the stimulus controlfunctions of the constituents of that complexity such aspattern features local features and simple properties of thestimulus as a whole The present work was intended as ex-ploratory rather than explanatory and the results clearly ex-tend the known envelope of auditory capabilities in fish

REFERENCES

Baron M R (1965) The stimulus stimulus control and generaliza-tion In D I Mostovsky (Ed) Stimulus generalization (pp 62-71)Stanford CA Stanford University Press

Chase A R amp Hill W (1999) Reliable operant apparatus for fishAudio stimulus generator response button and pellet-dispensing nip-ple Behavior Research Methods Instruments amp Computers 31 470-478

Coombs S Jannsen J amp Montgomery J C (1992) Functional andevolutionary implications of peripheral diversity in lateral line sys-tems In D B Webster R R Fay amp A N Popper (Eds) The evolu-tionary biology of hearing (pp 267-294) New York Springer-Verlag

DrsquoAmato M R amp Salmon D P (1982) Tune discrimination in mon-keys (Cebus apella) and rats Animal Learning amp Behavior 10 126-134

DrsquoAmato M R amp Salmon D P (1984) Processing of complex au-ditory stimuli (tunes) by rats and monkeys (Cebus apella) AnimalLearning amp Behavior 12 184-194

Fay R R (1988) Hearing in vertebrates A psychophysics data-bookWinnetka IL Hill-Fay Associates

Fay R R (1992) Analytic listening in goldfish Hearing Research 59101-107

Fay R R (1994) Perception of temporal acoustic patterns by the gold-fish (Carassius auratus) Hearing Research 76 158-172

Fay R R (1995) Perception of spectrally and temporally complexsounds by the goldfish (Carassius auratus) Hearing Research 89146-154

Fay R R (1998) Auditory stream segregation in goldfish (Carassiusauratus) Hearing Research 120 69-76

Fay R R amp Ream T J (1986) Acoustic response and tuning in sac-cular nerve fibers of the goldfish (Carassius auratus) Journal of theAcoustical Society of America 79 1883-1895

Hartman W M (1988) Pitch perception and the segregation and inte-

MUSIC DISCRIMINATIONS BY CARP 337

of a compound stimulus consisting of simultaneous tonesor pulse trains (Fay 1992 1998) Although perhaps complexby psychophysical standards however even these stimulidid not embody any large-scale pattern or structure thatwould challenge or demonstrate a listenerrsquos higher mentalfunctions

Porter and Neuringer (1984) pioneered a dramatic way tobegin exploring the connections between psychoacousticsand cognition Music has become an important kind ofstimulus in comparative psychology because of its excita-tion of fundamental cognitive functions the accessibilityof its perceptual dimensions (pitch timbre tempo etc)and its analytically tractable internal structures (Hulse ampPage 1988) Little is known about the correspondence be-tween the elements of music the units of perception andthe stimulus-feature attending hierarchies (Baron 1965Segal amp Harrison 1978)mdashthat is the various stimulus di-mensions to which different species preferentially attendI felt that a demonstration that fish could learn to catego-rize stimuli as complex as music according to a criterionas unnatural as musical genre not only would show thatthey extract meaningful signals but also might suggest acapability for higher order auditory processing compara-ble with that of pigeons and people

GENERAL METHOD

SubjectsThe subjects in all the experiments were 3 pet store koi (Cyprinus

carpio) named Beauty Oro and Pepi By the start of the work re-ported here they had been living together and serving as experi-mental subjects for 5 years and they ranged in age from 7 to 11 yearsand in size from 29 to 36 cm (snout to base of tail) In a prior studyof sensory reinforcement all 3 had had extensive exposure to sev-

eral kinds of music including the blues and classical genres and evento some of the actual recordings that they would learn to actively dis-criminate in the present series of experiments Beauty had alsolearned a visual categorization task in a two-operandum procedure

On average the fish received a collective maintenance ration con-sisting primarily of about 20 grams of Hikari pellets (Kyorin FoodInd Ltd) every weekday On experiment days each animal also typ-ically consumed a gram of 20-mg reinforcement pellets during thesession the maintenance ration was given only after the dayrsquos ex-perimentation

ApparatusThe fish apparatus was novel and was developed in my labora-

tory Its rationale design and construction have been described indetail elsewhere (Chase amp Hill 1999) During experimental ses-sions the home aquarium was divided by a clear partition into an ex-perimental chamber and a holding area and the noisy aeration sys-tem was turned off There were no special provisions for visual oracoustic isolation indeed visual isolation from the shoal was foundto impede performance Auditory stimuli were fed from either oftwo computer-controlled SCSI (small computer system interface)compact disc (CD) players to an underwater speaker The S+ CDwas loaded into one drive and the S CD into the other Compres-sion circuitry (DBX Professional Products Model dbx 163X) madestimuli from the two sources sound equally loud A 200-Hz eighth-order high-pass filter was available to provide the option of reduc-ing possible lateral-line stimulation in fish by removing music fre-quencies lower than 200 Hz in which this sensory system is mostresponsive (Coombs Jannsen amp Montgomer y 1992) The tanksetup is illustrated in Figure 2 The operandum was a horizontal but-ton positioned at the bottom of the tank in front of the speaker A cir-cular puck made of plastic and buoyant foam was the buttonrsquos onlymoving part Designed to be pressed downward by a fish and to berestored by buoyancy alone the puck floated horizontally beneaththe overhanging rim of the cylindrical housing To respond a fishhad to swim down into the cylinder and push the puck with its snoutThe puck was translucent and through it a responding fish could seean internal light source that provided feedback that a response had

Middle C

-20

0

10

20

30

40

50

60

100 1000 104 105

Freq(Hz)

Rats

Humans

Telephone

Pigeons

Carp

SP

L in

dB

Figure 1 Hearing sensitivity threshold curve averages for various an-imals (Fay 1988) sound pressure level (SPL) versus frequency The SPLin water is adjusted by 33 dB with respect to air A high SPL level in-dicates reduced sensitivity at that frequency The animals are carp (Sig-mond amp Wolff 1973 in Fay 1988) rats (Kelly amp Masterton 1980 inFay 1988) humans (Sivian amp White 1933 in Fay 1988) and pigeons(Goerdel-Leich amp Schwartzkopff 1984 in Fay 1988) The relative at-tenuation with frequency of typical analog phone lines in Houston TX(Garfield Houston Area League of PC Users httpwww houstontxusinternetdialupshtml) is shown for comparison as is a piano keyboard(middle C = 256 Hz)

338 CHASE

been registered The unconditioned reinforcer was food in the formof 20 mg-sinking pellets (Noyes formula JG) The pellets weredropped by an automatic feeder (Gerbrands G5120 or MED [Geor-gia VT] Model ENV 203-20) into a plastic tube that terminated un-derwater in an infantrsquos Stage One nipple (Johnson amp Johnson Skill-man NJ) that had been modified to let fish suck the pellets out Theinstantaneous conditioned reinforcer was an external light that back-lit the nipple A computer controlled the experiment and sessionswere videotaped

Preliminary PhaseThe processes of magazine training and of familiarization with

the response button the stimulus presentation system and the restof the apparatus are described in detail in Chase and Hill (1999) Be-fore conducting the genre discrimination experiment it was neces-sary to test the novel apparatus and the intended discrimination pro-tocol For example one objective was to verify that the new horizonta lresponse button did not artificially inflate response rates either bybeing intrinsically reinforcing or by eliciting instinctive mouthingthat could be mistaken for a discriminative response

The subjects were given a simple discrimination taskmdashnamelysound versus silencemdashwhich is described in detail in Chase and Hill(1999) The procedure presented randomly timed intervals (typicallybetween 40 and 90 sec) of music (S+) and silence (S ) in alternationand reinforced each response that was made in the presence of musicwith food To ensure that the onset of music would never reinforcea response made in silence any response made within 20 sec beforethe scheduled end of a silent interval prolonged the silence by reset-ting the countdown timer to 20 sec The reinforcement schedule wasmultiple continuous reinforcement-extinction (CRF-extinction)mdashthat is while music was playing every response was reinforced witha food pellet and during silence no response was reinforced A ses-sion ended with the S+ trial in which the 50th reinforcement wasdispensed

Because CRF provides informational feedback on every responsea subject could ldquofakerdquo a sound discrimination at least in the senseof exhibiting an appropriate response rate differential merely by

sampling and discriminating the prevailing reinforcing contingencyHowever if a fish suppressed responding substantially more in thepresence of one kind of stimulus than in the presence of the other itwould be clear that the fish was not routinely sampling the buttonand thus that it was under the control of the sound As is shown inFigure 3 Beauty and Oro met this standard within the first few ses-sions The characteristically hyperactive Pepi went 13 sessions be-fore his first S trial during which he did not respond at all butotherwise from the start he was much like the other subjects in ex-hibiting downward trends in the average number of responses perS trial and in the percentage of his total responses that occurredduring S (Chase amp Hill 1999)

In Figure 3 and in all other graphs of results the session axis de-notes experimental workdays in each of which a single set of stim-uli was used with all subjects that ran that day Every workday is in-dicated on every subjectrsquos session axis but an individual subjectrsquosstatistics are based on his actual runs only Skipped sessions wererare and were caused by anomalous conditions that either preventedan animalrsquos participation outright or else threatened to render mean-ingless any data that might be taken The fact that the results wereanalyzed in terms of within-subjects comparisons renders immater-ial such fine-grained differences between the experiences of differ-ent subjects

The final function of the sound-versus-silence task was to accus-tom the subjects to responding in the presence of the music that theywould later hear as the first S+ in the genre discrimination task andtherefore all of the sound stimuli were taken from John Lee Hook-errsquos Blues Before Sunrise CD The hope was that this preparationwould facilitate the acquisition of the musicndashmusic discrimination

EXPERIMENT 1Discrimination and Categorization Based on

Musical Genre

In this experiment it was asked whether fish can learnto discriminate between two stylistically different musical

Figure 2 Working end of the experimental tank as seen by the video camera (not shown) includes a parti-tion (P at the silicone joints) a filter (F) a tank tray (T) a gravel bed (G) a speaker (S) a response button (B)a light (L the conditioned reinforcer) which shines through a light-diffusing mylar (M) onto a nipple (N) a pel-let dispenser (D) and an LED (O) which shows the camera that the computer has registered a response FromldquoReliable Operant Apparatus for Fish Audio Stimulus Generator Response Button and Pellet-Dispensing Nipplerdquo by A R Chase and W Hill 1999 Behavior Research Methods Instruments amp Computers 31 p 471Copyright 1999 by the Psychonomic Society Reprinted with permission

MUSIC DISCRIMINATIONS BY CARP 339

stimuli and if so whether they can generalize to unfamiliarmusic from the same stylistic categories capabilities pre-viously demonstrated in pigeons by Porter and Neuringer(1984)

A standard demonstration of categorization behaviorbegins by training an animal to classify the members oftwo nonoverlapping sets of stimuli by responding only inthe presence of the members of one particular set Each setis an experimenter-defined category and each stimulus isan exemplar of one category The animal is said to havelearned the two categories if it then responds appropriatelyto novel exemplars of each and if there is reason to believethat it can also discriminate exemplars within each set aswell as between sets The latter criterion ensures that theanimal was perceiving categories rather than exhibitingcategorical perception that is the animalrsquos treating cer-tain exemplars alike must not be due merely to an inabil-ity to tell them apart (Herrnstein 1992 Sturdy PhillmorePrice amp Weisman 1999)

In visual categorization studies pigeons have beentrained to classify photographs according to whether theydo or do not contain people water fish aerial views of aparticular location tree leaves damaged by a particularspecies of caterpillar and other such complex criteria (Herrn-stein 1992) If intermittent reinforcement is used partic-ular exemplars might be repeated yet never associatedwith reinforcement if there is improvement in the accu-racy of classification of even these stimuli it is reason-able to conclude that the animal is responding to them onthe basis of features that imply membership in a specificcategory instead of as isolated stimuli The training setscan range from closed and repetitive stimuli with testingdone by using novel stimuli as probes to streams of con-tinually novel stimuli in which case classification accu-racy measures categorization behavior on an ongoingbasismdasheven under CRFmdashbecause rote memory (at leastof whole stimuli as opposed to features) can play no role(Malott amp Siddall 1972)

Categories can also be defined with no systematic rela-tionship to stimulus properties so that the only way to dis-

tinguish them is through rote memory of the reinforce-ment contingency associated with each exemplar Rotememory capacity in animals can be considerable Vaughanand Greene (1984) trained pigeons to sort visual imagesinto rote categories and found that they could easily mem-orize hundreds of pictures and remember them for at least2 years In foraging and food-hiding birds such as theHawaiian honeycreeper and Clarkrsquos nutcracker estimatesof the memory capacity for locations range well into thethousands (Herrnstein 1992)

The protocol in the present study used closed trainingsets and CRF but within-session repetition was almostnonexistent The first presentation of a pair of novel CDsconstituted a stream of novel stimuli and served as a mea-surement probe

Because of the prevailing skepticism that koi could dem-onstrate the capabilities I was hoping to find I tried to makeevery task as easy as possible for the animals a constraintthat dictated some procedural choices that might be re-garded as unconventional One example is the use of a freeoperant and CRF rather than discrete trials or a lean rein-forcement schedule Another is the use of reversals in-stead of extinction trials in order to demonstrate control bystimuli rather than by prevailing reinforcement contin-gency The rationale for CRF was to minimize stress andmaximize feedback given that the exertional cost of but-tonpressing appeared relatively high and that consequentlythe maximum possible response rate was expected to berelatively low Unlike a discrete-trials procedure the free-operant approach fixed each trialrsquos stimulus presentationtime while letting the numbers of responses and reinforce-ments vary My intention was to minimize interferencewith the formation of associations between the positivestimulus and the instantaneous conditioned reinforce-ment or the actual consumption of food With respect toelucidating the stimulus control I was concerned that aswitch to total extinction might cause excessive emotionalside effects and reduce the subjectsrsquo long-term viabilityTherefore in my experiments the usual role of extinctiontrials was played by reversals In a study with so few sub-

0

50

100

0 10 20 30 40

Beauty

S+

S-

Tri

als

wit

h N

o P

ress

0 10 20 30 40

Oro

S+

S-

0 10 20 30 40 Session Number

Pepi

S+

S-

Session NumberSession Number

Figure 3 Preliminary phase (sound vs silence) percentages of S+ and S intervals in which the fish did not press the button at allA comparatively high percentage of nonresponding for S indicates successful discrimination Crosses denote silence

340 CHASE

jects reversals can also act like counterbalancing in con-trolling for possible differences in familiarity and saliencywith respect to the stimuli designated as S+ or S Re-versals have the further advantage of offering glimpses ofadditional phenomenamdashin particular reversal learningper se

MethodThe protocol was an extension of that used in the preliminary

sound-versus-silence discrimination as described above Howevernow there were three kinds of intervalsmdashnamely S+ trials (bluesmusic) S trials (classical music) and a silent intertrial interval(ITI) Also the intervals were now of fixed duration 30 sec for S+and S sound trials and 15 sec for the ITI During the ITI a cor-rection procedure was programmed so that any response that oc-curred less than 10 sec before the silence was scheduled to end pro-longed the ITI by resetting the countdown timer to 10 sec Thesequence of S+ and S trials was randomized in real time but a ses-sion always began with two successive S+ trials and there could beno more than three consecutive trials with any one stimulus type Asession ended at the end of the full S+ interval during which the 50threinforcement was delivered

An important aspect of the procedure was that the computer didnot restart the piece of music at the beginning of each trial but in-stead resumed the CD where it had left off (unless there were fewerthan 30 sec of music remaining on that track in which case the stim-ulus would be the first 30 sec of the following track the intent beingto try to ensure that every stimulus would be a full 30 sec of music)Each of the S+ and S CDs contained roughly 120 distinct excerpts and a session ended with the S+ excerpt during which the 50th re-sponse was made so it was rare for a session to run long enough forany CD to start over and thus there was relatively little within-session repetition of stimuli Each excerpt was effectively a separatemini-piece in one of the two styles represented by the two CDsThus even within a single piece of music or CD track what the fishconfronted was essentially a categorization problem in contrast to adiscrimination between two brief musical fragments that would berepeated identically many times in each session Because the com-puter consistently divided a CD into the same sequence of fixed-length excerpts each time a musical CD was somewhat analogousto a tray containing 120 photographic slides as a source of exem-plars in a visual categorization experiment

Figure 4 summarizes the sequence of experimental conditions andthe recordings used starting with the preliminary sound-versus -silence phase The computer software allowed individual tracks to bemarked for exclusion and as is noted in the CD reference list intwo of the blues CDs certain tracks were excluded because they con-tained speech or silence

In the beginning of Experiment 1 (Sessions 40ndash55) the stimulussources were two entire CDs S+ was John Lee Hookerrsquos Blues Be-fore Sunrise (carried over from the sound-versus-silence discrimina-tion) and S was Bach oboe concertos (familiar from a priorstudy) Over the course of the first 6 sessions 2 fish showed no ev-idence of learning the discrimination whereas the 3rd achieved asuccess that proved short-lived Therefore I simplified the task byrestricting the stimuli to a single track from each CD The first suchpair of tracks was used for 30 sessions and over the next 15 sessionsthree new pairs of tracks were used each pair for 5 consecutive ses-sions After the animals had learned to discriminate a single classi-cal track from a single blues track these four times I again allowedthe stimuli to come from the entire CD of each genre

Because CRF was always in effect during S+ providing feedbackas well as reinforcement the best way to reveal whether the fish wereclassifying the music on the basis of a categorical principle ratherthan on the basis of rote memory was to present novel stimuli There-fore scattered throughout the experiment were nine probe sessions in

which both the S+ and the S CDs were novel These were Sessions115 120 131 138 152 157 163 168 and 177 The music was se-lected for diversity within the genre S+ included four different per-formersrsquo CDs plus five compilation CDs with more than 20 addi-tional blues performers S consisted of six baroque-style CDs andthree non-baroque composersmdashspecifically Mozart Beethovenand Schubert

The buttonpressing response involves a fishrsquos entire body sincethe fish must position itself over the button and essentially ram itTherefore such a response is inherently somewhat slowmdashfar slowerthan for example a birdrsquos peck at a key or a ratrsquos press of a lever Be-cause the fish typically would not hover over the button and becausethey appeared to commit to a response by swimming in from a dis-tance after each S+ interval the silent ITI began with a grace periodof 1 sec during which a buttonpress would still be counted and re-inforced on the assumption that the response had begun during S+

During Sessions 147ndash149 the 200-Hz high-pass filter was turnedon in order to minimize stimulation of the lateral line The idea wasto try to ensure that the discrimination between blues and classicalwould be made on the basis of input from the fishrsquos inner ears thesensory system presumably most capable of detecting the f ine-grained acoustic features of music that form the basis for stylisticdistinctions by humans

The possibility of acoustic artifacts owing to hardware was testedby a control procedure in which the blues and the classical CDs wereeach loaded into the drive programmed for the other (Sessions 182ndash238) The effect was to reverse the definitions of S+ and S (ie toreinforce responses to classical music but not to blues) This was ex-pected to produce a dramatic decrement in accuracy which woulddemonstrate that responding had indeed been under the control ofthe musical content of the S+ and S channels

Results and DiscussionThe use of CRF imposed the obligation to verify that

the subjects were discriminating the stimuli and notmerely the current state of the multiple CRF-extinctionschedule Proof that a subject was not being cued by feed-back from routine test responses would be a statisticallysignificant difference between the percentages of S andS+ trials in which the subject did not press the button atall Such a finding would allow rejection of the hypothe-sis that the subject had been testing the button equally dur-ing both stimulus conditions The alternative hypothesis isdirectional in that beyond exhibiting a difference per sean auditorily discriminating subject would be expected toignore the response button more during S than during S+Therefore unless otherwise specified throughout thispaper significance is reported in terms of the p value of aone-tailed paired t test (Microsoft Excel 97 SR-1) on thenonresponse percentages associated with the two stimulustypes in each of n sessions the alpha level used was 05

As is indicated graphically in Figures 5 and 6 all 3 koidiscriminated blues from classical music and this behav-ior generalized into an ability to classify unfamiliar ex-emplars by genre [for each of the 3 subjects 9 probe ses-sions t(8) gt 10 p lt 001] To my knowledge this is thefirst demonstration in fish of open-ended categorization(Herrnstein 1992) and of any kind of categorization withauditory stimuli

Figure 5 shows the percentages of S+ and S trials inwhich there was no responding In Session 115 the firstprobe Beauty responded only during S+ and not at all dur-

MUSIC DISCRIMINATIONS BY CARP 341

ing S or ITI In Probe Session 138 the novel S was Vi-valdi guitar music which proved to raise problems Figure 6shows all the responses for each session note the higherS response rate at Session 138 Session 182 was the first

control-by-reversal session Sessions 138 and 182 are fur-ther discussed below

The data from the probe sessions are plotted in Figure 7and are shown in historical context in Figure 5 Figure 7

Figure 4 Experiments 1 and 2 (categorization and iterated reversals) stimulus chart Each column representsa single stimulus CD which is identified by text that starts in that column at the bottom of the figure Each rowrepresents a group of sessions Bullets indicate the CDs presented in their entirety as the S+ and S in each ses-sion group whereas the numbers associated with Sessions 56ndash100 identify the specific CD tracks used as stim-uli A triple bullet marks the first presentation of a given CD a single bullet denotes a stimulus heard previ-ously Rows in which both stimuli are represented by triple bullets denote groups of sessions in which the firstone exposed the subject to all-novel stimuli and thus served as a probe session

342 CHASE

also shows means for the nonprobe and the probe sessionsin the session range 115ndash181 The fish classified musicwith which they had had no training about as accurately asthey classified familiar training stimuli This generaliza-tion to unfamiliar exemplars demonstrates that the fishwere not relying on rote memory but were instead exhibit-ing open-ended categorization (Herrnstein 1992)

To assess whether the fish were exhibiting true percep-tion of categories preclusion of categorical perception(ie the inability to discriminate exemplars within a cat-egory) was necessary The great complexity of musicalstimuli renders likely the existence of a mix of feature di-mensions on the basis of which a sample only a few sec-onds long suffices to distinguish any two pieces or evendifferent performances of the same piece The blues stim-uli ranged from John Lee Hooker to Sonny Boy William-son and the classical ranged from baroque to Schubertboth categories featured a variety of ensembles It is im-plausible that recordings that sound so very different tohumans would be completely indistinguishable to thesefish The result of Experiment 4 below provides strongadditional evidence Koi can discriminate generically simi-lar melodies which implies that they can discriminategenerically similar recordings that differ along a multi-plicity of dimensions of which melody is only one

In Figures 5 and 6 the data for Sessions 182ndash192 showthe disruption of performance following the reversal of thereinforcement contingencies This reversal served as acontrol procedure the result of which confirmed that re-sponding was indeed under the control of the musical con-tent as opposed to any electronic artifact in the S+ andS audio channels

In Sessions 138ndash144 the fish had unexpected difficultydiscriminating Vivaldi guitar concertos from a blues com-pilation Although it is plausible that the fish could havelearned that guitar sounds were characteristic of blues theguitar concertos arguably did not sound to humans as muchlike blues as like the Vivaldi cello concerto which was theprevious S and which the fish had had no trouble dis-tinguishing from blues Another possible source of confu-sion for the f ish was the fact that this S+ was the firstcompilation CD to be presented as a stimulus Thus the di-versity of blues styles distinguished this S+ CD from anyprevious one Given the fishesrsquo problem with this dis-crimination I paired the Vivaldi guitar concertos with somevery familiar John Lee Hooker (Sessions 145ndash146) Whendiscrimination did not improve I left these stimuli in placebut turned on the 200-Hz high-pass filter for three ses-sions (147ndash149) As can be seen from Figure 5 the resultof turning on the filter was an immediate improvement inperformance which persisted after the filter was turnedoff Apparently these particular stimuli were salient andhad similar features in the lower frequencies which con-fused the fish until the high-pass filter forced them to at-tend to higher frequency features on the basis of whichthe music was more readily discriminable It would alsoappear that the lateral line was not necessary for the dis-crimination of familiar music As DrsquoAmato and Salmon

(1982) noted ldquoIndividuals do not always rely on the sameproperty of the stimulus and may according to circum-stances shift their reliance from one feature to anotherrdquo(p 130) (In any case Vivaldi evidently can impress listen-ers in odd ways Porter amp Neuringer 1984 reported thata Vivaldi violin concerto sounded more like Stravinsky thanlike Bach to their pigeons as it did also to some humans)

Even a convincing demonstration of categorization canfail to identify the stimulus features that exert control atany given time especially if the stimuli are complex In par-ticular there can be uncertainty as to whether classificationbehavior had been under the stimulus control of the fea-tures in terms of which the experimenter had defined thecategories or whether the subjects had discovered an ef-fective discriminant of which the experimenter was unawareThe diversity of S+S pairings (see Figure 4) presum-ably rules out the possibility that the fish could have beenrelying on only a single discriminant such as timbre buta constant concern is the possible existence of a simple at-tribute that would have allowed the subjects merely to dis-criminate instead of categorizing In the present experi-ment the choices of stimuli and control procedures wereintended to ensure that all the available discriminants weresufficiently complex For example even if a fish used asthe discriminant the sound of a human voice which waspresent in virtually all of the blues but in none of the clas-sical the diversity of singing voices would imply open-ended categorization nonetheless

The possibility that the fish memorized individual or re-curring features cannot be ruled out An animal probablydoes exploit a collection of memorized features alongwith various abstracted properties It would be surprisingif no features at all were salient enough to be rememberedand one wonders whether it is even possible to abstract acategorical discriminant without having particular fea-tures in memory at least temporarily

The notion that koi might classify blues and classicalmusic on the basis of deeper generic attributes is supportedby the results of experiments reported below which indi-cate that timbre cues are not required Porter and Neuringer(1984) trained pigeons to discriminate baroque from mod-ern music using initial exemplars that could have been al-ternatively classified as organ and orchestral music but theeffective discriminant turned out to be something otherthan instrumental timbre In a recent report (Watanabe ampSato 1999) Java sparrows learned to discriminate pianomusic by Schoumlnberg from piano music by Bach and theythen correctly classified orchestral music as Schoumlnberg-like or Bach-like whether written by those two composersor by Carter and (even) Vivaldi Studies that analyze the per-ceptual world of pigeons in terms of multidimensionalscaling spaces reveal that the birds learn enough aboutnonexemplars to form a distinct category for them as wellas for exemplars In other words pigeons appear to eval-uate a stimulus not only as possibly a good exemplar but alsoas a good nonexemplar which is more work than binaryclassification logically requires (Herrnstein 1994) Giventhat the more features of the environment to which one is

MUSIC DISCRIMINATIONS BY CARP 343

sensitive the more information is available from which todiscern patterns and changes indications that animalslearn more than the minimal solution to classificationproblems involving complex stimuli suggest that as com-pared with trying to ignore as much as possible of theworld evolution favors embracing its complexity

EXPERIMENT 2 Iterated Reversals

MethodThe first categorization session in which the contingencies were

reversed had served as a control procedure This experimental con-

0

25

50

75

100

Tri

als

wit

h N

o P

ress

Beauty

S-

S+

0

25

50

75

100

Tri

als

wit

h N

o P

ress

Oro

S-

S+

200 Hz filter

0

25

50

75

100

Tri

als

wit

h N

o P

ress

40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

Session Number

Pepi

S+

S-

S+ S- ITI

Figure 5 Experiment 1 (categorization) percentages of S+ (blues) and S (classical) trials and intertrial intervals (ITIs silence)during which the fish did not press the button at all plotted for each session The greater the separation between a sessionrsquos S+ andS nonresponse percentages the more clearly the subject was discriminating the stimuli as opposed to responding indiscriminatelyand receiving feedback from the reinforcement contingency The boxed data points indicate probe sessions The bar from Sessions147ndash149 shows where the 200-Hz low-frequency cutoff filter was used The circled data points (Session 182) indicate the first control-by-reversal session In the reversal sessions (182ndash192) S+ (still represented by open squares) was now classical music whereas S (stillrepresented by filled triangles) was blues Crosses denote silence

344 CHASE

dition (ie with blues now the S and classical now the S+) wasthen extended into an iterated-reversal experiment The primary goalwas to test koi in reversal learning with complex auditory stimuliafter having found nothing in the literature on the subject of auditoryreversal learning in fish

A secondary goal was to prepare for a planned experiment with aclassification procedure involving two visually distinct buttons withresponses on a particular button to be reinforced only in the presenceof a particular type of music The rim of the original button had beenmachined from black Delrin A new rim was made from an ivory-

colored blank of the same plastic and installed after six sessions ofthe unsignaled reversal (ie no change in the button) Thereafterrim color alternated in synchrony with contingency reversals withblack and ivory signaling that S+ was blues and classical respec-tively The fish would experience a total of four color changes thefirst of which did not signal a contingency change

The sessions were terminated by either the trial in which the 50thpellet was dispensed or an elapsed time of 90 min whichever camefirst Altogether there were 119 sessions spanning four reversals(see Figure 4)

Figure 6 Experiment 1 (categorization) all responses Number of responses in each session during blues trials classical trials andintertrial intervals (ITIs) Under the reversal condition that began with Session 182 blues became S and classical became S+ Bluesresponse counts above 50 reflect the onset of extinction Reversal sessions in which the classical response count was less than 50 wereterminated at 90 min Crosses denote silence

0

20

40

60

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100

120

All

Pre

sses

40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

Session Number

Pepi

0

20

40

60

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100

120

All

Pre

sses

ITI

Oro

0

20

40

60

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100

120

All

Pre

sses

BeautyBluesClassicalITI

MUSIC DISCRIMINATIONS BY CARP 345

Just before the first reversal the stimuli had been a House of Bluescompilation (S+) and a baroque horn compilation (S ) When thecontingencies were reversed making blues S and classical S+both stimuli were also replaced The first reversal stimuli were Bachoboe concertos (S+) and John Lee Hookerrsquos Real Folks Blues (S )both very familiar to the fish In the next three phases of the first re-versal three additional pairs of familiar CDs were used In the fifthand final phase of the first reversal the fish were exposed to entirelynovel stimuli (S The Blues Story compilation S+ Bach triosonatas) As in the categorization study the first session with novelstimuli (Session 224) served as a probe testing for open-ended cat-egorization Blues and classical successively exchanged roles as S+and S in three additional reversal phases all using familiar stim-uli As can be seen in Figure 4 when the first and third reversals oc-curred at least one stimulus CD changed as well The final reversalbrought the contingencies back to where they had been before thefirst reversalmdashnamely with blues as S+ and classical as S

ResultsThe first reversal (Session 182) produced considerable

behavioral disruption and erroneous responding (see Fig-

ures 8 and 9) In the first 6ndash9 sessions the increase in re-sponding to the genre newly become S+ was insufficientfor any fish to earn 50 reinforcements within the 90-mintime limit (Figure 8) Beauty and Oro steadily improvedand were reliably discriminating by the 16th and 23rd ses-sions respectively Pepi achieved significance by Session 9but then his performance was substandard until Session 27[5 sessions ts(4) gt 229 p lt 010 p lt 009 and p lt 042respectively] Near the end of the first reversal the probesession (224) revealed that the classification behavior ex-hibited by Beauty and Oro was clearly open-ended catego-rization With each successive reversal it took fewer sessionsfor Beauty and Oro to demonstrate clear discrimination(Figures 9 and 10) Even Pepi eventually learned each re-versalmdashalbeit while continuing to call attention to the ex-istence of considerable and systematic individual differ-ences among fish In Figure 9 least-squares regressionlines are plotted for S nonresponse data and as is shownin Figure 10 their slopes indicate improvement rates of

0

50

100 Beauty

0

50

100 Oro

0

50

100

Mean 115 120 131 138 152 157 163 168 177 Mean

Probe Sessions (Novel CDs) Probes

Pepi

Non probes

S+S-ITI

Tri

als

wit

h N

o P

ress

Tri

als

wit

h N

o P

ress

Tri

als

wit

h N

o P

res

s

Figure 7 Experiment 1 (categorization) categorization performance during probe ses-sions (ie all-novel stimuli) percentages of S+ trials intertrial intervals (ITI) and S tri-als in which the fish did not respond Black bars indicate S+ gray bars indicate S andwhite bars indicate ITI Low nonresponse percentages for S+ indicate a high likelihoodof responding during S+ whereas high nonresponse percentages for S indicate that thefish tended to ignore the button during S The leftmost ldquoMeanrdquo bars show the averagesof all the nonprobe sessions in the session range 115ndash181 and the rightmost ldquoMeanrdquo barsshow the averages of the probe sessions

346 CHASE

08 and 11 per session for Beauty and Oro respec-tively during the first reversal (Sessions 182ndash238) Overthe final 5 sessions of each reversal phase discriminationby Beauty Oro and Pepi was statistically significant at

levels always better than p lt 010 p lt 016 and p lt 042respectively [ts(4) gt 229] It can be seen in Figure 8 thatwith each reversal the increase in responding to the new S+was generally faster than the extinction to the former S+

0

20

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80

100

120

All

Pre

sses

Beauty

0

20

40

60

80

100

120

All

Pre

sses

Oro

ITI

Session Number

blues

classical classicalbluesblues

0

20

40

60

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100

120

All

Pre

sses

150 175 200 225 250 275 300

Pepi

classical

BluesClassical

Figure 8 Experiment 2 (iterated reversals) counts of all responses by session Note that in graphs of reversal data the symbols con-sistently indicate genre (open squares blues filled triangles classical) not stimulus semantics (S+ or S ) which of course change ateach reversal This convention highlights the fluctuating response pattern associated with each genre longitudinally as successive re-versals of reinforcement contingency produce disruption and then learning with increasing efficiency The primary session termina-tion trigger was the trial on which the 50th pellet was delivered but in the early sessions of the first reversal no subject made as manyas 50 ldquocorrectrdquo responses to the former S within the session time limit even while responding many more than 50 times without re-inforcement to the former S+ Note that the extinction-induced response frenzy associated with a genrersquos suddenly becoming S de-creases with each reversal Crosses denote silence

MUSIC DISCRIMINATIONS BY CARP 347

EXPERIMENT 3Transition to Synthetic Keyboard Music and

Polyphonic Discrimination with Identical Timbre

The next step was to try to extend the learned classifi-cation of natural music to MIDI (Musical Instrument Dig-

ital Interface) synthesized music in which S+ and Swere not distinguishable by timbre

MethodPretraining After the iterated-reversal experiment the fish re-

mained in the homeexperimental tank from which all the appara-tus had been removed and they were not exposed to music or to anytraining or experimental procedures for a period of 10 months The

Tri

als

wit

h N

o P

ress

0

25

50

75

100

Reversals

Oro

classical

blues

classical

classical

blues

bluesTri

als

wit

h N

o P

ress

0

25

50

75

100

150 200 250 300

Session Number

Pepi

0

25

50

75

100

First Reversal

Beauty

Probe

Tri

als

wit

h N

o P

ress

ITI

BluesClassicalITI

Figure 9 Experiment 2 (iterated reversals) percentages of trials with no responses by session Note the increasingly efficient learn-ing of nonresponding to each former S+ as shown by the increasing slopes of the least-squares regression lines Session 224 (dashedline) was a probe the accurate discrimination of entirely novel stimuli indicates that the fish were performing open-ended catego-rization Crosses denote silence

348 CHASE

work resumed with a reintroduction to the apparatus and protocol asleft off at the end of the fourth and final reversalmdashthat is with S+and S being blues and classical respectively However the fishwere also being prepared to encounter the synthetic stimuli that werebeing created at that time which consisted of a single short piecefrom each genre rather than a collection comparable in duration andvariety with the commercial CDs used previously Therefore in pre-training the stimuli were the same two CDs the subjects had lastheard (see Figure 4 Session 300) but only a single track from eachS was an excerpt from a Bach oboe concerto S+ was the John LeeHooker song ldquoOne Bourbon One Scotch and One Beerrdquo of whicha synthesized version was in the works

Initially Beauty and Oro seemed to manifest effects of the longhiatus in the form of low response rates (not enough to earn 50 pel-lets in a session) and some transient difficulties operating the buttonand taking pellets from the nipple However even allowing for somerelearning and the reduced size of the new stimuli the immediacywith which all 3 subjects exhibited highly accurate discriminationsuggests that the original discrimination training had been retained(compare the leftmost sessions in Figure 11 with the rightmost inFigure 9)

Procedure The new stimuli were musically simplif ied MIDIkeyboard renditions of music of the types the f ish had alreadylearned to classify S+ was the familiar blues song described aboveand S was the unfamiliar Fugue 2 from Book I of Bachrsquos Well-Tempered Clavier To minimize the presence of extraneous cues allthe performances were done by the same musician with the sameequipment (a Kurzweil Model k2000vp keyboard Young Chang Re-search and Development Institute Waltham MA) the same se-quencing software (Studio Vision Pro Version 40 Opcode SystemsNashville TN) and the same settings for volume and for timbre(acoustic piano) Because the new stimuli were so short that theywould repeat after only a few trials rote memory could play a rolein their discrimination and thus the operative level of stimulus con-trol was being allowed to potentially regress from categorization todiscrimination

The initial synthetic stimuli turned out to trigger a deteriorationin classification accuracy (Figure 11 Session 13) It seemed possi-ble that this was an artifact of the musical translation process be-cause even humans had some difficulty recognizing the John LeeHooker song in synthetic form It had gone from bluesy to bouncyits original bass inflections were absent and there was no melodicvoice comparable with that of the singer Therefore at Session 24 Iintroduced a second generation of stimuli S+ remained the samepiece but the performance was somewhat more faithful to themodel The old S (the Bach fugue) had been much shorter than S+and thus had been repeating more often so it was replaced by a syn-

thesized rendition of the f irst movement of Vivaldirsquos ConcertoGrosso in A minor Opus 3 No 6 whose duration more closelymatched that of S+ In addition the timbre of the blues was changedfrom acoustic piano to rock piano thus adding timbre as an availablediscriminant However from Session 47 until the end of the experi-ment S+ and S again had timbre in common specifically rockpiano (starting in Session 47) chiffloot (starting in Session 55) andguitar (starting in Session 62)

ResultsWith the first presentations in a synthetic timbre discrim-

ination accuracy deteriorated (Figure 11 Sessions 13ndash23)perhaps because the first synthetic S+ was not a good enoughexemplar of the blues genre Pepi essentially ceased re-sponding during this time and had to be dropped from thestudy Starting at Session 24 with improved stimuli and adifference in timbre between S+ and S the behavior ofboth remaining subjects immediately changed and there-after their discriminative accuracy improved continually

When S+ and S were again made identical in timbre(Session 47) accurate classification persisted despite aperformance decrement probably related to the loss of asalient cue When the same pair of MIDI sequences waspresented in additional timbres generalization of accurateclassification to the new sounds appeared seamless The datafrom Session 47 and onward demonstrate [Sessions 18ts(17) gt 16 ps lt 001] that koi are capable of discriminat-ing polyphonic music on the basis of features other thanthe timbre of individual tone sources

EXPERIMENT 4 Discrimination of Melodies

Without Timbre Cues

After observing that instrumental timbre seemed not tobe a necessary discriminant in polyphonic music I inves-tigated whether timbre was necessary for koi to discrimi-nate single-voice musicmdashthat is melodies

MethodIn order to familiarize the subjects with the S+ melody and also

in hopes of rehabilitating Pepi this experiment began with severalsessions of collective exposure to a sound-versus-silence contin-gency CRF signaled by the music that would later be the S+ in thesound-versus-sound discrimination alternated with extinction sig-naled by silence In this group pretraining Pepi was observed bothpressing the button and taking pellets from the nipple but when sub-sequently isolated for melody discrimination sessions he consis-tently shied away from the nipple and again had to be dropped as asubject

The stimuli for the melody discrimination experiment (Figure 12)were all derived from the theme from Paganinirsquos 24th Caprice forsolo violin which is perhaps best known from Rachmaninoff rsquosldquoRhapsody on a Theme by Paganinirdquo S+ was the original melody asperformed on the MIDI keyboard S was derived from S+ by usingthe transformation described by Poli and Previde (1991) By using acomputer to modify the MIDI score S+rsquos order of pitches was re-versed whereas its original order of note durations was retained Inother words the first note of S got the duration of S+rsquos first notebut the pitch of S+rsquos last note the second note of S got the durationof S+rsquos second note but the pitch of S+rsquos next-to-last note and so onThis procedure can be thought of as retaining the rhythm track while

0

1

2

3S

lop

e (

ch

ang

ese

ssio

n)

1 2 3 4

Reversal Number

OroBeauty

Pepi

Figure 10 Experiment 2 (iterated reversals) improvementtrends For Beauty and Oro the improvement rate (Figure 9 re-gression line slopes percentage of nonresponse S trials per ses-sion) increases with each reversal

MUSIC DISCRIMINATIONS BY CARP 349

reversing the pitch track The result is two stimuli that are ldquoidenticalwith respect to their mean frequency note duration and rhythm butnoticeably different in their melodic patternsrdquo (Poli amp Previde 1991p 12) Such a pitch-track-reversed melody differs from a completelybackwards melody only in rhythm sacrificing the linkage betweeneach pitch and its original duration in order to preserve the originalsequence of durations per se (If the original melodymdashunlike the

Rachmaninoffmdashhas a palindromic rhythm track the pitch-track -reversed melody and the completely backwards melody are identical)The melodies were recorded using the same MIDI apparatus as thatdescribed above To enhance clarity the tempo was somewhat slowerthan that of the usual piano performance

Over the course of 53 sessions the instrumental timbre alternatedsix times between strings and acoustic piano but in any given ses-

0

25

50

75

100

Tri

als

wit

h N

o P

res

s

S+

ITI

S-

Beauty

0

25

50

75

100

Tri

als

wit

h N

o P

ress

S+

ITI

S-

Oro

Same Timbre Different Timbre Same Timbre

S+S-ITI

Pepi ceased responding

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 Session Number

S+

ITI

S-

Pepi

Figure 11 Experiment 3 (transition to MIDI and timbre study) percentages of S+ and S trials dur-ing which the fish did not press the button During the first 12 sessions the stimuli consisted of a singletrack from each of the two commercial recordings the subjects had last heard 10 months earlier at theconclusion of the iterated-reversal experiment the immediate resumption of accurate discrimination sug-gests long-term memory of training The circled data points (Sessions 13 and 24) indicate the introduc-tion of the first- and second-generation synthetic music From Session 47 until the end of the experimentS+ and S had identical timbre each boxed data point pair indicates the first presentation of a new tim-bre Session 47 rock piano Session 55 chiffloot and Session 62 guitar Crosses denote silence

350 CHASE

sion S+ and S always had the same timbre The discrimination pro-tocol was unchanged from the previous experiments except that thesession termination trigger was raised from 50 to 55 pellets As a pre-liminary test for a possible perceptual invariance (Hulse Takeuchi ampBraaten 1992) S+ was transposed down a fifth in Sessions 51ndash52

After 53 sessions it was discovered that the MIDI technology hadintroduced artifactual differences between S+ and S A musicallyattuned visitor to the lab detected minor variations in note durationsbetween the two stimuli which apparently had resulted from incor-rect handling of the attackndashsustainndashdecay envelopes of S+rsquos recordednotes There also turned out to be subtle volume differences whichwere said to have resulted from the combination of the MIDI scoreediting process and the volume compression function in the digitalaudio tape (DAT) recorder used to create stimulus master tapesThese differences were confirmed by careful examination of thewaveforms using a computer oscilloscope Therefore a second gen-eration of S was created by direct numerical substitution of the S+pitches into the MIDI score in reverse order and by recording a newmaster tape with all volume compression disabled The correctionswere verified by waveform analysis

After eight sessions with the second-generat ion S both S+ andS were shortened by the removal of each onersquos distinctive initial noteand seven sessions later they were further shortened by the removal oftheir remaining initial six and final four notes The purpose of thesestimulus contractions was to look for behavioral disruption that might

indicate that the subject had been discriminating the melodies on thebasis of such local features as the absolute pitch of the initial note

Results and DiscussionBeautyrsquos performance inexplicably deteriorated to the

point where he had to be dropped as a subjectFigures 13 and 14 report the performance of Oro the only

fish to complete the melody experiment The data showthat without timbre cues Oro clearly discriminated betweenthe two melodies [in each stimulus condition (ie second-generation S first-note-removed and both-ends-clipped)5 final sessions t(4) gt 10 p lt 001]

Oro responded more to S+ than to S even in the veryfirst session with melodic stimuli Familiarization with theS+ during pretraining could well have contributed to thisresponse bias perhaps partly because music heard in asound-versus-silence context had consistently become theS+ in a subsequent sound-versus-sound discriminationHowever the MIDI artifacts in the first-generation stim-uli might also have played a role

Session 54 in which the corrected S was introducedmarks a significant reduction of the separation between

Figure 12 Experiment 4 (melody discrimination) musical scores of the normal (S+) and pitch-reversed (S )melodies

MUSIC DISCRIMINATIONS BY CARP 351

the S+ and the S nonresponse percentages [two-tailed two-sample t test assuming unequal variances contrasting themean difference between S and S+ nonresponse per-centages before and after the change 8 observations just be-fore the stimulus change vs 8 observations just after t(11) =277 p lt 019] This implies that the rather subtle artifactsin the original S had indeed been exploited as discrimi-nants

One oddity is the fact that although the stimuli changedsignificantly in Sessions 54 (second-generation S ) and62 (removal of the first note of S+ and S ) in each case

a pronounced anomaly in Ororsquos performance occurred inthe following session

Studies of melody discrimination in animals have oftenfound that the behavior was controlled by local featuressuch as timbre pitch register or the absolute pitch of the ini-tial note rather than by the melodic patterning per se(DrsquoAmato amp Salmon 1984 Hulse amp Cynx 1985 Hulseamp Page 1988 Poli amp Previde 1991) (In this paper for theterm local properties I follow the convention of referringnot only to features like distinctive individual notes whichare clearly local in a temporal sense but also to features

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 70

Session Number

S+

S-

= Piano= Down a fifth= wo 1st note= wo 1st 7 amp last 4 notes

S+S-ITI

Figure 13 Experiment 4 (melody discrimination) trials with no responses The MIDI timbre was violin except for 13 sessions ofpiano as marked The corrected S was introduced at Session 54 The first notes of S+ and S were removed at Session 62 The sixinitial and four final notes were removed at Session 69 Crosses denote silence

Figure 14 Experiment 4 (melody discrimination) all responses Sessions terminated with the S+ trial in which the 55th pel-let was dispensed Crosses denote silence

0

20

40

60

All

Pre

sses

0 10 20 30 40 50 60 70

Session Number

S+

S-

Oro

S+S-ITI

352 CHASE

like timbre and pitch register which although recogniz-able in any local segment can be constant over the dura-tion of the stimulus and which therefore might arguablybe called global properties) It should not be surprisingthat with sequential stimuli such as sound animals oftenexploit local features in preference to global pattern fea-tures In the acoustic domain features that are instantly rec-ognizable presumably confer a survival advantage not onlyon listeners but also on creatures in whose interest it is tobe identifiable by sounds they make Oro did not have tim-bre available as a discriminant but there is no conclusiveevidence that he did or did not use other local features andit is not known which if any global features he might haveused

It warrants mention that in this type of discriminationexperiment inaccurate responding need not imply that thesubject is musically insensitive because musical sensitiv-ity can actually confound discriminative accuracy if bothstimuli are musically plausible or stylistically similar In-deed throughout this experiment the stimuli were moni-tored through a speaker in the laboratory office and S+ andS became so familiar and the pitch-track-reversed Ssounded so pleasing that human observers occasionallybecame confused as to which reinforcement contingencywas in force in the tank

The finding that Oro did not need timbre cues to dis-criminate melodies contrasts sharply with the result in ratsreported by Poli and Previde (1991) Using as stimuli for-ward and pitch-track-reversed versions of the melodyldquoFregravere Jacquesrdquo they tested for discrimination on the basisof melodic pattern The rats had neither previous experi-mental experience nor prior familiarity with music In anattempt to preclude the exploitation of local features suchas the absolute pitch of distinctively positioned notes each15-sec stimulus presentation began at a randomly chosenposition within the melody Different groups of subjectswere asked to discriminate two melodic stimuli that dif-fered in melody only in timbre only or in both attributesHowever the stimuli were never heard as unitary melodiesfrom start to finish and were presented in a continuousstream of randomly sequenced exposures with responsesin the presence of S+ being reinforced only on an FR-5schedule This would seem to be such a formidable task asto make it unsurprising that animals failed except when tim-bre a consistent property of every note in each stimuluswas available as a discriminant However Poli and Previdedid suggest that rats might well prove able to discriminatemelodies without timbre cues under other conditions

CONCLUDING REMARKS

The distinction between local features and pattern fea-tures although it arose in connection with melody dis-crimination is equally relevant to the categorization ex-periment To say that in classifying music as blues orclassical the koi might have been responding to deepgeneric attributes is not to say that they were necessarilyusing anything other than local cues because the diag-

nostic property could have been a particular combinationof timbre loudness pitch brief rhythmic or melodic fig-ures and other such local features A human scanning aradio dial requires only a fraction of a second to identifythe genre of a given station hardly enough time for patternfeatures to manifest themselves so a brief sample of musiccould well contain something recognizable to an animalthat had a rote store of auditory feature memories Localfeatures might control classification behavior even whenthere is extensive exposure to a stimulus Conceivably an-imals could acquire a functional understanding of musicentirely on the basis of the distribution and frequency ofvarious combinations of essentially local features with-out regard to the artistic pattern features in terms of whichmusical genres are commonly defined

Prior to this series of experiments the prevailing opinionappeared to be skepticism as to whether koi could dis-criminate one piece of music from another under any cir-cumstances Now it appears that these animals can discrim-inate polyphonic music discriminate melodic patternsand even classify music by artistic genre As far as I knowthese experiments presented the most complex auditorystimuli to which fish have ever been shown capable ofmaking sophisticated discriminative responses Howeverthere remains the task of elucidating the stimulus controlfunctions of the constituents of that complexity such aspattern features local features and simple properties of thestimulus as a whole The present work was intended as ex-ploratory rather than explanatory and the results clearly ex-tend the known envelope of auditory capabilities in fish

REFERENCES

Baron M R (1965) The stimulus stimulus control and generaliza-tion In D I Mostovsky (Ed) Stimulus generalization (pp 62-71)Stanford CA Stanford University Press

Chase A R amp Hill W (1999) Reliable operant apparatus for fishAudio stimulus generator response button and pellet-dispensing nip-ple Behavior Research Methods Instruments amp Computers 31 470-478

Coombs S Jannsen J amp Montgomery J C (1992) Functional andevolutionary implications of peripheral diversity in lateral line sys-tems In D B Webster R R Fay amp A N Popper (Eds) The evolu-tionary biology of hearing (pp 267-294) New York Springer-Verlag

DrsquoAmato M R amp Salmon D P (1982) Tune discrimination in mon-keys (Cebus apella) and rats Animal Learning amp Behavior 10 126-134

DrsquoAmato M R amp Salmon D P (1984) Processing of complex au-ditory stimuli (tunes) by rats and monkeys (Cebus apella) AnimalLearning amp Behavior 12 184-194

Fay R R (1988) Hearing in vertebrates A psychophysics data-bookWinnetka IL Hill-Fay Associates

Fay R R (1992) Analytic listening in goldfish Hearing Research 59101-107

Fay R R (1994) Perception of temporal acoustic patterns by the gold-fish (Carassius auratus) Hearing Research 76 158-172

Fay R R (1995) Perception of spectrally and temporally complexsounds by the goldfish (Carassius auratus) Hearing Research 89146-154

Fay R R (1998) Auditory stream segregation in goldfish (Carassiusauratus) Hearing Research 120 69-76

Fay R R amp Ream T J (1986) Acoustic response and tuning in sac-cular nerve fibers of the goldfish (Carassius auratus) Journal of theAcoustical Society of America 79 1883-1895

Hartman W M (1988) Pitch perception and the segregation and inte-

338 CHASE

been registered The unconditioned reinforcer was food in the formof 20 mg-sinking pellets (Noyes formula JG) The pellets weredropped by an automatic feeder (Gerbrands G5120 or MED [Geor-gia VT] Model ENV 203-20) into a plastic tube that terminated un-derwater in an infantrsquos Stage One nipple (Johnson amp Johnson Skill-man NJ) that had been modified to let fish suck the pellets out Theinstantaneous conditioned reinforcer was an external light that back-lit the nipple A computer controlled the experiment and sessionswere videotaped

Preliminary PhaseThe processes of magazine training and of familiarization with

the response button the stimulus presentation system and the restof the apparatus are described in detail in Chase and Hill (1999) Be-fore conducting the genre discrimination experiment it was neces-sary to test the novel apparatus and the intended discrimination pro-tocol For example one objective was to verify that the new horizonta lresponse button did not artificially inflate response rates either bybeing intrinsically reinforcing or by eliciting instinctive mouthingthat could be mistaken for a discriminative response

The subjects were given a simple discrimination taskmdashnamelysound versus silencemdashwhich is described in detail in Chase and Hill(1999) The procedure presented randomly timed intervals (typicallybetween 40 and 90 sec) of music (S+) and silence (S ) in alternationand reinforced each response that was made in the presence of musicwith food To ensure that the onset of music would never reinforcea response made in silence any response made within 20 sec beforethe scheduled end of a silent interval prolonged the silence by reset-ting the countdown timer to 20 sec The reinforcement schedule wasmultiple continuous reinforcement-extinction (CRF-extinction)mdashthat is while music was playing every response was reinforced witha food pellet and during silence no response was reinforced A ses-sion ended with the S+ trial in which the 50th reinforcement wasdispensed

Because CRF provides informational feedback on every responsea subject could ldquofakerdquo a sound discrimination at least in the senseof exhibiting an appropriate response rate differential merely by

sampling and discriminating the prevailing reinforcing contingencyHowever if a fish suppressed responding substantially more in thepresence of one kind of stimulus than in the presence of the other itwould be clear that the fish was not routinely sampling the buttonand thus that it was under the control of the sound As is shown inFigure 3 Beauty and Oro met this standard within the first few ses-sions The characteristically hyperactive Pepi went 13 sessions be-fore his first S trial during which he did not respond at all butotherwise from the start he was much like the other subjects in ex-hibiting downward trends in the average number of responses perS trial and in the percentage of his total responses that occurredduring S (Chase amp Hill 1999)

In Figure 3 and in all other graphs of results the session axis de-notes experimental workdays in each of which a single set of stim-uli was used with all subjects that ran that day Every workday is in-dicated on every subjectrsquos session axis but an individual subjectrsquosstatistics are based on his actual runs only Skipped sessions wererare and were caused by anomalous conditions that either preventedan animalrsquos participation outright or else threatened to render mean-ingless any data that might be taken The fact that the results wereanalyzed in terms of within-subjects comparisons renders immater-ial such fine-grained differences between the experiences of differ-ent subjects

The final function of the sound-versus-silence task was to accus-tom the subjects to responding in the presence of the music that theywould later hear as the first S+ in the genre discrimination task andtherefore all of the sound stimuli were taken from John Lee Hook-errsquos Blues Before Sunrise CD The hope was that this preparationwould facilitate the acquisition of the musicndashmusic discrimination

EXPERIMENT 1Discrimination and Categorization Based on

Musical Genre

In this experiment it was asked whether fish can learnto discriminate between two stylistically different musical

Figure 2 Working end of the experimental tank as seen by the video camera (not shown) includes a parti-tion (P at the silicone joints) a filter (F) a tank tray (T) a gravel bed (G) a speaker (S) a response button (B)a light (L the conditioned reinforcer) which shines through a light-diffusing mylar (M) onto a nipple (N) a pel-let dispenser (D) and an LED (O) which shows the camera that the computer has registered a response FromldquoReliable Operant Apparatus for Fish Audio Stimulus Generator Response Button and Pellet-Dispensing Nipplerdquo by A R Chase and W Hill 1999 Behavior Research Methods Instruments amp Computers 31 p 471Copyright 1999 by the Psychonomic Society Reprinted with permission

MUSIC DISCRIMINATIONS BY CARP 339

stimuli and if so whether they can generalize to unfamiliarmusic from the same stylistic categories capabilities pre-viously demonstrated in pigeons by Porter and Neuringer(1984)

A standard demonstration of categorization behaviorbegins by training an animal to classify the members oftwo nonoverlapping sets of stimuli by responding only inthe presence of the members of one particular set Each setis an experimenter-defined category and each stimulus isan exemplar of one category The animal is said to havelearned the two categories if it then responds appropriatelyto novel exemplars of each and if there is reason to believethat it can also discriminate exemplars within each set aswell as between sets The latter criterion ensures that theanimal was perceiving categories rather than exhibitingcategorical perception that is the animalrsquos treating cer-tain exemplars alike must not be due merely to an inabil-ity to tell them apart (Herrnstein 1992 Sturdy PhillmorePrice amp Weisman 1999)

In visual categorization studies pigeons have beentrained to classify photographs according to whether theydo or do not contain people water fish aerial views of aparticular location tree leaves damaged by a particularspecies of caterpillar and other such complex criteria (Herrn-stein 1992) If intermittent reinforcement is used partic-ular exemplars might be repeated yet never associatedwith reinforcement if there is improvement in the accu-racy of classification of even these stimuli it is reason-able to conclude that the animal is responding to them onthe basis of features that imply membership in a specificcategory instead of as isolated stimuli The training setscan range from closed and repetitive stimuli with testingdone by using novel stimuli as probes to streams of con-tinually novel stimuli in which case classification accu-racy measures categorization behavior on an ongoingbasismdasheven under CRFmdashbecause rote memory (at leastof whole stimuli as opposed to features) can play no role(Malott amp Siddall 1972)

Categories can also be defined with no systematic rela-tionship to stimulus properties so that the only way to dis-

tinguish them is through rote memory of the reinforce-ment contingency associated with each exemplar Rotememory capacity in animals can be considerable Vaughanand Greene (1984) trained pigeons to sort visual imagesinto rote categories and found that they could easily mem-orize hundreds of pictures and remember them for at least2 years In foraging and food-hiding birds such as theHawaiian honeycreeper and Clarkrsquos nutcracker estimatesof the memory capacity for locations range well into thethousands (Herrnstein 1992)

The protocol in the present study used closed trainingsets and CRF but within-session repetition was almostnonexistent The first presentation of a pair of novel CDsconstituted a stream of novel stimuli and served as a mea-surement probe

Because of the prevailing skepticism that koi could dem-onstrate the capabilities I was hoping to find I tried to makeevery task as easy as possible for the animals a constraintthat dictated some procedural choices that might be re-garded as unconventional One example is the use of a freeoperant and CRF rather than discrete trials or a lean rein-forcement schedule Another is the use of reversals in-stead of extinction trials in order to demonstrate control bystimuli rather than by prevailing reinforcement contin-gency The rationale for CRF was to minimize stress andmaximize feedback given that the exertional cost of but-tonpressing appeared relatively high and that consequentlythe maximum possible response rate was expected to berelatively low Unlike a discrete-trials procedure the free-operant approach fixed each trialrsquos stimulus presentationtime while letting the numbers of responses and reinforce-ments vary My intention was to minimize interferencewith the formation of associations between the positivestimulus and the instantaneous conditioned reinforce-ment or the actual consumption of food With respect toelucidating the stimulus control I was concerned that aswitch to total extinction might cause excessive emotionalside effects and reduce the subjectsrsquo long-term viabilityTherefore in my experiments the usual role of extinctiontrials was played by reversals In a study with so few sub-

0

50

100

0 10 20 30 40

Beauty

S+

S-

Tri

als

wit

h N

o P

ress

0 10 20 30 40

Oro

S+

S-

0 10 20 30 40 Session Number

Pepi

S+

S-

Session NumberSession Number

Figure 3 Preliminary phase (sound vs silence) percentages of S+ and S intervals in which the fish did not press the button at allA comparatively high percentage of nonresponding for S indicates successful discrimination Crosses denote silence

340 CHASE

jects reversals can also act like counterbalancing in con-trolling for possible differences in familiarity and saliencywith respect to the stimuli designated as S+ or S Re-versals have the further advantage of offering glimpses ofadditional phenomenamdashin particular reversal learningper se

MethodThe protocol was an extension of that used in the preliminary

sound-versus-silence discrimination as described above Howevernow there were three kinds of intervalsmdashnamely S+ trials (bluesmusic) S trials (classical music) and a silent intertrial interval(ITI) Also the intervals were now of fixed duration 30 sec for S+and S sound trials and 15 sec for the ITI During the ITI a cor-rection procedure was programmed so that any response that oc-curred less than 10 sec before the silence was scheduled to end pro-longed the ITI by resetting the countdown timer to 10 sec Thesequence of S+ and S trials was randomized in real time but a ses-sion always began with two successive S+ trials and there could beno more than three consecutive trials with any one stimulus type Asession ended at the end of the full S+ interval during which the 50threinforcement was delivered

An important aspect of the procedure was that the computer didnot restart the piece of music at the beginning of each trial but in-stead resumed the CD where it had left off (unless there were fewerthan 30 sec of music remaining on that track in which case the stim-ulus would be the first 30 sec of the following track the intent beingto try to ensure that every stimulus would be a full 30 sec of music)Each of the S+ and S CDs contained roughly 120 distinct excerpts and a session ended with the S+ excerpt during which the 50th re-sponse was made so it was rare for a session to run long enough forany CD to start over and thus there was relatively little within-session repetition of stimuli Each excerpt was effectively a separatemini-piece in one of the two styles represented by the two CDsThus even within a single piece of music or CD track what the fishconfronted was essentially a categorization problem in contrast to adiscrimination between two brief musical fragments that would berepeated identically many times in each session Because the com-puter consistently divided a CD into the same sequence of fixed-length excerpts each time a musical CD was somewhat analogousto a tray containing 120 photographic slides as a source of exem-plars in a visual categorization experiment

Figure 4 summarizes the sequence of experimental conditions andthe recordings used starting with the preliminary sound-versus -silence phase The computer software allowed individual tracks to bemarked for exclusion and as is noted in the CD reference list intwo of the blues CDs certain tracks were excluded because they con-tained speech or silence

In the beginning of Experiment 1 (Sessions 40ndash55) the stimulussources were two entire CDs S+ was John Lee Hookerrsquos Blues Be-fore Sunrise (carried over from the sound-versus-silence discrimina-tion) and S was Bach oboe concertos (familiar from a priorstudy) Over the course of the first 6 sessions 2 fish showed no ev-idence of learning the discrimination whereas the 3rd achieved asuccess that proved short-lived Therefore I simplified the task byrestricting the stimuli to a single track from each CD The first suchpair of tracks was used for 30 sessions and over the next 15 sessionsthree new pairs of tracks were used each pair for 5 consecutive ses-sions After the animals had learned to discriminate a single classi-cal track from a single blues track these four times I again allowedthe stimuli to come from the entire CD of each genre

Because CRF was always in effect during S+ providing feedbackas well as reinforcement the best way to reveal whether the fish wereclassifying the music on the basis of a categorical principle ratherthan on the basis of rote memory was to present novel stimuli There-fore scattered throughout the experiment were nine probe sessions in

which both the S+ and the S CDs were novel These were Sessions115 120 131 138 152 157 163 168 and 177 The music was se-lected for diversity within the genre S+ included four different per-formersrsquo CDs plus five compilation CDs with more than 20 addi-tional blues performers S consisted of six baroque-style CDs andthree non-baroque composersmdashspecifically Mozart Beethovenand Schubert

The buttonpressing response involves a fishrsquos entire body sincethe fish must position itself over the button and essentially ram itTherefore such a response is inherently somewhat slowmdashfar slowerthan for example a birdrsquos peck at a key or a ratrsquos press of a lever Be-cause the fish typically would not hover over the button and becausethey appeared to commit to a response by swimming in from a dis-tance after each S+ interval the silent ITI began with a grace periodof 1 sec during which a buttonpress would still be counted and re-inforced on the assumption that the response had begun during S+

During Sessions 147ndash149 the 200-Hz high-pass filter was turnedon in order to minimize stimulation of the lateral line The idea wasto try to ensure that the discrimination between blues and classicalwould be made on the basis of input from the fishrsquos inner ears thesensory system presumably most capable of detecting the f ine-grained acoustic features of music that form the basis for stylisticdistinctions by humans

The possibility of acoustic artifacts owing to hardware was testedby a control procedure in which the blues and the classical CDs wereeach loaded into the drive programmed for the other (Sessions 182ndash238) The effect was to reverse the definitions of S+ and S (ie toreinforce responses to classical music but not to blues) This was ex-pected to produce a dramatic decrement in accuracy which woulddemonstrate that responding had indeed been under the control ofthe musical content of the S+ and S channels

Results and DiscussionThe use of CRF imposed the obligation to verify that

the subjects were discriminating the stimuli and notmerely the current state of the multiple CRF-extinctionschedule Proof that a subject was not being cued by feed-back from routine test responses would be a statisticallysignificant difference between the percentages of S andS+ trials in which the subject did not press the button atall Such a finding would allow rejection of the hypothe-sis that the subject had been testing the button equally dur-ing both stimulus conditions The alternative hypothesis isdirectional in that beyond exhibiting a difference per sean auditorily discriminating subject would be expected toignore the response button more during S than during S+Therefore unless otherwise specified throughout thispaper significance is reported in terms of the p value of aone-tailed paired t test (Microsoft Excel 97 SR-1) on thenonresponse percentages associated with the two stimulustypes in each of n sessions the alpha level used was 05

As is indicated graphically in Figures 5 and 6 all 3 koidiscriminated blues from classical music and this behav-ior generalized into an ability to classify unfamiliar ex-emplars by genre [for each of the 3 subjects 9 probe ses-sions t(8) gt 10 p lt 001] To my knowledge this is thefirst demonstration in fish of open-ended categorization(Herrnstein 1992) and of any kind of categorization withauditory stimuli

Figure 5 shows the percentages of S+ and S trials inwhich there was no responding In Session 115 the firstprobe Beauty responded only during S+ and not at all dur-

MUSIC DISCRIMINATIONS BY CARP 341

ing S or ITI In Probe Session 138 the novel S was Vi-valdi guitar music which proved to raise problems Figure 6shows all the responses for each session note the higherS response rate at Session 138 Session 182 was the first

control-by-reversal session Sessions 138 and 182 are fur-ther discussed below

The data from the probe sessions are plotted in Figure 7and are shown in historical context in Figure 5 Figure 7

Figure 4 Experiments 1 and 2 (categorization and iterated reversals) stimulus chart Each column representsa single stimulus CD which is identified by text that starts in that column at the bottom of the figure Each rowrepresents a group of sessions Bullets indicate the CDs presented in their entirety as the S+ and S in each ses-sion group whereas the numbers associated with Sessions 56ndash100 identify the specific CD tracks used as stim-uli A triple bullet marks the first presentation of a given CD a single bullet denotes a stimulus heard previ-ously Rows in which both stimuli are represented by triple bullets denote groups of sessions in which the firstone exposed the subject to all-novel stimuli and thus served as a probe session

342 CHASE

also shows means for the nonprobe and the probe sessionsin the session range 115ndash181 The fish classified musicwith which they had had no training about as accurately asthey classified familiar training stimuli This generaliza-tion to unfamiliar exemplars demonstrates that the fishwere not relying on rote memory but were instead exhibit-ing open-ended categorization (Herrnstein 1992)

To assess whether the fish were exhibiting true percep-tion of categories preclusion of categorical perception(ie the inability to discriminate exemplars within a cat-egory) was necessary The great complexity of musicalstimuli renders likely the existence of a mix of feature di-mensions on the basis of which a sample only a few sec-onds long suffices to distinguish any two pieces or evendifferent performances of the same piece The blues stim-uli ranged from John Lee Hooker to Sonny Boy William-son and the classical ranged from baroque to Schubertboth categories featured a variety of ensembles It is im-plausible that recordings that sound so very different tohumans would be completely indistinguishable to thesefish The result of Experiment 4 below provides strongadditional evidence Koi can discriminate generically simi-lar melodies which implies that they can discriminategenerically similar recordings that differ along a multi-plicity of dimensions of which melody is only one

In Figures 5 and 6 the data for Sessions 182ndash192 showthe disruption of performance following the reversal of thereinforcement contingencies This reversal served as acontrol procedure the result of which confirmed that re-sponding was indeed under the control of the musical con-tent as opposed to any electronic artifact in the S+ andS audio channels

In Sessions 138ndash144 the fish had unexpected difficultydiscriminating Vivaldi guitar concertos from a blues com-pilation Although it is plausible that the fish could havelearned that guitar sounds were characteristic of blues theguitar concertos arguably did not sound to humans as muchlike blues as like the Vivaldi cello concerto which was theprevious S and which the fish had had no trouble dis-tinguishing from blues Another possible source of confu-sion for the f ish was the fact that this S+ was the firstcompilation CD to be presented as a stimulus Thus the di-versity of blues styles distinguished this S+ CD from anyprevious one Given the fishesrsquo problem with this dis-crimination I paired the Vivaldi guitar concertos with somevery familiar John Lee Hooker (Sessions 145ndash146) Whendiscrimination did not improve I left these stimuli in placebut turned on the 200-Hz high-pass filter for three ses-sions (147ndash149) As can be seen from Figure 5 the resultof turning on the filter was an immediate improvement inperformance which persisted after the filter was turnedoff Apparently these particular stimuli were salient andhad similar features in the lower frequencies which con-fused the fish until the high-pass filter forced them to at-tend to higher frequency features on the basis of whichthe music was more readily discriminable It would alsoappear that the lateral line was not necessary for the dis-crimination of familiar music As DrsquoAmato and Salmon

(1982) noted ldquoIndividuals do not always rely on the sameproperty of the stimulus and may according to circum-stances shift their reliance from one feature to anotherrdquo(p 130) (In any case Vivaldi evidently can impress listen-ers in odd ways Porter amp Neuringer 1984 reported thata Vivaldi violin concerto sounded more like Stravinsky thanlike Bach to their pigeons as it did also to some humans)

Even a convincing demonstration of categorization canfail to identify the stimulus features that exert control atany given time especially if the stimuli are complex In par-ticular there can be uncertainty as to whether classificationbehavior had been under the stimulus control of the fea-tures in terms of which the experimenter had defined thecategories or whether the subjects had discovered an ef-fective discriminant of which the experimenter was unawareThe diversity of S+S pairings (see Figure 4) presum-ably rules out the possibility that the fish could have beenrelying on only a single discriminant such as timbre buta constant concern is the possible existence of a simple at-tribute that would have allowed the subjects merely to dis-criminate instead of categorizing In the present experi-ment the choices of stimuli and control procedures wereintended to ensure that all the available discriminants weresufficiently complex For example even if a fish used asthe discriminant the sound of a human voice which waspresent in virtually all of the blues but in none of the clas-sical the diversity of singing voices would imply open-ended categorization nonetheless

The possibility that the fish memorized individual or re-curring features cannot be ruled out An animal probablydoes exploit a collection of memorized features alongwith various abstracted properties It would be surprisingif no features at all were salient enough to be rememberedand one wonders whether it is even possible to abstract acategorical discriminant without having particular fea-tures in memory at least temporarily

The notion that koi might classify blues and classicalmusic on the basis of deeper generic attributes is supportedby the results of experiments reported below which indi-cate that timbre cues are not required Porter and Neuringer(1984) trained pigeons to discriminate baroque from mod-ern music using initial exemplars that could have been al-ternatively classified as organ and orchestral music but theeffective discriminant turned out to be something otherthan instrumental timbre In a recent report (Watanabe ampSato 1999) Java sparrows learned to discriminate pianomusic by Schoumlnberg from piano music by Bach and theythen correctly classified orchestral music as Schoumlnberg-like or Bach-like whether written by those two composersor by Carter and (even) Vivaldi Studies that analyze the per-ceptual world of pigeons in terms of multidimensionalscaling spaces reveal that the birds learn enough aboutnonexemplars to form a distinct category for them as wellas for exemplars In other words pigeons appear to eval-uate a stimulus not only as possibly a good exemplar but alsoas a good nonexemplar which is more work than binaryclassification logically requires (Herrnstein 1994) Giventhat the more features of the environment to which one is

MUSIC DISCRIMINATIONS BY CARP 343

sensitive the more information is available from which todiscern patterns and changes indications that animalslearn more than the minimal solution to classificationproblems involving complex stimuli suggest that as com-pared with trying to ignore as much as possible of theworld evolution favors embracing its complexity

EXPERIMENT 2 Iterated Reversals

MethodThe first categorization session in which the contingencies were

reversed had served as a control procedure This experimental con-

0

25

50

75

100

Tri

als

wit

h N

o P

ress

Beauty

S-

S+

0

25

50

75

100

Tri

als

wit

h N

o P

ress

Oro

S-

S+

200 Hz filter

0

25

50

75

100

Tri

als

wit

h N

o P

ress

40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

Session Number

Pepi

S+

S-

S+ S- ITI

Figure 5 Experiment 1 (categorization) percentages of S+ (blues) and S (classical) trials and intertrial intervals (ITIs silence)during which the fish did not press the button at all plotted for each session The greater the separation between a sessionrsquos S+ andS nonresponse percentages the more clearly the subject was discriminating the stimuli as opposed to responding indiscriminatelyand receiving feedback from the reinforcement contingency The boxed data points indicate probe sessions The bar from Sessions147ndash149 shows where the 200-Hz low-frequency cutoff filter was used The circled data points (Session 182) indicate the first control-by-reversal session In the reversal sessions (182ndash192) S+ (still represented by open squares) was now classical music whereas S (stillrepresented by filled triangles) was blues Crosses denote silence

344 CHASE

dition (ie with blues now the S and classical now the S+) wasthen extended into an iterated-reversal experiment The primary goalwas to test koi in reversal learning with complex auditory stimuliafter having found nothing in the literature on the subject of auditoryreversal learning in fish

A secondary goal was to prepare for a planned experiment with aclassification procedure involving two visually distinct buttons withresponses on a particular button to be reinforced only in the presenceof a particular type of music The rim of the original button had beenmachined from black Delrin A new rim was made from an ivory-

colored blank of the same plastic and installed after six sessions ofthe unsignaled reversal (ie no change in the button) Thereafterrim color alternated in synchrony with contingency reversals withblack and ivory signaling that S+ was blues and classical respec-tively The fish would experience a total of four color changes thefirst of which did not signal a contingency change

The sessions were terminated by either the trial in which the 50thpellet was dispensed or an elapsed time of 90 min whichever camefirst Altogether there were 119 sessions spanning four reversals(see Figure 4)

Figure 6 Experiment 1 (categorization) all responses Number of responses in each session during blues trials classical trials andintertrial intervals (ITIs) Under the reversal condition that began with Session 182 blues became S and classical became S+ Bluesresponse counts above 50 reflect the onset of extinction Reversal sessions in which the classical response count was less than 50 wereterminated at 90 min Crosses denote silence

0

20

40

60

80

100

120

All

Pre

sses

40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

Session Number

Pepi

0

20

40

60

80

100

120

All

Pre

sses

ITI

Oro

0

20

40

60

80

100

120

All

Pre

sses

BeautyBluesClassicalITI

MUSIC DISCRIMINATIONS BY CARP 345

Just before the first reversal the stimuli had been a House of Bluescompilation (S+) and a baroque horn compilation (S ) When thecontingencies were reversed making blues S and classical S+both stimuli were also replaced The first reversal stimuli were Bachoboe concertos (S+) and John Lee Hookerrsquos Real Folks Blues (S )both very familiar to the fish In the next three phases of the first re-versal three additional pairs of familiar CDs were used In the fifthand final phase of the first reversal the fish were exposed to entirelynovel stimuli (S The Blues Story compilation S+ Bach triosonatas) As in the categorization study the first session with novelstimuli (Session 224) served as a probe testing for open-ended cat-egorization Blues and classical successively exchanged roles as S+and S in three additional reversal phases all using familiar stim-uli As can be seen in Figure 4 when the first and third reversals oc-curred at least one stimulus CD changed as well The final reversalbrought the contingencies back to where they had been before thefirst reversalmdashnamely with blues as S+ and classical as S

ResultsThe first reversal (Session 182) produced considerable

behavioral disruption and erroneous responding (see Fig-

ures 8 and 9) In the first 6ndash9 sessions the increase in re-sponding to the genre newly become S+ was insufficientfor any fish to earn 50 reinforcements within the 90-mintime limit (Figure 8) Beauty and Oro steadily improvedand were reliably discriminating by the 16th and 23rd ses-sions respectively Pepi achieved significance by Session 9but then his performance was substandard until Session 27[5 sessions ts(4) gt 229 p lt 010 p lt 009 and p lt 042respectively] Near the end of the first reversal the probesession (224) revealed that the classification behavior ex-hibited by Beauty and Oro was clearly open-ended catego-rization With each successive reversal it took fewer sessionsfor Beauty and Oro to demonstrate clear discrimination(Figures 9 and 10) Even Pepi eventually learned each re-versalmdashalbeit while continuing to call attention to the ex-istence of considerable and systematic individual differ-ences among fish In Figure 9 least-squares regressionlines are plotted for S nonresponse data and as is shownin Figure 10 their slopes indicate improvement rates of

0

50

100 Beauty

0

50

100 Oro

0

50

100

Mean 115 120 131 138 152 157 163 168 177 Mean

Probe Sessions (Novel CDs) Probes

Pepi

Non probes

S+S-ITI

Tri

als

wit

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o P

ress

Tri

als

wit

h N

o P

ress

Tri

als

wit

h N

o P

res

s

Figure 7 Experiment 1 (categorization) categorization performance during probe ses-sions (ie all-novel stimuli) percentages of S+ trials intertrial intervals (ITI) and S tri-als in which the fish did not respond Black bars indicate S+ gray bars indicate S andwhite bars indicate ITI Low nonresponse percentages for S+ indicate a high likelihoodof responding during S+ whereas high nonresponse percentages for S indicate that thefish tended to ignore the button during S The leftmost ldquoMeanrdquo bars show the averagesof all the nonprobe sessions in the session range 115ndash181 and the rightmost ldquoMeanrdquo barsshow the averages of the probe sessions

346 CHASE

08 and 11 per session for Beauty and Oro respec-tively during the first reversal (Sessions 182ndash238) Overthe final 5 sessions of each reversal phase discriminationby Beauty Oro and Pepi was statistically significant at

levels always better than p lt 010 p lt 016 and p lt 042respectively [ts(4) gt 229] It can be seen in Figure 8 thatwith each reversal the increase in responding to the new S+was generally faster than the extinction to the former S+

0

20

40

60

80

100

120

All

Pre

sses

Beauty

0

20

40

60

80

100

120

All

Pre

sses

Oro

ITI

Session Number

blues

classical classicalbluesblues

0

20

40

60

80

100

120

All

Pre

sses

150 175 200 225 250 275 300

Pepi

classical

BluesClassical

Figure 8 Experiment 2 (iterated reversals) counts of all responses by session Note that in graphs of reversal data the symbols con-sistently indicate genre (open squares blues filled triangles classical) not stimulus semantics (S+ or S ) which of course change ateach reversal This convention highlights the fluctuating response pattern associated with each genre longitudinally as successive re-versals of reinforcement contingency produce disruption and then learning with increasing efficiency The primary session termina-tion trigger was the trial on which the 50th pellet was delivered but in the early sessions of the first reversal no subject made as manyas 50 ldquocorrectrdquo responses to the former S within the session time limit even while responding many more than 50 times without re-inforcement to the former S+ Note that the extinction-induced response frenzy associated with a genrersquos suddenly becoming S de-creases with each reversal Crosses denote silence

MUSIC DISCRIMINATIONS BY CARP 347

EXPERIMENT 3Transition to Synthetic Keyboard Music and

Polyphonic Discrimination with Identical Timbre

The next step was to try to extend the learned classifi-cation of natural music to MIDI (Musical Instrument Dig-

ital Interface) synthesized music in which S+ and Swere not distinguishable by timbre

MethodPretraining After the iterated-reversal experiment the fish re-

mained in the homeexperimental tank from which all the appara-tus had been removed and they were not exposed to music or to anytraining or experimental procedures for a period of 10 months The

Tri

als

wit

h N

o P

ress

0

25

50

75

100

Reversals

Oro

classical

blues

classical

classical

blues

bluesTri

als

wit

h N

o P

ress

0

25

50

75

100

150 200 250 300

Session Number

Pepi

0

25

50

75

100

First Reversal

Beauty

Probe

Tri

als

wit

h N

o P

ress

ITI

BluesClassicalITI

Figure 9 Experiment 2 (iterated reversals) percentages of trials with no responses by session Note the increasingly efficient learn-ing of nonresponding to each former S+ as shown by the increasing slopes of the least-squares regression lines Session 224 (dashedline) was a probe the accurate discrimination of entirely novel stimuli indicates that the fish were performing open-ended catego-rization Crosses denote silence

348 CHASE

work resumed with a reintroduction to the apparatus and protocol asleft off at the end of the fourth and final reversalmdashthat is with S+and S being blues and classical respectively However the fishwere also being prepared to encounter the synthetic stimuli that werebeing created at that time which consisted of a single short piecefrom each genre rather than a collection comparable in duration andvariety with the commercial CDs used previously Therefore in pre-training the stimuli were the same two CDs the subjects had lastheard (see Figure 4 Session 300) but only a single track from eachS was an excerpt from a Bach oboe concerto S+ was the John LeeHooker song ldquoOne Bourbon One Scotch and One Beerrdquo of whicha synthesized version was in the works

Initially Beauty and Oro seemed to manifest effects of the longhiatus in the form of low response rates (not enough to earn 50 pel-lets in a session) and some transient difficulties operating the buttonand taking pellets from the nipple However even allowing for somerelearning and the reduced size of the new stimuli the immediacywith which all 3 subjects exhibited highly accurate discriminationsuggests that the original discrimination training had been retained(compare the leftmost sessions in Figure 11 with the rightmost inFigure 9)

Procedure The new stimuli were musically simplif ied MIDIkeyboard renditions of music of the types the f ish had alreadylearned to classify S+ was the familiar blues song described aboveand S was the unfamiliar Fugue 2 from Book I of Bachrsquos Well-Tempered Clavier To minimize the presence of extraneous cues allthe performances were done by the same musician with the sameequipment (a Kurzweil Model k2000vp keyboard Young Chang Re-search and Development Institute Waltham MA) the same se-quencing software (Studio Vision Pro Version 40 Opcode SystemsNashville TN) and the same settings for volume and for timbre(acoustic piano) Because the new stimuli were so short that theywould repeat after only a few trials rote memory could play a rolein their discrimination and thus the operative level of stimulus con-trol was being allowed to potentially regress from categorization todiscrimination

The initial synthetic stimuli turned out to trigger a deteriorationin classification accuracy (Figure 11 Session 13) It seemed possi-ble that this was an artifact of the musical translation process be-cause even humans had some difficulty recognizing the John LeeHooker song in synthetic form It had gone from bluesy to bouncyits original bass inflections were absent and there was no melodicvoice comparable with that of the singer Therefore at Session 24 Iintroduced a second generation of stimuli S+ remained the samepiece but the performance was somewhat more faithful to themodel The old S (the Bach fugue) had been much shorter than S+and thus had been repeating more often so it was replaced by a syn-

thesized rendition of the f irst movement of Vivaldirsquos ConcertoGrosso in A minor Opus 3 No 6 whose duration more closelymatched that of S+ In addition the timbre of the blues was changedfrom acoustic piano to rock piano thus adding timbre as an availablediscriminant However from Session 47 until the end of the experi-ment S+ and S again had timbre in common specifically rockpiano (starting in Session 47) chiffloot (starting in Session 55) andguitar (starting in Session 62)

ResultsWith the first presentations in a synthetic timbre discrim-

ination accuracy deteriorated (Figure 11 Sessions 13ndash23)perhaps because the first synthetic S+ was not a good enoughexemplar of the blues genre Pepi essentially ceased re-sponding during this time and had to be dropped from thestudy Starting at Session 24 with improved stimuli and adifference in timbre between S+ and S the behavior ofboth remaining subjects immediately changed and there-after their discriminative accuracy improved continually

When S+ and S were again made identical in timbre(Session 47) accurate classification persisted despite aperformance decrement probably related to the loss of asalient cue When the same pair of MIDI sequences waspresented in additional timbres generalization of accurateclassification to the new sounds appeared seamless The datafrom Session 47 and onward demonstrate [Sessions 18ts(17) gt 16 ps lt 001] that koi are capable of discriminat-ing polyphonic music on the basis of features other thanthe timbre of individual tone sources

EXPERIMENT 4 Discrimination of Melodies

Without Timbre Cues

After observing that instrumental timbre seemed not tobe a necessary discriminant in polyphonic music I inves-tigated whether timbre was necessary for koi to discrimi-nate single-voice musicmdashthat is melodies

MethodIn order to familiarize the subjects with the S+ melody and also

in hopes of rehabilitating Pepi this experiment began with severalsessions of collective exposure to a sound-versus-silence contin-gency CRF signaled by the music that would later be the S+ in thesound-versus-sound discrimination alternated with extinction sig-naled by silence In this group pretraining Pepi was observed bothpressing the button and taking pellets from the nipple but when sub-sequently isolated for melody discrimination sessions he consis-tently shied away from the nipple and again had to be dropped as asubject

The stimuli for the melody discrimination experiment (Figure 12)were all derived from the theme from Paganinirsquos 24th Caprice forsolo violin which is perhaps best known from Rachmaninoff rsquosldquoRhapsody on a Theme by Paganinirdquo S+ was the original melody asperformed on the MIDI keyboard S was derived from S+ by usingthe transformation described by Poli and Previde (1991) By using acomputer to modify the MIDI score S+rsquos order of pitches was re-versed whereas its original order of note durations was retained Inother words the first note of S got the duration of S+rsquos first notebut the pitch of S+rsquos last note the second note of S got the durationof S+rsquos second note but the pitch of S+rsquos next-to-last note and so onThis procedure can be thought of as retaining the rhythm track while

0

1

2

3S

lop

e (

ch

ang

ese

ssio

n)

1 2 3 4

Reversal Number

OroBeauty

Pepi

Figure 10 Experiment 2 (iterated reversals) improvementtrends For Beauty and Oro the improvement rate (Figure 9 re-gression line slopes percentage of nonresponse S trials per ses-sion) increases with each reversal

MUSIC DISCRIMINATIONS BY CARP 349

reversing the pitch track The result is two stimuli that are ldquoidenticalwith respect to their mean frequency note duration and rhythm butnoticeably different in their melodic patternsrdquo (Poli amp Previde 1991p 12) Such a pitch-track-reversed melody differs from a completelybackwards melody only in rhythm sacrificing the linkage betweeneach pitch and its original duration in order to preserve the originalsequence of durations per se (If the original melodymdashunlike the

Rachmaninoffmdashhas a palindromic rhythm track the pitch-track -reversed melody and the completely backwards melody are identical)The melodies were recorded using the same MIDI apparatus as thatdescribed above To enhance clarity the tempo was somewhat slowerthan that of the usual piano performance

Over the course of 53 sessions the instrumental timbre alternatedsix times between strings and acoustic piano but in any given ses-

0

25

50

75

100

Tri

als

wit

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res

s

S+

ITI

S-

Beauty

0

25

50

75

100

Tri

als

wit

h N

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ress

S+

ITI

S-

Oro

Same Timbre Different Timbre Same Timbre

S+S-ITI

Pepi ceased responding

0

25

50

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100

Tri

als

wit

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o P

ress

0 10 20 30 40 50 60 Session Number

S+

ITI

S-

Pepi

Figure 11 Experiment 3 (transition to MIDI and timbre study) percentages of S+ and S trials dur-ing which the fish did not press the button During the first 12 sessions the stimuli consisted of a singletrack from each of the two commercial recordings the subjects had last heard 10 months earlier at theconclusion of the iterated-reversal experiment the immediate resumption of accurate discrimination sug-gests long-term memory of training The circled data points (Sessions 13 and 24) indicate the introduc-tion of the first- and second-generation synthetic music From Session 47 until the end of the experimentS+ and S had identical timbre each boxed data point pair indicates the first presentation of a new tim-bre Session 47 rock piano Session 55 chiffloot and Session 62 guitar Crosses denote silence

350 CHASE

sion S+ and S always had the same timbre The discrimination pro-tocol was unchanged from the previous experiments except that thesession termination trigger was raised from 50 to 55 pellets As a pre-liminary test for a possible perceptual invariance (Hulse Takeuchi ampBraaten 1992) S+ was transposed down a fifth in Sessions 51ndash52

After 53 sessions it was discovered that the MIDI technology hadintroduced artifactual differences between S+ and S A musicallyattuned visitor to the lab detected minor variations in note durationsbetween the two stimuli which apparently had resulted from incor-rect handling of the attackndashsustainndashdecay envelopes of S+rsquos recordednotes There also turned out to be subtle volume differences whichwere said to have resulted from the combination of the MIDI scoreediting process and the volume compression function in the digitalaudio tape (DAT) recorder used to create stimulus master tapesThese differences were confirmed by careful examination of thewaveforms using a computer oscilloscope Therefore a second gen-eration of S was created by direct numerical substitution of the S+pitches into the MIDI score in reverse order and by recording a newmaster tape with all volume compression disabled The correctionswere verified by waveform analysis

After eight sessions with the second-generat ion S both S+ andS were shortened by the removal of each onersquos distinctive initial noteand seven sessions later they were further shortened by the removal oftheir remaining initial six and final four notes The purpose of thesestimulus contractions was to look for behavioral disruption that might

indicate that the subject had been discriminating the melodies on thebasis of such local features as the absolute pitch of the initial note

Results and DiscussionBeautyrsquos performance inexplicably deteriorated to the

point where he had to be dropped as a subjectFigures 13 and 14 report the performance of Oro the only

fish to complete the melody experiment The data showthat without timbre cues Oro clearly discriminated betweenthe two melodies [in each stimulus condition (ie second-generation S first-note-removed and both-ends-clipped)5 final sessions t(4) gt 10 p lt 001]

Oro responded more to S+ than to S even in the veryfirst session with melodic stimuli Familiarization with theS+ during pretraining could well have contributed to thisresponse bias perhaps partly because music heard in asound-versus-silence context had consistently become theS+ in a subsequent sound-versus-sound discriminationHowever the MIDI artifacts in the first-generation stim-uli might also have played a role

Session 54 in which the corrected S was introducedmarks a significant reduction of the separation between

Figure 12 Experiment 4 (melody discrimination) musical scores of the normal (S+) and pitch-reversed (S )melodies

MUSIC DISCRIMINATIONS BY CARP 351

the S+ and the S nonresponse percentages [two-tailed two-sample t test assuming unequal variances contrasting themean difference between S and S+ nonresponse per-centages before and after the change 8 observations just be-fore the stimulus change vs 8 observations just after t(11) =277 p lt 019] This implies that the rather subtle artifactsin the original S had indeed been exploited as discrimi-nants

One oddity is the fact that although the stimuli changedsignificantly in Sessions 54 (second-generation S ) and62 (removal of the first note of S+ and S ) in each case

a pronounced anomaly in Ororsquos performance occurred inthe following session

Studies of melody discrimination in animals have oftenfound that the behavior was controlled by local featuressuch as timbre pitch register or the absolute pitch of the ini-tial note rather than by the melodic patterning per se(DrsquoAmato amp Salmon 1984 Hulse amp Cynx 1985 Hulseamp Page 1988 Poli amp Previde 1991) (In this paper for theterm local properties I follow the convention of referringnot only to features like distinctive individual notes whichare clearly local in a temporal sense but also to features

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 70

Session Number

S+

S-

= Piano= Down a fifth= wo 1st note= wo 1st 7 amp last 4 notes

S+S-ITI

Figure 13 Experiment 4 (melody discrimination) trials with no responses The MIDI timbre was violin except for 13 sessions ofpiano as marked The corrected S was introduced at Session 54 The first notes of S+ and S were removed at Session 62 The sixinitial and four final notes were removed at Session 69 Crosses denote silence

Figure 14 Experiment 4 (melody discrimination) all responses Sessions terminated with the S+ trial in which the 55th pel-let was dispensed Crosses denote silence

0

20

40

60

All

Pre

sses

0 10 20 30 40 50 60 70

Session Number

S+

S-

Oro

S+S-ITI

352 CHASE

like timbre and pitch register which although recogniz-able in any local segment can be constant over the dura-tion of the stimulus and which therefore might arguablybe called global properties) It should not be surprisingthat with sequential stimuli such as sound animals oftenexploit local features in preference to global pattern fea-tures In the acoustic domain features that are instantly rec-ognizable presumably confer a survival advantage not onlyon listeners but also on creatures in whose interest it is tobe identifiable by sounds they make Oro did not have tim-bre available as a discriminant but there is no conclusiveevidence that he did or did not use other local features andit is not known which if any global features he might haveused

It warrants mention that in this type of discriminationexperiment inaccurate responding need not imply that thesubject is musically insensitive because musical sensitiv-ity can actually confound discriminative accuracy if bothstimuli are musically plausible or stylistically similar In-deed throughout this experiment the stimuli were moni-tored through a speaker in the laboratory office and S+ andS became so familiar and the pitch-track-reversed Ssounded so pleasing that human observers occasionallybecame confused as to which reinforcement contingencywas in force in the tank

The finding that Oro did not need timbre cues to dis-criminate melodies contrasts sharply with the result in ratsreported by Poli and Previde (1991) Using as stimuli for-ward and pitch-track-reversed versions of the melodyldquoFregravere Jacquesrdquo they tested for discrimination on the basisof melodic pattern The rats had neither previous experi-mental experience nor prior familiarity with music In anattempt to preclude the exploitation of local features suchas the absolute pitch of distinctively positioned notes each15-sec stimulus presentation began at a randomly chosenposition within the melody Different groups of subjectswere asked to discriminate two melodic stimuli that dif-fered in melody only in timbre only or in both attributesHowever the stimuli were never heard as unitary melodiesfrom start to finish and were presented in a continuousstream of randomly sequenced exposures with responsesin the presence of S+ being reinforced only on an FR-5schedule This would seem to be such a formidable task asto make it unsurprising that animals failed except when tim-bre a consistent property of every note in each stimuluswas available as a discriminant However Poli and Previdedid suggest that rats might well prove able to discriminatemelodies without timbre cues under other conditions

CONCLUDING REMARKS

The distinction between local features and pattern fea-tures although it arose in connection with melody dis-crimination is equally relevant to the categorization ex-periment To say that in classifying music as blues orclassical the koi might have been responding to deepgeneric attributes is not to say that they were necessarilyusing anything other than local cues because the diag-

nostic property could have been a particular combinationof timbre loudness pitch brief rhythmic or melodic fig-ures and other such local features A human scanning aradio dial requires only a fraction of a second to identifythe genre of a given station hardly enough time for patternfeatures to manifest themselves so a brief sample of musiccould well contain something recognizable to an animalthat had a rote store of auditory feature memories Localfeatures might control classification behavior even whenthere is extensive exposure to a stimulus Conceivably an-imals could acquire a functional understanding of musicentirely on the basis of the distribution and frequency ofvarious combinations of essentially local features with-out regard to the artistic pattern features in terms of whichmusical genres are commonly defined

Prior to this series of experiments the prevailing opinionappeared to be skepticism as to whether koi could dis-criminate one piece of music from another under any cir-cumstances Now it appears that these animals can discrim-inate polyphonic music discriminate melodic patternsand even classify music by artistic genre As far as I knowthese experiments presented the most complex auditorystimuli to which fish have ever been shown capable ofmaking sophisticated discriminative responses Howeverthere remains the task of elucidating the stimulus controlfunctions of the constituents of that complexity such aspattern features local features and simple properties of thestimulus as a whole The present work was intended as ex-ploratory rather than explanatory and the results clearly ex-tend the known envelope of auditory capabilities in fish

REFERENCES

Baron M R (1965) The stimulus stimulus control and generaliza-tion In D I Mostovsky (Ed) Stimulus generalization (pp 62-71)Stanford CA Stanford University Press

Chase A R amp Hill W (1999) Reliable operant apparatus for fishAudio stimulus generator response button and pellet-dispensing nip-ple Behavior Research Methods Instruments amp Computers 31 470-478

Coombs S Jannsen J amp Montgomery J C (1992) Functional andevolutionary implications of peripheral diversity in lateral line sys-tems In D B Webster R R Fay amp A N Popper (Eds) The evolu-tionary biology of hearing (pp 267-294) New York Springer-Verlag

DrsquoAmato M R amp Salmon D P (1982) Tune discrimination in mon-keys (Cebus apella) and rats Animal Learning amp Behavior 10 126-134

DrsquoAmato M R amp Salmon D P (1984) Processing of complex au-ditory stimuli (tunes) by rats and monkeys (Cebus apella) AnimalLearning amp Behavior 12 184-194

Fay R R (1988) Hearing in vertebrates A psychophysics data-bookWinnetka IL Hill-Fay Associates

Fay R R (1992) Analytic listening in goldfish Hearing Research 59101-107

Fay R R (1994) Perception of temporal acoustic patterns by the gold-fish (Carassius auratus) Hearing Research 76 158-172

Fay R R (1995) Perception of spectrally and temporally complexsounds by the goldfish (Carassius auratus) Hearing Research 89146-154

Fay R R (1998) Auditory stream segregation in goldfish (Carassiusauratus) Hearing Research 120 69-76

Fay R R amp Ream T J (1986) Acoustic response and tuning in sac-cular nerve fibers of the goldfish (Carassius auratus) Journal of theAcoustical Society of America 79 1883-1895

Hartman W M (1988) Pitch perception and the segregation and inte-

MUSIC DISCRIMINATIONS BY CARP 339

stimuli and if so whether they can generalize to unfamiliarmusic from the same stylistic categories capabilities pre-viously demonstrated in pigeons by Porter and Neuringer(1984)

A standard demonstration of categorization behaviorbegins by training an animal to classify the members oftwo nonoverlapping sets of stimuli by responding only inthe presence of the members of one particular set Each setis an experimenter-defined category and each stimulus isan exemplar of one category The animal is said to havelearned the two categories if it then responds appropriatelyto novel exemplars of each and if there is reason to believethat it can also discriminate exemplars within each set aswell as between sets The latter criterion ensures that theanimal was perceiving categories rather than exhibitingcategorical perception that is the animalrsquos treating cer-tain exemplars alike must not be due merely to an inabil-ity to tell them apart (Herrnstein 1992 Sturdy PhillmorePrice amp Weisman 1999)

In visual categorization studies pigeons have beentrained to classify photographs according to whether theydo or do not contain people water fish aerial views of aparticular location tree leaves damaged by a particularspecies of caterpillar and other such complex criteria (Herrn-stein 1992) If intermittent reinforcement is used partic-ular exemplars might be repeated yet never associatedwith reinforcement if there is improvement in the accu-racy of classification of even these stimuli it is reason-able to conclude that the animal is responding to them onthe basis of features that imply membership in a specificcategory instead of as isolated stimuli The training setscan range from closed and repetitive stimuli with testingdone by using novel stimuli as probes to streams of con-tinually novel stimuli in which case classification accu-racy measures categorization behavior on an ongoingbasismdasheven under CRFmdashbecause rote memory (at leastof whole stimuli as opposed to features) can play no role(Malott amp Siddall 1972)

Categories can also be defined with no systematic rela-tionship to stimulus properties so that the only way to dis-

tinguish them is through rote memory of the reinforce-ment contingency associated with each exemplar Rotememory capacity in animals can be considerable Vaughanand Greene (1984) trained pigeons to sort visual imagesinto rote categories and found that they could easily mem-orize hundreds of pictures and remember them for at least2 years In foraging and food-hiding birds such as theHawaiian honeycreeper and Clarkrsquos nutcracker estimatesof the memory capacity for locations range well into thethousands (Herrnstein 1992)

The protocol in the present study used closed trainingsets and CRF but within-session repetition was almostnonexistent The first presentation of a pair of novel CDsconstituted a stream of novel stimuli and served as a mea-surement probe

Because of the prevailing skepticism that koi could dem-onstrate the capabilities I was hoping to find I tried to makeevery task as easy as possible for the animals a constraintthat dictated some procedural choices that might be re-garded as unconventional One example is the use of a freeoperant and CRF rather than discrete trials or a lean rein-forcement schedule Another is the use of reversals in-stead of extinction trials in order to demonstrate control bystimuli rather than by prevailing reinforcement contin-gency The rationale for CRF was to minimize stress andmaximize feedback given that the exertional cost of but-tonpressing appeared relatively high and that consequentlythe maximum possible response rate was expected to berelatively low Unlike a discrete-trials procedure the free-operant approach fixed each trialrsquos stimulus presentationtime while letting the numbers of responses and reinforce-ments vary My intention was to minimize interferencewith the formation of associations between the positivestimulus and the instantaneous conditioned reinforce-ment or the actual consumption of food With respect toelucidating the stimulus control I was concerned that aswitch to total extinction might cause excessive emotionalside effects and reduce the subjectsrsquo long-term viabilityTherefore in my experiments the usual role of extinctiontrials was played by reversals In a study with so few sub-

0

50

100

0 10 20 30 40

Beauty

S+

S-

Tri

als

wit

h N

o P

ress

0 10 20 30 40

Oro

S+

S-

0 10 20 30 40 Session Number

Pepi

S+

S-

Session NumberSession Number

Figure 3 Preliminary phase (sound vs silence) percentages of S+ and S intervals in which the fish did not press the button at allA comparatively high percentage of nonresponding for S indicates successful discrimination Crosses denote silence

340 CHASE

jects reversals can also act like counterbalancing in con-trolling for possible differences in familiarity and saliencywith respect to the stimuli designated as S+ or S Re-versals have the further advantage of offering glimpses ofadditional phenomenamdashin particular reversal learningper se

MethodThe protocol was an extension of that used in the preliminary

sound-versus-silence discrimination as described above Howevernow there were three kinds of intervalsmdashnamely S+ trials (bluesmusic) S trials (classical music) and a silent intertrial interval(ITI) Also the intervals were now of fixed duration 30 sec for S+and S sound trials and 15 sec for the ITI During the ITI a cor-rection procedure was programmed so that any response that oc-curred less than 10 sec before the silence was scheduled to end pro-longed the ITI by resetting the countdown timer to 10 sec Thesequence of S+ and S trials was randomized in real time but a ses-sion always began with two successive S+ trials and there could beno more than three consecutive trials with any one stimulus type Asession ended at the end of the full S+ interval during which the 50threinforcement was delivered

An important aspect of the procedure was that the computer didnot restart the piece of music at the beginning of each trial but in-stead resumed the CD where it had left off (unless there were fewerthan 30 sec of music remaining on that track in which case the stim-ulus would be the first 30 sec of the following track the intent beingto try to ensure that every stimulus would be a full 30 sec of music)Each of the S+ and S CDs contained roughly 120 distinct excerpts and a session ended with the S+ excerpt during which the 50th re-sponse was made so it was rare for a session to run long enough forany CD to start over and thus there was relatively little within-session repetition of stimuli Each excerpt was effectively a separatemini-piece in one of the two styles represented by the two CDsThus even within a single piece of music or CD track what the fishconfronted was essentially a categorization problem in contrast to adiscrimination between two brief musical fragments that would berepeated identically many times in each session Because the com-puter consistently divided a CD into the same sequence of fixed-length excerpts each time a musical CD was somewhat analogousto a tray containing 120 photographic slides as a source of exem-plars in a visual categorization experiment

Figure 4 summarizes the sequence of experimental conditions andthe recordings used starting with the preliminary sound-versus -silence phase The computer software allowed individual tracks to bemarked for exclusion and as is noted in the CD reference list intwo of the blues CDs certain tracks were excluded because they con-tained speech or silence

In the beginning of Experiment 1 (Sessions 40ndash55) the stimulussources were two entire CDs S+ was John Lee Hookerrsquos Blues Be-fore Sunrise (carried over from the sound-versus-silence discrimina-tion) and S was Bach oboe concertos (familiar from a priorstudy) Over the course of the first 6 sessions 2 fish showed no ev-idence of learning the discrimination whereas the 3rd achieved asuccess that proved short-lived Therefore I simplified the task byrestricting the stimuli to a single track from each CD The first suchpair of tracks was used for 30 sessions and over the next 15 sessionsthree new pairs of tracks were used each pair for 5 consecutive ses-sions After the animals had learned to discriminate a single classi-cal track from a single blues track these four times I again allowedthe stimuli to come from the entire CD of each genre

Because CRF was always in effect during S+ providing feedbackas well as reinforcement the best way to reveal whether the fish wereclassifying the music on the basis of a categorical principle ratherthan on the basis of rote memory was to present novel stimuli There-fore scattered throughout the experiment were nine probe sessions in

which both the S+ and the S CDs were novel These were Sessions115 120 131 138 152 157 163 168 and 177 The music was se-lected for diversity within the genre S+ included four different per-formersrsquo CDs plus five compilation CDs with more than 20 addi-tional blues performers S consisted of six baroque-style CDs andthree non-baroque composersmdashspecifically Mozart Beethovenand Schubert

The buttonpressing response involves a fishrsquos entire body sincethe fish must position itself over the button and essentially ram itTherefore such a response is inherently somewhat slowmdashfar slowerthan for example a birdrsquos peck at a key or a ratrsquos press of a lever Be-cause the fish typically would not hover over the button and becausethey appeared to commit to a response by swimming in from a dis-tance after each S+ interval the silent ITI began with a grace periodof 1 sec during which a buttonpress would still be counted and re-inforced on the assumption that the response had begun during S+

During Sessions 147ndash149 the 200-Hz high-pass filter was turnedon in order to minimize stimulation of the lateral line The idea wasto try to ensure that the discrimination between blues and classicalwould be made on the basis of input from the fishrsquos inner ears thesensory system presumably most capable of detecting the f ine-grained acoustic features of music that form the basis for stylisticdistinctions by humans

The possibility of acoustic artifacts owing to hardware was testedby a control procedure in which the blues and the classical CDs wereeach loaded into the drive programmed for the other (Sessions 182ndash238) The effect was to reverse the definitions of S+ and S (ie toreinforce responses to classical music but not to blues) This was ex-pected to produce a dramatic decrement in accuracy which woulddemonstrate that responding had indeed been under the control ofthe musical content of the S+ and S channels

Results and DiscussionThe use of CRF imposed the obligation to verify that

the subjects were discriminating the stimuli and notmerely the current state of the multiple CRF-extinctionschedule Proof that a subject was not being cued by feed-back from routine test responses would be a statisticallysignificant difference between the percentages of S andS+ trials in which the subject did not press the button atall Such a finding would allow rejection of the hypothe-sis that the subject had been testing the button equally dur-ing both stimulus conditions The alternative hypothesis isdirectional in that beyond exhibiting a difference per sean auditorily discriminating subject would be expected toignore the response button more during S than during S+Therefore unless otherwise specified throughout thispaper significance is reported in terms of the p value of aone-tailed paired t test (Microsoft Excel 97 SR-1) on thenonresponse percentages associated with the two stimulustypes in each of n sessions the alpha level used was 05

As is indicated graphically in Figures 5 and 6 all 3 koidiscriminated blues from classical music and this behav-ior generalized into an ability to classify unfamiliar ex-emplars by genre [for each of the 3 subjects 9 probe ses-sions t(8) gt 10 p lt 001] To my knowledge this is thefirst demonstration in fish of open-ended categorization(Herrnstein 1992) and of any kind of categorization withauditory stimuli

Figure 5 shows the percentages of S+ and S trials inwhich there was no responding In Session 115 the firstprobe Beauty responded only during S+ and not at all dur-

MUSIC DISCRIMINATIONS BY CARP 341

ing S or ITI In Probe Session 138 the novel S was Vi-valdi guitar music which proved to raise problems Figure 6shows all the responses for each session note the higherS response rate at Session 138 Session 182 was the first

control-by-reversal session Sessions 138 and 182 are fur-ther discussed below

The data from the probe sessions are plotted in Figure 7and are shown in historical context in Figure 5 Figure 7

Figure 4 Experiments 1 and 2 (categorization and iterated reversals) stimulus chart Each column representsa single stimulus CD which is identified by text that starts in that column at the bottom of the figure Each rowrepresents a group of sessions Bullets indicate the CDs presented in their entirety as the S+ and S in each ses-sion group whereas the numbers associated with Sessions 56ndash100 identify the specific CD tracks used as stim-uli A triple bullet marks the first presentation of a given CD a single bullet denotes a stimulus heard previ-ously Rows in which both stimuli are represented by triple bullets denote groups of sessions in which the firstone exposed the subject to all-novel stimuli and thus served as a probe session

342 CHASE

also shows means for the nonprobe and the probe sessionsin the session range 115ndash181 The fish classified musicwith which they had had no training about as accurately asthey classified familiar training stimuli This generaliza-tion to unfamiliar exemplars demonstrates that the fishwere not relying on rote memory but were instead exhibit-ing open-ended categorization (Herrnstein 1992)

To assess whether the fish were exhibiting true percep-tion of categories preclusion of categorical perception(ie the inability to discriminate exemplars within a cat-egory) was necessary The great complexity of musicalstimuli renders likely the existence of a mix of feature di-mensions on the basis of which a sample only a few sec-onds long suffices to distinguish any two pieces or evendifferent performances of the same piece The blues stim-uli ranged from John Lee Hooker to Sonny Boy William-son and the classical ranged from baroque to Schubertboth categories featured a variety of ensembles It is im-plausible that recordings that sound so very different tohumans would be completely indistinguishable to thesefish The result of Experiment 4 below provides strongadditional evidence Koi can discriminate generically simi-lar melodies which implies that they can discriminategenerically similar recordings that differ along a multi-plicity of dimensions of which melody is only one

In Figures 5 and 6 the data for Sessions 182ndash192 showthe disruption of performance following the reversal of thereinforcement contingencies This reversal served as acontrol procedure the result of which confirmed that re-sponding was indeed under the control of the musical con-tent as opposed to any electronic artifact in the S+ andS audio channels

In Sessions 138ndash144 the fish had unexpected difficultydiscriminating Vivaldi guitar concertos from a blues com-pilation Although it is plausible that the fish could havelearned that guitar sounds were characteristic of blues theguitar concertos arguably did not sound to humans as muchlike blues as like the Vivaldi cello concerto which was theprevious S and which the fish had had no trouble dis-tinguishing from blues Another possible source of confu-sion for the f ish was the fact that this S+ was the firstcompilation CD to be presented as a stimulus Thus the di-versity of blues styles distinguished this S+ CD from anyprevious one Given the fishesrsquo problem with this dis-crimination I paired the Vivaldi guitar concertos with somevery familiar John Lee Hooker (Sessions 145ndash146) Whendiscrimination did not improve I left these stimuli in placebut turned on the 200-Hz high-pass filter for three ses-sions (147ndash149) As can be seen from Figure 5 the resultof turning on the filter was an immediate improvement inperformance which persisted after the filter was turnedoff Apparently these particular stimuli were salient andhad similar features in the lower frequencies which con-fused the fish until the high-pass filter forced them to at-tend to higher frequency features on the basis of whichthe music was more readily discriminable It would alsoappear that the lateral line was not necessary for the dis-crimination of familiar music As DrsquoAmato and Salmon

(1982) noted ldquoIndividuals do not always rely on the sameproperty of the stimulus and may according to circum-stances shift their reliance from one feature to anotherrdquo(p 130) (In any case Vivaldi evidently can impress listen-ers in odd ways Porter amp Neuringer 1984 reported thata Vivaldi violin concerto sounded more like Stravinsky thanlike Bach to their pigeons as it did also to some humans)

Even a convincing demonstration of categorization canfail to identify the stimulus features that exert control atany given time especially if the stimuli are complex In par-ticular there can be uncertainty as to whether classificationbehavior had been under the stimulus control of the fea-tures in terms of which the experimenter had defined thecategories or whether the subjects had discovered an ef-fective discriminant of which the experimenter was unawareThe diversity of S+S pairings (see Figure 4) presum-ably rules out the possibility that the fish could have beenrelying on only a single discriminant such as timbre buta constant concern is the possible existence of a simple at-tribute that would have allowed the subjects merely to dis-criminate instead of categorizing In the present experi-ment the choices of stimuli and control procedures wereintended to ensure that all the available discriminants weresufficiently complex For example even if a fish used asthe discriminant the sound of a human voice which waspresent in virtually all of the blues but in none of the clas-sical the diversity of singing voices would imply open-ended categorization nonetheless

The possibility that the fish memorized individual or re-curring features cannot be ruled out An animal probablydoes exploit a collection of memorized features alongwith various abstracted properties It would be surprisingif no features at all were salient enough to be rememberedand one wonders whether it is even possible to abstract acategorical discriminant without having particular fea-tures in memory at least temporarily

The notion that koi might classify blues and classicalmusic on the basis of deeper generic attributes is supportedby the results of experiments reported below which indi-cate that timbre cues are not required Porter and Neuringer(1984) trained pigeons to discriminate baroque from mod-ern music using initial exemplars that could have been al-ternatively classified as organ and orchestral music but theeffective discriminant turned out to be something otherthan instrumental timbre In a recent report (Watanabe ampSato 1999) Java sparrows learned to discriminate pianomusic by Schoumlnberg from piano music by Bach and theythen correctly classified orchestral music as Schoumlnberg-like or Bach-like whether written by those two composersor by Carter and (even) Vivaldi Studies that analyze the per-ceptual world of pigeons in terms of multidimensionalscaling spaces reveal that the birds learn enough aboutnonexemplars to form a distinct category for them as wellas for exemplars In other words pigeons appear to eval-uate a stimulus not only as possibly a good exemplar but alsoas a good nonexemplar which is more work than binaryclassification logically requires (Herrnstein 1994) Giventhat the more features of the environment to which one is

MUSIC DISCRIMINATIONS BY CARP 343

sensitive the more information is available from which todiscern patterns and changes indications that animalslearn more than the minimal solution to classificationproblems involving complex stimuli suggest that as com-pared with trying to ignore as much as possible of theworld evolution favors embracing its complexity

EXPERIMENT 2 Iterated Reversals

MethodThe first categorization session in which the contingencies were

reversed had served as a control procedure This experimental con-

0

25

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75

100

Tri

als

wit

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ress

Beauty

S-

S+

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100

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ress

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S+

200 Hz filter

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Tri

als

wit

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ress

40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

Session Number

Pepi

S+

S-

S+ S- ITI

Figure 5 Experiment 1 (categorization) percentages of S+ (blues) and S (classical) trials and intertrial intervals (ITIs silence)during which the fish did not press the button at all plotted for each session The greater the separation between a sessionrsquos S+ andS nonresponse percentages the more clearly the subject was discriminating the stimuli as opposed to responding indiscriminatelyand receiving feedback from the reinforcement contingency The boxed data points indicate probe sessions The bar from Sessions147ndash149 shows where the 200-Hz low-frequency cutoff filter was used The circled data points (Session 182) indicate the first control-by-reversal session In the reversal sessions (182ndash192) S+ (still represented by open squares) was now classical music whereas S (stillrepresented by filled triangles) was blues Crosses denote silence

344 CHASE

dition (ie with blues now the S and classical now the S+) wasthen extended into an iterated-reversal experiment The primary goalwas to test koi in reversal learning with complex auditory stimuliafter having found nothing in the literature on the subject of auditoryreversal learning in fish

A secondary goal was to prepare for a planned experiment with aclassification procedure involving two visually distinct buttons withresponses on a particular button to be reinforced only in the presenceof a particular type of music The rim of the original button had beenmachined from black Delrin A new rim was made from an ivory-

colored blank of the same plastic and installed after six sessions ofthe unsignaled reversal (ie no change in the button) Thereafterrim color alternated in synchrony with contingency reversals withblack and ivory signaling that S+ was blues and classical respec-tively The fish would experience a total of four color changes thefirst of which did not signal a contingency change

The sessions were terminated by either the trial in which the 50thpellet was dispensed or an elapsed time of 90 min whichever camefirst Altogether there were 119 sessions spanning four reversals(see Figure 4)

Figure 6 Experiment 1 (categorization) all responses Number of responses in each session during blues trials classical trials andintertrial intervals (ITIs) Under the reversal condition that began with Session 182 blues became S and classical became S+ Bluesresponse counts above 50 reflect the onset of extinction Reversal sessions in which the classical response count was less than 50 wereterminated at 90 min Crosses denote silence

0

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All

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sses

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Pepi

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120

All

Pre

sses

ITI

Oro

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All

Pre

sses

BeautyBluesClassicalITI

MUSIC DISCRIMINATIONS BY CARP 345

Just before the first reversal the stimuli had been a House of Bluescompilation (S+) and a baroque horn compilation (S ) When thecontingencies were reversed making blues S and classical S+both stimuli were also replaced The first reversal stimuli were Bachoboe concertos (S+) and John Lee Hookerrsquos Real Folks Blues (S )both very familiar to the fish In the next three phases of the first re-versal three additional pairs of familiar CDs were used In the fifthand final phase of the first reversal the fish were exposed to entirelynovel stimuli (S The Blues Story compilation S+ Bach triosonatas) As in the categorization study the first session with novelstimuli (Session 224) served as a probe testing for open-ended cat-egorization Blues and classical successively exchanged roles as S+and S in three additional reversal phases all using familiar stim-uli As can be seen in Figure 4 when the first and third reversals oc-curred at least one stimulus CD changed as well The final reversalbrought the contingencies back to where they had been before thefirst reversalmdashnamely with blues as S+ and classical as S

ResultsThe first reversal (Session 182) produced considerable

behavioral disruption and erroneous responding (see Fig-

ures 8 and 9) In the first 6ndash9 sessions the increase in re-sponding to the genre newly become S+ was insufficientfor any fish to earn 50 reinforcements within the 90-mintime limit (Figure 8) Beauty and Oro steadily improvedand were reliably discriminating by the 16th and 23rd ses-sions respectively Pepi achieved significance by Session 9but then his performance was substandard until Session 27[5 sessions ts(4) gt 229 p lt 010 p lt 009 and p lt 042respectively] Near the end of the first reversal the probesession (224) revealed that the classification behavior ex-hibited by Beauty and Oro was clearly open-ended catego-rization With each successive reversal it took fewer sessionsfor Beauty and Oro to demonstrate clear discrimination(Figures 9 and 10) Even Pepi eventually learned each re-versalmdashalbeit while continuing to call attention to the ex-istence of considerable and systematic individual differ-ences among fish In Figure 9 least-squares regressionlines are plotted for S nonresponse data and as is shownin Figure 10 their slopes indicate improvement rates of

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Mean 115 120 131 138 152 157 163 168 177 Mean

Probe Sessions (Novel CDs) Probes

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als

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ress

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als

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o P

res

s

Figure 7 Experiment 1 (categorization) categorization performance during probe ses-sions (ie all-novel stimuli) percentages of S+ trials intertrial intervals (ITI) and S tri-als in which the fish did not respond Black bars indicate S+ gray bars indicate S andwhite bars indicate ITI Low nonresponse percentages for S+ indicate a high likelihoodof responding during S+ whereas high nonresponse percentages for S indicate that thefish tended to ignore the button during S The leftmost ldquoMeanrdquo bars show the averagesof all the nonprobe sessions in the session range 115ndash181 and the rightmost ldquoMeanrdquo barsshow the averages of the probe sessions

346 CHASE

08 and 11 per session for Beauty and Oro respec-tively during the first reversal (Sessions 182ndash238) Overthe final 5 sessions of each reversal phase discriminationby Beauty Oro and Pepi was statistically significant at

levels always better than p lt 010 p lt 016 and p lt 042respectively [ts(4) gt 229] It can be seen in Figure 8 thatwith each reversal the increase in responding to the new S+was generally faster than the extinction to the former S+

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150 175 200 225 250 275 300

Pepi

classical

BluesClassical

Figure 8 Experiment 2 (iterated reversals) counts of all responses by session Note that in graphs of reversal data the symbols con-sistently indicate genre (open squares blues filled triangles classical) not stimulus semantics (S+ or S ) which of course change ateach reversal This convention highlights the fluctuating response pattern associated with each genre longitudinally as successive re-versals of reinforcement contingency produce disruption and then learning with increasing efficiency The primary session termina-tion trigger was the trial on which the 50th pellet was delivered but in the early sessions of the first reversal no subject made as manyas 50 ldquocorrectrdquo responses to the former S within the session time limit even while responding many more than 50 times without re-inforcement to the former S+ Note that the extinction-induced response frenzy associated with a genrersquos suddenly becoming S de-creases with each reversal Crosses denote silence

MUSIC DISCRIMINATIONS BY CARP 347

EXPERIMENT 3Transition to Synthetic Keyboard Music and

Polyphonic Discrimination with Identical Timbre

The next step was to try to extend the learned classifi-cation of natural music to MIDI (Musical Instrument Dig-

ital Interface) synthesized music in which S+ and Swere not distinguishable by timbre

MethodPretraining After the iterated-reversal experiment the fish re-

mained in the homeexperimental tank from which all the appara-tus had been removed and they were not exposed to music or to anytraining or experimental procedures for a period of 10 months The

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als

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0

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classical

blues

classical

classical

blues

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wit

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ress

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100

150 200 250 300

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Pepi

0

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50

75

100

First Reversal

Beauty

Probe

Tri

als

wit

h N

o P

ress

ITI

BluesClassicalITI

Figure 9 Experiment 2 (iterated reversals) percentages of trials with no responses by session Note the increasingly efficient learn-ing of nonresponding to each former S+ as shown by the increasing slopes of the least-squares regression lines Session 224 (dashedline) was a probe the accurate discrimination of entirely novel stimuli indicates that the fish were performing open-ended catego-rization Crosses denote silence

348 CHASE

work resumed with a reintroduction to the apparatus and protocol asleft off at the end of the fourth and final reversalmdashthat is with S+and S being blues and classical respectively However the fishwere also being prepared to encounter the synthetic stimuli that werebeing created at that time which consisted of a single short piecefrom each genre rather than a collection comparable in duration andvariety with the commercial CDs used previously Therefore in pre-training the stimuli were the same two CDs the subjects had lastheard (see Figure 4 Session 300) but only a single track from eachS was an excerpt from a Bach oboe concerto S+ was the John LeeHooker song ldquoOne Bourbon One Scotch and One Beerrdquo of whicha synthesized version was in the works

Initially Beauty and Oro seemed to manifest effects of the longhiatus in the form of low response rates (not enough to earn 50 pel-lets in a session) and some transient difficulties operating the buttonand taking pellets from the nipple However even allowing for somerelearning and the reduced size of the new stimuli the immediacywith which all 3 subjects exhibited highly accurate discriminationsuggests that the original discrimination training had been retained(compare the leftmost sessions in Figure 11 with the rightmost inFigure 9)

Procedure The new stimuli were musically simplif ied MIDIkeyboard renditions of music of the types the f ish had alreadylearned to classify S+ was the familiar blues song described aboveand S was the unfamiliar Fugue 2 from Book I of Bachrsquos Well-Tempered Clavier To minimize the presence of extraneous cues allthe performances were done by the same musician with the sameequipment (a Kurzweil Model k2000vp keyboard Young Chang Re-search and Development Institute Waltham MA) the same se-quencing software (Studio Vision Pro Version 40 Opcode SystemsNashville TN) and the same settings for volume and for timbre(acoustic piano) Because the new stimuli were so short that theywould repeat after only a few trials rote memory could play a rolein their discrimination and thus the operative level of stimulus con-trol was being allowed to potentially regress from categorization todiscrimination

The initial synthetic stimuli turned out to trigger a deteriorationin classification accuracy (Figure 11 Session 13) It seemed possi-ble that this was an artifact of the musical translation process be-cause even humans had some difficulty recognizing the John LeeHooker song in synthetic form It had gone from bluesy to bouncyits original bass inflections were absent and there was no melodicvoice comparable with that of the singer Therefore at Session 24 Iintroduced a second generation of stimuli S+ remained the samepiece but the performance was somewhat more faithful to themodel The old S (the Bach fugue) had been much shorter than S+and thus had been repeating more often so it was replaced by a syn-

thesized rendition of the f irst movement of Vivaldirsquos ConcertoGrosso in A minor Opus 3 No 6 whose duration more closelymatched that of S+ In addition the timbre of the blues was changedfrom acoustic piano to rock piano thus adding timbre as an availablediscriminant However from Session 47 until the end of the experi-ment S+ and S again had timbre in common specifically rockpiano (starting in Session 47) chiffloot (starting in Session 55) andguitar (starting in Session 62)

ResultsWith the first presentations in a synthetic timbre discrim-

ination accuracy deteriorated (Figure 11 Sessions 13ndash23)perhaps because the first synthetic S+ was not a good enoughexemplar of the blues genre Pepi essentially ceased re-sponding during this time and had to be dropped from thestudy Starting at Session 24 with improved stimuli and adifference in timbre between S+ and S the behavior ofboth remaining subjects immediately changed and there-after their discriminative accuracy improved continually

When S+ and S were again made identical in timbre(Session 47) accurate classification persisted despite aperformance decrement probably related to the loss of asalient cue When the same pair of MIDI sequences waspresented in additional timbres generalization of accurateclassification to the new sounds appeared seamless The datafrom Session 47 and onward demonstrate [Sessions 18ts(17) gt 16 ps lt 001] that koi are capable of discriminat-ing polyphonic music on the basis of features other thanthe timbre of individual tone sources

EXPERIMENT 4 Discrimination of Melodies

Without Timbre Cues

After observing that instrumental timbre seemed not tobe a necessary discriminant in polyphonic music I inves-tigated whether timbre was necessary for koi to discrimi-nate single-voice musicmdashthat is melodies

MethodIn order to familiarize the subjects with the S+ melody and also

in hopes of rehabilitating Pepi this experiment began with severalsessions of collective exposure to a sound-versus-silence contin-gency CRF signaled by the music that would later be the S+ in thesound-versus-sound discrimination alternated with extinction sig-naled by silence In this group pretraining Pepi was observed bothpressing the button and taking pellets from the nipple but when sub-sequently isolated for melody discrimination sessions he consis-tently shied away from the nipple and again had to be dropped as asubject

The stimuli for the melody discrimination experiment (Figure 12)were all derived from the theme from Paganinirsquos 24th Caprice forsolo violin which is perhaps best known from Rachmaninoff rsquosldquoRhapsody on a Theme by Paganinirdquo S+ was the original melody asperformed on the MIDI keyboard S was derived from S+ by usingthe transformation described by Poli and Previde (1991) By using acomputer to modify the MIDI score S+rsquos order of pitches was re-versed whereas its original order of note durations was retained Inother words the first note of S got the duration of S+rsquos first notebut the pitch of S+rsquos last note the second note of S got the durationof S+rsquos second note but the pitch of S+rsquos next-to-last note and so onThis procedure can be thought of as retaining the rhythm track while

0

1

2

3S

lop

e (

ch

ang

ese

ssio

n)

1 2 3 4

Reversal Number

OroBeauty

Pepi

Figure 10 Experiment 2 (iterated reversals) improvementtrends For Beauty and Oro the improvement rate (Figure 9 re-gression line slopes percentage of nonresponse S trials per ses-sion) increases with each reversal

MUSIC DISCRIMINATIONS BY CARP 349

reversing the pitch track The result is two stimuli that are ldquoidenticalwith respect to their mean frequency note duration and rhythm butnoticeably different in their melodic patternsrdquo (Poli amp Previde 1991p 12) Such a pitch-track-reversed melody differs from a completelybackwards melody only in rhythm sacrificing the linkage betweeneach pitch and its original duration in order to preserve the originalsequence of durations per se (If the original melodymdashunlike the

Rachmaninoffmdashhas a palindromic rhythm track the pitch-track -reversed melody and the completely backwards melody are identical)The melodies were recorded using the same MIDI apparatus as thatdescribed above To enhance clarity the tempo was somewhat slowerthan that of the usual piano performance

Over the course of 53 sessions the instrumental timbre alternatedsix times between strings and acoustic piano but in any given ses-

0

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S+

ITI

S-

Beauty

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100

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S+

ITI

S-

Oro

Same Timbre Different Timbre Same Timbre

S+S-ITI

Pepi ceased responding

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0 10 20 30 40 50 60 Session Number

S+

ITI

S-

Pepi

Figure 11 Experiment 3 (transition to MIDI and timbre study) percentages of S+ and S trials dur-ing which the fish did not press the button During the first 12 sessions the stimuli consisted of a singletrack from each of the two commercial recordings the subjects had last heard 10 months earlier at theconclusion of the iterated-reversal experiment the immediate resumption of accurate discrimination sug-gests long-term memory of training The circled data points (Sessions 13 and 24) indicate the introduc-tion of the first- and second-generation synthetic music From Session 47 until the end of the experimentS+ and S had identical timbre each boxed data point pair indicates the first presentation of a new tim-bre Session 47 rock piano Session 55 chiffloot and Session 62 guitar Crosses denote silence

350 CHASE

sion S+ and S always had the same timbre The discrimination pro-tocol was unchanged from the previous experiments except that thesession termination trigger was raised from 50 to 55 pellets As a pre-liminary test for a possible perceptual invariance (Hulse Takeuchi ampBraaten 1992) S+ was transposed down a fifth in Sessions 51ndash52

After 53 sessions it was discovered that the MIDI technology hadintroduced artifactual differences between S+ and S A musicallyattuned visitor to the lab detected minor variations in note durationsbetween the two stimuli which apparently had resulted from incor-rect handling of the attackndashsustainndashdecay envelopes of S+rsquos recordednotes There also turned out to be subtle volume differences whichwere said to have resulted from the combination of the MIDI scoreediting process and the volume compression function in the digitalaudio tape (DAT) recorder used to create stimulus master tapesThese differences were confirmed by careful examination of thewaveforms using a computer oscilloscope Therefore a second gen-eration of S was created by direct numerical substitution of the S+pitches into the MIDI score in reverse order and by recording a newmaster tape with all volume compression disabled The correctionswere verified by waveform analysis

After eight sessions with the second-generat ion S both S+ andS were shortened by the removal of each onersquos distinctive initial noteand seven sessions later they were further shortened by the removal oftheir remaining initial six and final four notes The purpose of thesestimulus contractions was to look for behavioral disruption that might

indicate that the subject had been discriminating the melodies on thebasis of such local features as the absolute pitch of the initial note

Results and DiscussionBeautyrsquos performance inexplicably deteriorated to the

point where he had to be dropped as a subjectFigures 13 and 14 report the performance of Oro the only

fish to complete the melody experiment The data showthat without timbre cues Oro clearly discriminated betweenthe two melodies [in each stimulus condition (ie second-generation S first-note-removed and both-ends-clipped)5 final sessions t(4) gt 10 p lt 001]

Oro responded more to S+ than to S even in the veryfirst session with melodic stimuli Familiarization with theS+ during pretraining could well have contributed to thisresponse bias perhaps partly because music heard in asound-versus-silence context had consistently become theS+ in a subsequent sound-versus-sound discriminationHowever the MIDI artifacts in the first-generation stim-uli might also have played a role

Session 54 in which the corrected S was introducedmarks a significant reduction of the separation between

Figure 12 Experiment 4 (melody discrimination) musical scores of the normal (S+) and pitch-reversed (S )melodies

MUSIC DISCRIMINATIONS BY CARP 351

the S+ and the S nonresponse percentages [two-tailed two-sample t test assuming unequal variances contrasting themean difference between S and S+ nonresponse per-centages before and after the change 8 observations just be-fore the stimulus change vs 8 observations just after t(11) =277 p lt 019] This implies that the rather subtle artifactsin the original S had indeed been exploited as discrimi-nants

One oddity is the fact that although the stimuli changedsignificantly in Sessions 54 (second-generation S ) and62 (removal of the first note of S+ and S ) in each case

a pronounced anomaly in Ororsquos performance occurred inthe following session

Studies of melody discrimination in animals have oftenfound that the behavior was controlled by local featuressuch as timbre pitch register or the absolute pitch of the ini-tial note rather than by the melodic patterning per se(DrsquoAmato amp Salmon 1984 Hulse amp Cynx 1985 Hulseamp Page 1988 Poli amp Previde 1991) (In this paper for theterm local properties I follow the convention of referringnot only to features like distinctive individual notes whichare clearly local in a temporal sense but also to features

0

25

50

75

100

Tri

als

wit

h N

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ress

0 10 20 30 40 50 60 70

Session Number

S+

S-

= Piano= Down a fifth= wo 1st note= wo 1st 7 amp last 4 notes

S+S-ITI

Figure 13 Experiment 4 (melody discrimination) trials with no responses The MIDI timbre was violin except for 13 sessions ofpiano as marked The corrected S was introduced at Session 54 The first notes of S+ and S were removed at Session 62 The sixinitial and four final notes were removed at Session 69 Crosses denote silence

Figure 14 Experiment 4 (melody discrimination) all responses Sessions terminated with the S+ trial in which the 55th pel-let was dispensed Crosses denote silence

0

20

40

60

All

Pre

sses

0 10 20 30 40 50 60 70

Session Number

S+

S-

Oro

S+S-ITI

352 CHASE

like timbre and pitch register which although recogniz-able in any local segment can be constant over the dura-tion of the stimulus and which therefore might arguablybe called global properties) It should not be surprisingthat with sequential stimuli such as sound animals oftenexploit local features in preference to global pattern fea-tures In the acoustic domain features that are instantly rec-ognizable presumably confer a survival advantage not onlyon listeners but also on creatures in whose interest it is tobe identifiable by sounds they make Oro did not have tim-bre available as a discriminant but there is no conclusiveevidence that he did or did not use other local features andit is not known which if any global features he might haveused

It warrants mention that in this type of discriminationexperiment inaccurate responding need not imply that thesubject is musically insensitive because musical sensitiv-ity can actually confound discriminative accuracy if bothstimuli are musically plausible or stylistically similar In-deed throughout this experiment the stimuli were moni-tored through a speaker in the laboratory office and S+ andS became so familiar and the pitch-track-reversed Ssounded so pleasing that human observers occasionallybecame confused as to which reinforcement contingencywas in force in the tank

The finding that Oro did not need timbre cues to dis-criminate melodies contrasts sharply with the result in ratsreported by Poli and Previde (1991) Using as stimuli for-ward and pitch-track-reversed versions of the melodyldquoFregravere Jacquesrdquo they tested for discrimination on the basisof melodic pattern The rats had neither previous experi-mental experience nor prior familiarity with music In anattempt to preclude the exploitation of local features suchas the absolute pitch of distinctively positioned notes each15-sec stimulus presentation began at a randomly chosenposition within the melody Different groups of subjectswere asked to discriminate two melodic stimuli that dif-fered in melody only in timbre only or in both attributesHowever the stimuli were never heard as unitary melodiesfrom start to finish and were presented in a continuousstream of randomly sequenced exposures with responsesin the presence of S+ being reinforced only on an FR-5schedule This would seem to be such a formidable task asto make it unsurprising that animals failed except when tim-bre a consistent property of every note in each stimuluswas available as a discriminant However Poli and Previdedid suggest that rats might well prove able to discriminatemelodies without timbre cues under other conditions

CONCLUDING REMARKS

The distinction between local features and pattern fea-tures although it arose in connection with melody dis-crimination is equally relevant to the categorization ex-periment To say that in classifying music as blues orclassical the koi might have been responding to deepgeneric attributes is not to say that they were necessarilyusing anything other than local cues because the diag-

nostic property could have been a particular combinationof timbre loudness pitch brief rhythmic or melodic fig-ures and other such local features A human scanning aradio dial requires only a fraction of a second to identifythe genre of a given station hardly enough time for patternfeatures to manifest themselves so a brief sample of musiccould well contain something recognizable to an animalthat had a rote store of auditory feature memories Localfeatures might control classification behavior even whenthere is extensive exposure to a stimulus Conceivably an-imals could acquire a functional understanding of musicentirely on the basis of the distribution and frequency ofvarious combinations of essentially local features with-out regard to the artistic pattern features in terms of whichmusical genres are commonly defined

Prior to this series of experiments the prevailing opinionappeared to be skepticism as to whether koi could dis-criminate one piece of music from another under any cir-cumstances Now it appears that these animals can discrim-inate polyphonic music discriminate melodic patternsand even classify music by artistic genre As far as I knowthese experiments presented the most complex auditorystimuli to which fish have ever been shown capable ofmaking sophisticated discriminative responses Howeverthere remains the task of elucidating the stimulus controlfunctions of the constituents of that complexity such aspattern features local features and simple properties of thestimulus as a whole The present work was intended as ex-ploratory rather than explanatory and the results clearly ex-tend the known envelope of auditory capabilities in fish

REFERENCES

Baron M R (1965) The stimulus stimulus control and generaliza-tion In D I Mostovsky (Ed) Stimulus generalization (pp 62-71)Stanford CA Stanford University Press

Chase A R amp Hill W (1999) Reliable operant apparatus for fishAudio stimulus generator response button and pellet-dispensing nip-ple Behavior Research Methods Instruments amp Computers 31 470-478

Coombs S Jannsen J amp Montgomery J C (1992) Functional andevolutionary implications of peripheral diversity in lateral line sys-tems In D B Webster R R Fay amp A N Popper (Eds) The evolu-tionary biology of hearing (pp 267-294) New York Springer-Verlag

DrsquoAmato M R amp Salmon D P (1982) Tune discrimination in mon-keys (Cebus apella) and rats Animal Learning amp Behavior 10 126-134

DrsquoAmato M R amp Salmon D P (1984) Processing of complex au-ditory stimuli (tunes) by rats and monkeys (Cebus apella) AnimalLearning amp Behavior 12 184-194

Fay R R (1988) Hearing in vertebrates A psychophysics data-bookWinnetka IL Hill-Fay Associates

Fay R R (1992) Analytic listening in goldfish Hearing Research 59101-107

Fay R R (1994) Perception of temporal acoustic patterns by the gold-fish (Carassius auratus) Hearing Research 76 158-172

Fay R R (1995) Perception of spectrally and temporally complexsounds by the goldfish (Carassius auratus) Hearing Research 89146-154

Fay R R (1998) Auditory stream segregation in goldfish (Carassiusauratus) Hearing Research 120 69-76

Fay R R amp Ream T J (1986) Acoustic response and tuning in sac-cular nerve fibers of the goldfish (Carassius auratus) Journal of theAcoustical Society of America 79 1883-1895

Hartman W M (1988) Pitch perception and the segregation and inte-

340 CHASE

jects reversals can also act like counterbalancing in con-trolling for possible differences in familiarity and saliencywith respect to the stimuli designated as S+ or S Re-versals have the further advantage of offering glimpses ofadditional phenomenamdashin particular reversal learningper se

MethodThe protocol was an extension of that used in the preliminary

sound-versus-silence discrimination as described above Howevernow there were three kinds of intervalsmdashnamely S+ trials (bluesmusic) S trials (classical music) and a silent intertrial interval(ITI) Also the intervals were now of fixed duration 30 sec for S+and S sound trials and 15 sec for the ITI During the ITI a cor-rection procedure was programmed so that any response that oc-curred less than 10 sec before the silence was scheduled to end pro-longed the ITI by resetting the countdown timer to 10 sec Thesequence of S+ and S trials was randomized in real time but a ses-sion always began with two successive S+ trials and there could beno more than three consecutive trials with any one stimulus type Asession ended at the end of the full S+ interval during which the 50threinforcement was delivered

An important aspect of the procedure was that the computer didnot restart the piece of music at the beginning of each trial but in-stead resumed the CD where it had left off (unless there were fewerthan 30 sec of music remaining on that track in which case the stim-ulus would be the first 30 sec of the following track the intent beingto try to ensure that every stimulus would be a full 30 sec of music)Each of the S+ and S CDs contained roughly 120 distinct excerpts and a session ended with the S+ excerpt during which the 50th re-sponse was made so it was rare for a session to run long enough forany CD to start over and thus there was relatively little within-session repetition of stimuli Each excerpt was effectively a separatemini-piece in one of the two styles represented by the two CDsThus even within a single piece of music or CD track what the fishconfronted was essentially a categorization problem in contrast to adiscrimination between two brief musical fragments that would berepeated identically many times in each session Because the com-puter consistently divided a CD into the same sequence of fixed-length excerpts each time a musical CD was somewhat analogousto a tray containing 120 photographic slides as a source of exem-plars in a visual categorization experiment

Figure 4 summarizes the sequence of experimental conditions andthe recordings used starting with the preliminary sound-versus -silence phase The computer software allowed individual tracks to bemarked for exclusion and as is noted in the CD reference list intwo of the blues CDs certain tracks were excluded because they con-tained speech or silence

In the beginning of Experiment 1 (Sessions 40ndash55) the stimulussources were two entire CDs S+ was John Lee Hookerrsquos Blues Be-fore Sunrise (carried over from the sound-versus-silence discrimina-tion) and S was Bach oboe concertos (familiar from a priorstudy) Over the course of the first 6 sessions 2 fish showed no ev-idence of learning the discrimination whereas the 3rd achieved asuccess that proved short-lived Therefore I simplified the task byrestricting the stimuli to a single track from each CD The first suchpair of tracks was used for 30 sessions and over the next 15 sessionsthree new pairs of tracks were used each pair for 5 consecutive ses-sions After the animals had learned to discriminate a single classi-cal track from a single blues track these four times I again allowedthe stimuli to come from the entire CD of each genre

Because CRF was always in effect during S+ providing feedbackas well as reinforcement the best way to reveal whether the fish wereclassifying the music on the basis of a categorical principle ratherthan on the basis of rote memory was to present novel stimuli There-fore scattered throughout the experiment were nine probe sessions in

which both the S+ and the S CDs were novel These were Sessions115 120 131 138 152 157 163 168 and 177 The music was se-lected for diversity within the genre S+ included four different per-formersrsquo CDs plus five compilation CDs with more than 20 addi-tional blues performers S consisted of six baroque-style CDs andthree non-baroque composersmdashspecifically Mozart Beethovenand Schubert

The buttonpressing response involves a fishrsquos entire body sincethe fish must position itself over the button and essentially ram itTherefore such a response is inherently somewhat slowmdashfar slowerthan for example a birdrsquos peck at a key or a ratrsquos press of a lever Be-cause the fish typically would not hover over the button and becausethey appeared to commit to a response by swimming in from a dis-tance after each S+ interval the silent ITI began with a grace periodof 1 sec during which a buttonpress would still be counted and re-inforced on the assumption that the response had begun during S+

During Sessions 147ndash149 the 200-Hz high-pass filter was turnedon in order to minimize stimulation of the lateral line The idea wasto try to ensure that the discrimination between blues and classicalwould be made on the basis of input from the fishrsquos inner ears thesensory system presumably most capable of detecting the f ine-grained acoustic features of music that form the basis for stylisticdistinctions by humans

The possibility of acoustic artifacts owing to hardware was testedby a control procedure in which the blues and the classical CDs wereeach loaded into the drive programmed for the other (Sessions 182ndash238) The effect was to reverse the definitions of S+ and S (ie toreinforce responses to classical music but not to blues) This was ex-pected to produce a dramatic decrement in accuracy which woulddemonstrate that responding had indeed been under the control ofthe musical content of the S+ and S channels

Results and DiscussionThe use of CRF imposed the obligation to verify that

the subjects were discriminating the stimuli and notmerely the current state of the multiple CRF-extinctionschedule Proof that a subject was not being cued by feed-back from routine test responses would be a statisticallysignificant difference between the percentages of S andS+ trials in which the subject did not press the button atall Such a finding would allow rejection of the hypothe-sis that the subject had been testing the button equally dur-ing both stimulus conditions The alternative hypothesis isdirectional in that beyond exhibiting a difference per sean auditorily discriminating subject would be expected toignore the response button more during S than during S+Therefore unless otherwise specified throughout thispaper significance is reported in terms of the p value of aone-tailed paired t test (Microsoft Excel 97 SR-1) on thenonresponse percentages associated with the two stimulustypes in each of n sessions the alpha level used was 05

As is indicated graphically in Figures 5 and 6 all 3 koidiscriminated blues from classical music and this behav-ior generalized into an ability to classify unfamiliar ex-emplars by genre [for each of the 3 subjects 9 probe ses-sions t(8) gt 10 p lt 001] To my knowledge this is thefirst demonstration in fish of open-ended categorization(Herrnstein 1992) and of any kind of categorization withauditory stimuli

Figure 5 shows the percentages of S+ and S trials inwhich there was no responding In Session 115 the firstprobe Beauty responded only during S+ and not at all dur-

MUSIC DISCRIMINATIONS BY CARP 341

ing S or ITI In Probe Session 138 the novel S was Vi-valdi guitar music which proved to raise problems Figure 6shows all the responses for each session note the higherS response rate at Session 138 Session 182 was the first

control-by-reversal session Sessions 138 and 182 are fur-ther discussed below

The data from the probe sessions are plotted in Figure 7and are shown in historical context in Figure 5 Figure 7

Figure 4 Experiments 1 and 2 (categorization and iterated reversals) stimulus chart Each column representsa single stimulus CD which is identified by text that starts in that column at the bottom of the figure Each rowrepresents a group of sessions Bullets indicate the CDs presented in their entirety as the S+ and S in each ses-sion group whereas the numbers associated with Sessions 56ndash100 identify the specific CD tracks used as stim-uli A triple bullet marks the first presentation of a given CD a single bullet denotes a stimulus heard previ-ously Rows in which both stimuli are represented by triple bullets denote groups of sessions in which the firstone exposed the subject to all-novel stimuli and thus served as a probe session

342 CHASE

also shows means for the nonprobe and the probe sessionsin the session range 115ndash181 The fish classified musicwith which they had had no training about as accurately asthey classified familiar training stimuli This generaliza-tion to unfamiliar exemplars demonstrates that the fishwere not relying on rote memory but were instead exhibit-ing open-ended categorization (Herrnstein 1992)

To assess whether the fish were exhibiting true percep-tion of categories preclusion of categorical perception(ie the inability to discriminate exemplars within a cat-egory) was necessary The great complexity of musicalstimuli renders likely the existence of a mix of feature di-mensions on the basis of which a sample only a few sec-onds long suffices to distinguish any two pieces or evendifferent performances of the same piece The blues stim-uli ranged from John Lee Hooker to Sonny Boy William-son and the classical ranged from baroque to Schubertboth categories featured a variety of ensembles It is im-plausible that recordings that sound so very different tohumans would be completely indistinguishable to thesefish The result of Experiment 4 below provides strongadditional evidence Koi can discriminate generically simi-lar melodies which implies that they can discriminategenerically similar recordings that differ along a multi-plicity of dimensions of which melody is only one

In Figures 5 and 6 the data for Sessions 182ndash192 showthe disruption of performance following the reversal of thereinforcement contingencies This reversal served as acontrol procedure the result of which confirmed that re-sponding was indeed under the control of the musical con-tent as opposed to any electronic artifact in the S+ andS audio channels

In Sessions 138ndash144 the fish had unexpected difficultydiscriminating Vivaldi guitar concertos from a blues com-pilation Although it is plausible that the fish could havelearned that guitar sounds were characteristic of blues theguitar concertos arguably did not sound to humans as muchlike blues as like the Vivaldi cello concerto which was theprevious S and which the fish had had no trouble dis-tinguishing from blues Another possible source of confu-sion for the f ish was the fact that this S+ was the firstcompilation CD to be presented as a stimulus Thus the di-versity of blues styles distinguished this S+ CD from anyprevious one Given the fishesrsquo problem with this dis-crimination I paired the Vivaldi guitar concertos with somevery familiar John Lee Hooker (Sessions 145ndash146) Whendiscrimination did not improve I left these stimuli in placebut turned on the 200-Hz high-pass filter for three ses-sions (147ndash149) As can be seen from Figure 5 the resultof turning on the filter was an immediate improvement inperformance which persisted after the filter was turnedoff Apparently these particular stimuli were salient andhad similar features in the lower frequencies which con-fused the fish until the high-pass filter forced them to at-tend to higher frequency features on the basis of whichthe music was more readily discriminable It would alsoappear that the lateral line was not necessary for the dis-crimination of familiar music As DrsquoAmato and Salmon

(1982) noted ldquoIndividuals do not always rely on the sameproperty of the stimulus and may according to circum-stances shift their reliance from one feature to anotherrdquo(p 130) (In any case Vivaldi evidently can impress listen-ers in odd ways Porter amp Neuringer 1984 reported thata Vivaldi violin concerto sounded more like Stravinsky thanlike Bach to their pigeons as it did also to some humans)

Even a convincing demonstration of categorization canfail to identify the stimulus features that exert control atany given time especially if the stimuli are complex In par-ticular there can be uncertainty as to whether classificationbehavior had been under the stimulus control of the fea-tures in terms of which the experimenter had defined thecategories or whether the subjects had discovered an ef-fective discriminant of which the experimenter was unawareThe diversity of S+S pairings (see Figure 4) presum-ably rules out the possibility that the fish could have beenrelying on only a single discriminant such as timbre buta constant concern is the possible existence of a simple at-tribute that would have allowed the subjects merely to dis-criminate instead of categorizing In the present experi-ment the choices of stimuli and control procedures wereintended to ensure that all the available discriminants weresufficiently complex For example even if a fish used asthe discriminant the sound of a human voice which waspresent in virtually all of the blues but in none of the clas-sical the diversity of singing voices would imply open-ended categorization nonetheless

The possibility that the fish memorized individual or re-curring features cannot be ruled out An animal probablydoes exploit a collection of memorized features alongwith various abstracted properties It would be surprisingif no features at all were salient enough to be rememberedand one wonders whether it is even possible to abstract acategorical discriminant without having particular fea-tures in memory at least temporarily

The notion that koi might classify blues and classicalmusic on the basis of deeper generic attributes is supportedby the results of experiments reported below which indi-cate that timbre cues are not required Porter and Neuringer(1984) trained pigeons to discriminate baroque from mod-ern music using initial exemplars that could have been al-ternatively classified as organ and orchestral music but theeffective discriminant turned out to be something otherthan instrumental timbre In a recent report (Watanabe ampSato 1999) Java sparrows learned to discriminate pianomusic by Schoumlnberg from piano music by Bach and theythen correctly classified orchestral music as Schoumlnberg-like or Bach-like whether written by those two composersor by Carter and (even) Vivaldi Studies that analyze the per-ceptual world of pigeons in terms of multidimensionalscaling spaces reveal that the birds learn enough aboutnonexemplars to form a distinct category for them as wellas for exemplars In other words pigeons appear to eval-uate a stimulus not only as possibly a good exemplar but alsoas a good nonexemplar which is more work than binaryclassification logically requires (Herrnstein 1994) Giventhat the more features of the environment to which one is

MUSIC DISCRIMINATIONS BY CARP 343

sensitive the more information is available from which todiscern patterns and changes indications that animalslearn more than the minimal solution to classificationproblems involving complex stimuli suggest that as com-pared with trying to ignore as much as possible of theworld evolution favors embracing its complexity

EXPERIMENT 2 Iterated Reversals

MethodThe first categorization session in which the contingencies were

reversed had served as a control procedure This experimental con-

0

25

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Tri

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Beauty

S-

S+

0

25

50

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100

Tri

als

wit

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Oro

S-

S+

200 Hz filter

0

25

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Tri

als

wit

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40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

Session Number

Pepi

S+

S-

S+ S- ITI

Figure 5 Experiment 1 (categorization) percentages of S+ (blues) and S (classical) trials and intertrial intervals (ITIs silence)during which the fish did not press the button at all plotted for each session The greater the separation between a sessionrsquos S+ andS nonresponse percentages the more clearly the subject was discriminating the stimuli as opposed to responding indiscriminatelyand receiving feedback from the reinforcement contingency The boxed data points indicate probe sessions The bar from Sessions147ndash149 shows where the 200-Hz low-frequency cutoff filter was used The circled data points (Session 182) indicate the first control-by-reversal session In the reversal sessions (182ndash192) S+ (still represented by open squares) was now classical music whereas S (stillrepresented by filled triangles) was blues Crosses denote silence

344 CHASE

dition (ie with blues now the S and classical now the S+) wasthen extended into an iterated-reversal experiment The primary goalwas to test koi in reversal learning with complex auditory stimuliafter having found nothing in the literature on the subject of auditoryreversal learning in fish

A secondary goal was to prepare for a planned experiment with aclassification procedure involving two visually distinct buttons withresponses on a particular button to be reinforced only in the presenceof a particular type of music The rim of the original button had beenmachined from black Delrin A new rim was made from an ivory-

colored blank of the same plastic and installed after six sessions ofthe unsignaled reversal (ie no change in the button) Thereafterrim color alternated in synchrony with contingency reversals withblack and ivory signaling that S+ was blues and classical respec-tively The fish would experience a total of four color changes thefirst of which did not signal a contingency change

The sessions were terminated by either the trial in which the 50thpellet was dispensed or an elapsed time of 90 min whichever camefirst Altogether there were 119 sessions spanning four reversals(see Figure 4)

Figure 6 Experiment 1 (categorization) all responses Number of responses in each session during blues trials classical trials andintertrial intervals (ITIs) Under the reversal condition that began with Session 182 blues became S and classical became S+ Bluesresponse counts above 50 reflect the onset of extinction Reversal sessions in which the classical response count was less than 50 wereterminated at 90 min Crosses denote silence

0

20

40

60

80

100

120

All

Pre

sses

40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

Session Number

Pepi

0

20

40

60

80

100

120

All

Pre

sses

ITI

Oro

0

20

40

60

80

100

120

All

Pre

sses

BeautyBluesClassicalITI

MUSIC DISCRIMINATIONS BY CARP 345

Just before the first reversal the stimuli had been a House of Bluescompilation (S+) and a baroque horn compilation (S ) When thecontingencies were reversed making blues S and classical S+both stimuli were also replaced The first reversal stimuli were Bachoboe concertos (S+) and John Lee Hookerrsquos Real Folks Blues (S )both very familiar to the fish In the next three phases of the first re-versal three additional pairs of familiar CDs were used In the fifthand final phase of the first reversal the fish were exposed to entirelynovel stimuli (S The Blues Story compilation S+ Bach triosonatas) As in the categorization study the first session with novelstimuli (Session 224) served as a probe testing for open-ended cat-egorization Blues and classical successively exchanged roles as S+and S in three additional reversal phases all using familiar stim-uli As can be seen in Figure 4 when the first and third reversals oc-curred at least one stimulus CD changed as well The final reversalbrought the contingencies back to where they had been before thefirst reversalmdashnamely with blues as S+ and classical as S

ResultsThe first reversal (Session 182) produced considerable

behavioral disruption and erroneous responding (see Fig-

ures 8 and 9) In the first 6ndash9 sessions the increase in re-sponding to the genre newly become S+ was insufficientfor any fish to earn 50 reinforcements within the 90-mintime limit (Figure 8) Beauty and Oro steadily improvedand were reliably discriminating by the 16th and 23rd ses-sions respectively Pepi achieved significance by Session 9but then his performance was substandard until Session 27[5 sessions ts(4) gt 229 p lt 010 p lt 009 and p lt 042respectively] Near the end of the first reversal the probesession (224) revealed that the classification behavior ex-hibited by Beauty and Oro was clearly open-ended catego-rization With each successive reversal it took fewer sessionsfor Beauty and Oro to demonstrate clear discrimination(Figures 9 and 10) Even Pepi eventually learned each re-versalmdashalbeit while continuing to call attention to the ex-istence of considerable and systematic individual differ-ences among fish In Figure 9 least-squares regressionlines are plotted for S nonresponse data and as is shownin Figure 10 their slopes indicate improvement rates of

0

50

100 Beauty

0

50

100 Oro

0

50

100

Mean 115 120 131 138 152 157 163 168 177 Mean

Probe Sessions (Novel CDs) Probes

Pepi

Non probes

S+S-ITI

Tri

als

wit

h N

o P

ress

Tri

als

wit

h N

o P

ress

Tri

als

wit

h N

o P

res

s

Figure 7 Experiment 1 (categorization) categorization performance during probe ses-sions (ie all-novel stimuli) percentages of S+ trials intertrial intervals (ITI) and S tri-als in which the fish did not respond Black bars indicate S+ gray bars indicate S andwhite bars indicate ITI Low nonresponse percentages for S+ indicate a high likelihoodof responding during S+ whereas high nonresponse percentages for S indicate that thefish tended to ignore the button during S The leftmost ldquoMeanrdquo bars show the averagesof all the nonprobe sessions in the session range 115ndash181 and the rightmost ldquoMeanrdquo barsshow the averages of the probe sessions

346 CHASE

08 and 11 per session for Beauty and Oro respec-tively during the first reversal (Sessions 182ndash238) Overthe final 5 sessions of each reversal phase discriminationby Beauty Oro and Pepi was statistically significant at

levels always better than p lt 010 p lt 016 and p lt 042respectively [ts(4) gt 229] It can be seen in Figure 8 thatwith each reversal the increase in responding to the new S+was generally faster than the extinction to the former S+

0

20

40

60

80

100

120

All

Pre

sses

Beauty

0

20

40

60

80

100

120

All

Pre

sses

Oro

ITI

Session Number

blues

classical classicalbluesblues

0

20

40

60

80

100

120

All

Pre

sses

150 175 200 225 250 275 300

Pepi

classical

BluesClassical

Figure 8 Experiment 2 (iterated reversals) counts of all responses by session Note that in graphs of reversal data the symbols con-sistently indicate genre (open squares blues filled triangles classical) not stimulus semantics (S+ or S ) which of course change ateach reversal This convention highlights the fluctuating response pattern associated with each genre longitudinally as successive re-versals of reinforcement contingency produce disruption and then learning with increasing efficiency The primary session termina-tion trigger was the trial on which the 50th pellet was delivered but in the early sessions of the first reversal no subject made as manyas 50 ldquocorrectrdquo responses to the former S within the session time limit even while responding many more than 50 times without re-inforcement to the former S+ Note that the extinction-induced response frenzy associated with a genrersquos suddenly becoming S de-creases with each reversal Crosses denote silence

MUSIC DISCRIMINATIONS BY CARP 347

EXPERIMENT 3Transition to Synthetic Keyboard Music and

Polyphonic Discrimination with Identical Timbre

The next step was to try to extend the learned classifi-cation of natural music to MIDI (Musical Instrument Dig-

ital Interface) synthesized music in which S+ and Swere not distinguishable by timbre

MethodPretraining After the iterated-reversal experiment the fish re-

mained in the homeexperimental tank from which all the appara-tus had been removed and they were not exposed to music or to anytraining or experimental procedures for a period of 10 months The

Tri

als

wit

h N

o P

ress

0

25

50

75

100

Reversals

Oro

classical

blues

classical

classical

blues

bluesTri

als

wit

h N

o P

ress

0

25

50

75

100

150 200 250 300

Session Number

Pepi

0

25

50

75

100

First Reversal

Beauty

Probe

Tri

als

wit

h N

o P

ress

ITI

BluesClassicalITI

Figure 9 Experiment 2 (iterated reversals) percentages of trials with no responses by session Note the increasingly efficient learn-ing of nonresponding to each former S+ as shown by the increasing slopes of the least-squares regression lines Session 224 (dashedline) was a probe the accurate discrimination of entirely novel stimuli indicates that the fish were performing open-ended catego-rization Crosses denote silence

348 CHASE

work resumed with a reintroduction to the apparatus and protocol asleft off at the end of the fourth and final reversalmdashthat is with S+and S being blues and classical respectively However the fishwere also being prepared to encounter the synthetic stimuli that werebeing created at that time which consisted of a single short piecefrom each genre rather than a collection comparable in duration andvariety with the commercial CDs used previously Therefore in pre-training the stimuli were the same two CDs the subjects had lastheard (see Figure 4 Session 300) but only a single track from eachS was an excerpt from a Bach oboe concerto S+ was the John LeeHooker song ldquoOne Bourbon One Scotch and One Beerrdquo of whicha synthesized version was in the works

Initially Beauty and Oro seemed to manifest effects of the longhiatus in the form of low response rates (not enough to earn 50 pel-lets in a session) and some transient difficulties operating the buttonand taking pellets from the nipple However even allowing for somerelearning and the reduced size of the new stimuli the immediacywith which all 3 subjects exhibited highly accurate discriminationsuggests that the original discrimination training had been retained(compare the leftmost sessions in Figure 11 with the rightmost inFigure 9)

Procedure The new stimuli were musically simplif ied MIDIkeyboard renditions of music of the types the f ish had alreadylearned to classify S+ was the familiar blues song described aboveand S was the unfamiliar Fugue 2 from Book I of Bachrsquos Well-Tempered Clavier To minimize the presence of extraneous cues allthe performances were done by the same musician with the sameequipment (a Kurzweil Model k2000vp keyboard Young Chang Re-search and Development Institute Waltham MA) the same se-quencing software (Studio Vision Pro Version 40 Opcode SystemsNashville TN) and the same settings for volume and for timbre(acoustic piano) Because the new stimuli were so short that theywould repeat after only a few trials rote memory could play a rolein their discrimination and thus the operative level of stimulus con-trol was being allowed to potentially regress from categorization todiscrimination

The initial synthetic stimuli turned out to trigger a deteriorationin classification accuracy (Figure 11 Session 13) It seemed possi-ble that this was an artifact of the musical translation process be-cause even humans had some difficulty recognizing the John LeeHooker song in synthetic form It had gone from bluesy to bouncyits original bass inflections were absent and there was no melodicvoice comparable with that of the singer Therefore at Session 24 Iintroduced a second generation of stimuli S+ remained the samepiece but the performance was somewhat more faithful to themodel The old S (the Bach fugue) had been much shorter than S+and thus had been repeating more often so it was replaced by a syn-

thesized rendition of the f irst movement of Vivaldirsquos ConcertoGrosso in A minor Opus 3 No 6 whose duration more closelymatched that of S+ In addition the timbre of the blues was changedfrom acoustic piano to rock piano thus adding timbre as an availablediscriminant However from Session 47 until the end of the experi-ment S+ and S again had timbre in common specifically rockpiano (starting in Session 47) chiffloot (starting in Session 55) andguitar (starting in Session 62)

ResultsWith the first presentations in a synthetic timbre discrim-

ination accuracy deteriorated (Figure 11 Sessions 13ndash23)perhaps because the first synthetic S+ was not a good enoughexemplar of the blues genre Pepi essentially ceased re-sponding during this time and had to be dropped from thestudy Starting at Session 24 with improved stimuli and adifference in timbre between S+ and S the behavior ofboth remaining subjects immediately changed and there-after their discriminative accuracy improved continually

When S+ and S were again made identical in timbre(Session 47) accurate classification persisted despite aperformance decrement probably related to the loss of asalient cue When the same pair of MIDI sequences waspresented in additional timbres generalization of accurateclassification to the new sounds appeared seamless The datafrom Session 47 and onward demonstrate [Sessions 18ts(17) gt 16 ps lt 001] that koi are capable of discriminat-ing polyphonic music on the basis of features other thanthe timbre of individual tone sources

EXPERIMENT 4 Discrimination of Melodies

Without Timbre Cues

After observing that instrumental timbre seemed not tobe a necessary discriminant in polyphonic music I inves-tigated whether timbre was necessary for koi to discrimi-nate single-voice musicmdashthat is melodies

MethodIn order to familiarize the subjects with the S+ melody and also

in hopes of rehabilitating Pepi this experiment began with severalsessions of collective exposure to a sound-versus-silence contin-gency CRF signaled by the music that would later be the S+ in thesound-versus-sound discrimination alternated with extinction sig-naled by silence In this group pretraining Pepi was observed bothpressing the button and taking pellets from the nipple but when sub-sequently isolated for melody discrimination sessions he consis-tently shied away from the nipple and again had to be dropped as asubject

The stimuli for the melody discrimination experiment (Figure 12)were all derived from the theme from Paganinirsquos 24th Caprice forsolo violin which is perhaps best known from Rachmaninoff rsquosldquoRhapsody on a Theme by Paganinirdquo S+ was the original melody asperformed on the MIDI keyboard S was derived from S+ by usingthe transformation described by Poli and Previde (1991) By using acomputer to modify the MIDI score S+rsquos order of pitches was re-versed whereas its original order of note durations was retained Inother words the first note of S got the duration of S+rsquos first notebut the pitch of S+rsquos last note the second note of S got the durationof S+rsquos second note but the pitch of S+rsquos next-to-last note and so onThis procedure can be thought of as retaining the rhythm track while

0

1

2

3S

lop

e (

ch

ang

ese

ssio

n)

1 2 3 4

Reversal Number

OroBeauty

Pepi

Figure 10 Experiment 2 (iterated reversals) improvementtrends For Beauty and Oro the improvement rate (Figure 9 re-gression line slopes percentage of nonresponse S trials per ses-sion) increases with each reversal

MUSIC DISCRIMINATIONS BY CARP 349

reversing the pitch track The result is two stimuli that are ldquoidenticalwith respect to their mean frequency note duration and rhythm butnoticeably different in their melodic patternsrdquo (Poli amp Previde 1991p 12) Such a pitch-track-reversed melody differs from a completelybackwards melody only in rhythm sacrificing the linkage betweeneach pitch and its original duration in order to preserve the originalsequence of durations per se (If the original melodymdashunlike the

Rachmaninoffmdashhas a palindromic rhythm track the pitch-track -reversed melody and the completely backwards melody are identical)The melodies were recorded using the same MIDI apparatus as thatdescribed above To enhance clarity the tempo was somewhat slowerthan that of the usual piano performance

Over the course of 53 sessions the instrumental timbre alternatedsix times between strings and acoustic piano but in any given ses-

0

25

50

75

100

Tri

als

wit

h N

o P

res

s

S+

ITI

S-

Beauty

0

25

50

75

100

Tri

als

wit

h N

o P

ress

S+

ITI

S-

Oro

Same Timbre Different Timbre Same Timbre

S+S-ITI

Pepi ceased responding

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 Session Number

S+

ITI

S-

Pepi

Figure 11 Experiment 3 (transition to MIDI and timbre study) percentages of S+ and S trials dur-ing which the fish did not press the button During the first 12 sessions the stimuli consisted of a singletrack from each of the two commercial recordings the subjects had last heard 10 months earlier at theconclusion of the iterated-reversal experiment the immediate resumption of accurate discrimination sug-gests long-term memory of training The circled data points (Sessions 13 and 24) indicate the introduc-tion of the first- and second-generation synthetic music From Session 47 until the end of the experimentS+ and S had identical timbre each boxed data point pair indicates the first presentation of a new tim-bre Session 47 rock piano Session 55 chiffloot and Session 62 guitar Crosses denote silence

350 CHASE

sion S+ and S always had the same timbre The discrimination pro-tocol was unchanged from the previous experiments except that thesession termination trigger was raised from 50 to 55 pellets As a pre-liminary test for a possible perceptual invariance (Hulse Takeuchi ampBraaten 1992) S+ was transposed down a fifth in Sessions 51ndash52

After 53 sessions it was discovered that the MIDI technology hadintroduced artifactual differences between S+ and S A musicallyattuned visitor to the lab detected minor variations in note durationsbetween the two stimuli which apparently had resulted from incor-rect handling of the attackndashsustainndashdecay envelopes of S+rsquos recordednotes There also turned out to be subtle volume differences whichwere said to have resulted from the combination of the MIDI scoreediting process and the volume compression function in the digitalaudio tape (DAT) recorder used to create stimulus master tapesThese differences were confirmed by careful examination of thewaveforms using a computer oscilloscope Therefore a second gen-eration of S was created by direct numerical substitution of the S+pitches into the MIDI score in reverse order and by recording a newmaster tape with all volume compression disabled The correctionswere verified by waveform analysis

After eight sessions with the second-generat ion S both S+ andS were shortened by the removal of each onersquos distinctive initial noteand seven sessions later they were further shortened by the removal oftheir remaining initial six and final four notes The purpose of thesestimulus contractions was to look for behavioral disruption that might

indicate that the subject had been discriminating the melodies on thebasis of such local features as the absolute pitch of the initial note

Results and DiscussionBeautyrsquos performance inexplicably deteriorated to the

point where he had to be dropped as a subjectFigures 13 and 14 report the performance of Oro the only

fish to complete the melody experiment The data showthat without timbre cues Oro clearly discriminated betweenthe two melodies [in each stimulus condition (ie second-generation S first-note-removed and both-ends-clipped)5 final sessions t(4) gt 10 p lt 001]

Oro responded more to S+ than to S even in the veryfirst session with melodic stimuli Familiarization with theS+ during pretraining could well have contributed to thisresponse bias perhaps partly because music heard in asound-versus-silence context had consistently become theS+ in a subsequent sound-versus-sound discriminationHowever the MIDI artifacts in the first-generation stim-uli might also have played a role

Session 54 in which the corrected S was introducedmarks a significant reduction of the separation between

Figure 12 Experiment 4 (melody discrimination) musical scores of the normal (S+) and pitch-reversed (S )melodies

MUSIC DISCRIMINATIONS BY CARP 351

the S+ and the S nonresponse percentages [two-tailed two-sample t test assuming unequal variances contrasting themean difference between S and S+ nonresponse per-centages before and after the change 8 observations just be-fore the stimulus change vs 8 observations just after t(11) =277 p lt 019] This implies that the rather subtle artifactsin the original S had indeed been exploited as discrimi-nants

One oddity is the fact that although the stimuli changedsignificantly in Sessions 54 (second-generation S ) and62 (removal of the first note of S+ and S ) in each case

a pronounced anomaly in Ororsquos performance occurred inthe following session

Studies of melody discrimination in animals have oftenfound that the behavior was controlled by local featuressuch as timbre pitch register or the absolute pitch of the ini-tial note rather than by the melodic patterning per se(DrsquoAmato amp Salmon 1984 Hulse amp Cynx 1985 Hulseamp Page 1988 Poli amp Previde 1991) (In this paper for theterm local properties I follow the convention of referringnot only to features like distinctive individual notes whichare clearly local in a temporal sense but also to features

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 70

Session Number

S+

S-

= Piano= Down a fifth= wo 1st note= wo 1st 7 amp last 4 notes

S+S-ITI

Figure 13 Experiment 4 (melody discrimination) trials with no responses The MIDI timbre was violin except for 13 sessions ofpiano as marked The corrected S was introduced at Session 54 The first notes of S+ and S were removed at Session 62 The sixinitial and four final notes were removed at Session 69 Crosses denote silence

Figure 14 Experiment 4 (melody discrimination) all responses Sessions terminated with the S+ trial in which the 55th pel-let was dispensed Crosses denote silence

0

20

40

60

All

Pre

sses

0 10 20 30 40 50 60 70

Session Number

S+

S-

Oro

S+S-ITI

352 CHASE

like timbre and pitch register which although recogniz-able in any local segment can be constant over the dura-tion of the stimulus and which therefore might arguablybe called global properties) It should not be surprisingthat with sequential stimuli such as sound animals oftenexploit local features in preference to global pattern fea-tures In the acoustic domain features that are instantly rec-ognizable presumably confer a survival advantage not onlyon listeners but also on creatures in whose interest it is tobe identifiable by sounds they make Oro did not have tim-bre available as a discriminant but there is no conclusiveevidence that he did or did not use other local features andit is not known which if any global features he might haveused

It warrants mention that in this type of discriminationexperiment inaccurate responding need not imply that thesubject is musically insensitive because musical sensitiv-ity can actually confound discriminative accuracy if bothstimuli are musically plausible or stylistically similar In-deed throughout this experiment the stimuli were moni-tored through a speaker in the laboratory office and S+ andS became so familiar and the pitch-track-reversed Ssounded so pleasing that human observers occasionallybecame confused as to which reinforcement contingencywas in force in the tank

The finding that Oro did not need timbre cues to dis-criminate melodies contrasts sharply with the result in ratsreported by Poli and Previde (1991) Using as stimuli for-ward and pitch-track-reversed versions of the melodyldquoFregravere Jacquesrdquo they tested for discrimination on the basisof melodic pattern The rats had neither previous experi-mental experience nor prior familiarity with music In anattempt to preclude the exploitation of local features suchas the absolute pitch of distinctively positioned notes each15-sec stimulus presentation began at a randomly chosenposition within the melody Different groups of subjectswere asked to discriminate two melodic stimuli that dif-fered in melody only in timbre only or in both attributesHowever the stimuli were never heard as unitary melodiesfrom start to finish and were presented in a continuousstream of randomly sequenced exposures with responsesin the presence of S+ being reinforced only on an FR-5schedule This would seem to be such a formidable task asto make it unsurprising that animals failed except when tim-bre a consistent property of every note in each stimuluswas available as a discriminant However Poli and Previdedid suggest that rats might well prove able to discriminatemelodies without timbre cues under other conditions

CONCLUDING REMARKS

The distinction between local features and pattern fea-tures although it arose in connection with melody dis-crimination is equally relevant to the categorization ex-periment To say that in classifying music as blues orclassical the koi might have been responding to deepgeneric attributes is not to say that they were necessarilyusing anything other than local cues because the diag-

nostic property could have been a particular combinationof timbre loudness pitch brief rhythmic or melodic fig-ures and other such local features A human scanning aradio dial requires only a fraction of a second to identifythe genre of a given station hardly enough time for patternfeatures to manifest themselves so a brief sample of musiccould well contain something recognizable to an animalthat had a rote store of auditory feature memories Localfeatures might control classification behavior even whenthere is extensive exposure to a stimulus Conceivably an-imals could acquire a functional understanding of musicentirely on the basis of the distribution and frequency ofvarious combinations of essentially local features with-out regard to the artistic pattern features in terms of whichmusical genres are commonly defined

Prior to this series of experiments the prevailing opinionappeared to be skepticism as to whether koi could dis-criminate one piece of music from another under any cir-cumstances Now it appears that these animals can discrim-inate polyphonic music discriminate melodic patternsand even classify music by artistic genre As far as I knowthese experiments presented the most complex auditorystimuli to which fish have ever been shown capable ofmaking sophisticated discriminative responses Howeverthere remains the task of elucidating the stimulus controlfunctions of the constituents of that complexity such aspattern features local features and simple properties of thestimulus as a whole The present work was intended as ex-ploratory rather than explanatory and the results clearly ex-tend the known envelope of auditory capabilities in fish

REFERENCES

Baron M R (1965) The stimulus stimulus control and generaliza-tion In D I Mostovsky (Ed) Stimulus generalization (pp 62-71)Stanford CA Stanford University Press

Chase A R amp Hill W (1999) Reliable operant apparatus for fishAudio stimulus generator response button and pellet-dispensing nip-ple Behavior Research Methods Instruments amp Computers 31 470-478

Coombs S Jannsen J amp Montgomery J C (1992) Functional andevolutionary implications of peripheral diversity in lateral line sys-tems In D B Webster R R Fay amp A N Popper (Eds) The evolu-tionary biology of hearing (pp 267-294) New York Springer-Verlag

DrsquoAmato M R amp Salmon D P (1982) Tune discrimination in mon-keys (Cebus apella) and rats Animal Learning amp Behavior 10 126-134

DrsquoAmato M R amp Salmon D P (1984) Processing of complex au-ditory stimuli (tunes) by rats and monkeys (Cebus apella) AnimalLearning amp Behavior 12 184-194

Fay R R (1988) Hearing in vertebrates A psychophysics data-bookWinnetka IL Hill-Fay Associates

Fay R R (1992) Analytic listening in goldfish Hearing Research 59101-107

Fay R R (1994) Perception of temporal acoustic patterns by the gold-fish (Carassius auratus) Hearing Research 76 158-172

Fay R R (1995) Perception of spectrally and temporally complexsounds by the goldfish (Carassius auratus) Hearing Research 89146-154

Fay R R (1998) Auditory stream segregation in goldfish (Carassiusauratus) Hearing Research 120 69-76

Fay R R amp Ream T J (1986) Acoustic response and tuning in sac-cular nerve fibers of the goldfish (Carassius auratus) Journal of theAcoustical Society of America 79 1883-1895

Hartman W M (1988) Pitch perception and the segregation and inte-

MUSIC DISCRIMINATIONS BY CARP 341

ing S or ITI In Probe Session 138 the novel S was Vi-valdi guitar music which proved to raise problems Figure 6shows all the responses for each session note the higherS response rate at Session 138 Session 182 was the first

control-by-reversal session Sessions 138 and 182 are fur-ther discussed below

The data from the probe sessions are plotted in Figure 7and are shown in historical context in Figure 5 Figure 7

Figure 4 Experiments 1 and 2 (categorization and iterated reversals) stimulus chart Each column representsa single stimulus CD which is identified by text that starts in that column at the bottom of the figure Each rowrepresents a group of sessions Bullets indicate the CDs presented in their entirety as the S+ and S in each ses-sion group whereas the numbers associated with Sessions 56ndash100 identify the specific CD tracks used as stim-uli A triple bullet marks the first presentation of a given CD a single bullet denotes a stimulus heard previ-ously Rows in which both stimuli are represented by triple bullets denote groups of sessions in which the firstone exposed the subject to all-novel stimuli and thus served as a probe session

342 CHASE

also shows means for the nonprobe and the probe sessionsin the session range 115ndash181 The fish classified musicwith which they had had no training about as accurately asthey classified familiar training stimuli This generaliza-tion to unfamiliar exemplars demonstrates that the fishwere not relying on rote memory but were instead exhibit-ing open-ended categorization (Herrnstein 1992)

To assess whether the fish were exhibiting true percep-tion of categories preclusion of categorical perception(ie the inability to discriminate exemplars within a cat-egory) was necessary The great complexity of musicalstimuli renders likely the existence of a mix of feature di-mensions on the basis of which a sample only a few sec-onds long suffices to distinguish any two pieces or evendifferent performances of the same piece The blues stim-uli ranged from John Lee Hooker to Sonny Boy William-son and the classical ranged from baroque to Schubertboth categories featured a variety of ensembles It is im-plausible that recordings that sound so very different tohumans would be completely indistinguishable to thesefish The result of Experiment 4 below provides strongadditional evidence Koi can discriminate generically simi-lar melodies which implies that they can discriminategenerically similar recordings that differ along a multi-plicity of dimensions of which melody is only one

In Figures 5 and 6 the data for Sessions 182ndash192 showthe disruption of performance following the reversal of thereinforcement contingencies This reversal served as acontrol procedure the result of which confirmed that re-sponding was indeed under the control of the musical con-tent as opposed to any electronic artifact in the S+ andS audio channels

In Sessions 138ndash144 the fish had unexpected difficultydiscriminating Vivaldi guitar concertos from a blues com-pilation Although it is plausible that the fish could havelearned that guitar sounds were characteristic of blues theguitar concertos arguably did not sound to humans as muchlike blues as like the Vivaldi cello concerto which was theprevious S and which the fish had had no trouble dis-tinguishing from blues Another possible source of confu-sion for the f ish was the fact that this S+ was the firstcompilation CD to be presented as a stimulus Thus the di-versity of blues styles distinguished this S+ CD from anyprevious one Given the fishesrsquo problem with this dis-crimination I paired the Vivaldi guitar concertos with somevery familiar John Lee Hooker (Sessions 145ndash146) Whendiscrimination did not improve I left these stimuli in placebut turned on the 200-Hz high-pass filter for three ses-sions (147ndash149) As can be seen from Figure 5 the resultof turning on the filter was an immediate improvement inperformance which persisted after the filter was turnedoff Apparently these particular stimuli were salient andhad similar features in the lower frequencies which con-fused the fish until the high-pass filter forced them to at-tend to higher frequency features on the basis of whichthe music was more readily discriminable It would alsoappear that the lateral line was not necessary for the dis-crimination of familiar music As DrsquoAmato and Salmon

(1982) noted ldquoIndividuals do not always rely on the sameproperty of the stimulus and may according to circum-stances shift their reliance from one feature to anotherrdquo(p 130) (In any case Vivaldi evidently can impress listen-ers in odd ways Porter amp Neuringer 1984 reported thata Vivaldi violin concerto sounded more like Stravinsky thanlike Bach to their pigeons as it did also to some humans)

Even a convincing demonstration of categorization canfail to identify the stimulus features that exert control atany given time especially if the stimuli are complex In par-ticular there can be uncertainty as to whether classificationbehavior had been under the stimulus control of the fea-tures in terms of which the experimenter had defined thecategories or whether the subjects had discovered an ef-fective discriminant of which the experimenter was unawareThe diversity of S+S pairings (see Figure 4) presum-ably rules out the possibility that the fish could have beenrelying on only a single discriminant such as timbre buta constant concern is the possible existence of a simple at-tribute that would have allowed the subjects merely to dis-criminate instead of categorizing In the present experi-ment the choices of stimuli and control procedures wereintended to ensure that all the available discriminants weresufficiently complex For example even if a fish used asthe discriminant the sound of a human voice which waspresent in virtually all of the blues but in none of the clas-sical the diversity of singing voices would imply open-ended categorization nonetheless

The possibility that the fish memorized individual or re-curring features cannot be ruled out An animal probablydoes exploit a collection of memorized features alongwith various abstracted properties It would be surprisingif no features at all were salient enough to be rememberedand one wonders whether it is even possible to abstract acategorical discriminant without having particular fea-tures in memory at least temporarily

The notion that koi might classify blues and classicalmusic on the basis of deeper generic attributes is supportedby the results of experiments reported below which indi-cate that timbre cues are not required Porter and Neuringer(1984) trained pigeons to discriminate baroque from mod-ern music using initial exemplars that could have been al-ternatively classified as organ and orchestral music but theeffective discriminant turned out to be something otherthan instrumental timbre In a recent report (Watanabe ampSato 1999) Java sparrows learned to discriminate pianomusic by Schoumlnberg from piano music by Bach and theythen correctly classified orchestral music as Schoumlnberg-like or Bach-like whether written by those two composersor by Carter and (even) Vivaldi Studies that analyze the per-ceptual world of pigeons in terms of multidimensionalscaling spaces reveal that the birds learn enough aboutnonexemplars to form a distinct category for them as wellas for exemplars In other words pigeons appear to eval-uate a stimulus not only as possibly a good exemplar but alsoas a good nonexemplar which is more work than binaryclassification logically requires (Herrnstein 1994) Giventhat the more features of the environment to which one is

MUSIC DISCRIMINATIONS BY CARP 343

sensitive the more information is available from which todiscern patterns and changes indications that animalslearn more than the minimal solution to classificationproblems involving complex stimuli suggest that as com-pared with trying to ignore as much as possible of theworld evolution favors embracing its complexity

EXPERIMENT 2 Iterated Reversals

MethodThe first categorization session in which the contingencies were

reversed had served as a control procedure This experimental con-

0

25

50

75

100

Tri

als

wit

h N

o P

ress

Beauty

S-

S+

0

25

50

75

100

Tri

als

wit

h N

o P

ress

Oro

S-

S+

200 Hz filter

0

25

50

75

100

Tri

als

wit

h N

o P

ress

40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

Session Number

Pepi

S+

S-

S+ S- ITI

Figure 5 Experiment 1 (categorization) percentages of S+ (blues) and S (classical) trials and intertrial intervals (ITIs silence)during which the fish did not press the button at all plotted for each session The greater the separation between a sessionrsquos S+ andS nonresponse percentages the more clearly the subject was discriminating the stimuli as opposed to responding indiscriminatelyand receiving feedback from the reinforcement contingency The boxed data points indicate probe sessions The bar from Sessions147ndash149 shows where the 200-Hz low-frequency cutoff filter was used The circled data points (Session 182) indicate the first control-by-reversal session In the reversal sessions (182ndash192) S+ (still represented by open squares) was now classical music whereas S (stillrepresented by filled triangles) was blues Crosses denote silence

344 CHASE

dition (ie with blues now the S and classical now the S+) wasthen extended into an iterated-reversal experiment The primary goalwas to test koi in reversal learning with complex auditory stimuliafter having found nothing in the literature on the subject of auditoryreversal learning in fish

A secondary goal was to prepare for a planned experiment with aclassification procedure involving two visually distinct buttons withresponses on a particular button to be reinforced only in the presenceof a particular type of music The rim of the original button had beenmachined from black Delrin A new rim was made from an ivory-

colored blank of the same plastic and installed after six sessions ofthe unsignaled reversal (ie no change in the button) Thereafterrim color alternated in synchrony with contingency reversals withblack and ivory signaling that S+ was blues and classical respec-tively The fish would experience a total of four color changes thefirst of which did not signal a contingency change

The sessions were terminated by either the trial in which the 50thpellet was dispensed or an elapsed time of 90 min whichever camefirst Altogether there were 119 sessions spanning four reversals(see Figure 4)

Figure 6 Experiment 1 (categorization) all responses Number of responses in each session during blues trials classical trials andintertrial intervals (ITIs) Under the reversal condition that began with Session 182 blues became S and classical became S+ Bluesresponse counts above 50 reflect the onset of extinction Reversal sessions in which the classical response count was less than 50 wereterminated at 90 min Crosses denote silence

0

20

40

60

80

100

120

All

Pre

sses

40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

Session Number

Pepi

0

20

40

60

80

100

120

All

Pre

sses

ITI

Oro

0

20

40

60

80

100

120

All

Pre

sses

BeautyBluesClassicalITI

MUSIC DISCRIMINATIONS BY CARP 345

Just before the first reversal the stimuli had been a House of Bluescompilation (S+) and a baroque horn compilation (S ) When thecontingencies were reversed making blues S and classical S+both stimuli were also replaced The first reversal stimuli were Bachoboe concertos (S+) and John Lee Hookerrsquos Real Folks Blues (S )both very familiar to the fish In the next three phases of the first re-versal three additional pairs of familiar CDs were used In the fifthand final phase of the first reversal the fish were exposed to entirelynovel stimuli (S The Blues Story compilation S+ Bach triosonatas) As in the categorization study the first session with novelstimuli (Session 224) served as a probe testing for open-ended cat-egorization Blues and classical successively exchanged roles as S+and S in three additional reversal phases all using familiar stim-uli As can be seen in Figure 4 when the first and third reversals oc-curred at least one stimulus CD changed as well The final reversalbrought the contingencies back to where they had been before thefirst reversalmdashnamely with blues as S+ and classical as S

ResultsThe first reversal (Session 182) produced considerable

behavioral disruption and erroneous responding (see Fig-

ures 8 and 9) In the first 6ndash9 sessions the increase in re-sponding to the genre newly become S+ was insufficientfor any fish to earn 50 reinforcements within the 90-mintime limit (Figure 8) Beauty and Oro steadily improvedand were reliably discriminating by the 16th and 23rd ses-sions respectively Pepi achieved significance by Session 9but then his performance was substandard until Session 27[5 sessions ts(4) gt 229 p lt 010 p lt 009 and p lt 042respectively] Near the end of the first reversal the probesession (224) revealed that the classification behavior ex-hibited by Beauty and Oro was clearly open-ended catego-rization With each successive reversal it took fewer sessionsfor Beauty and Oro to demonstrate clear discrimination(Figures 9 and 10) Even Pepi eventually learned each re-versalmdashalbeit while continuing to call attention to the ex-istence of considerable and systematic individual differ-ences among fish In Figure 9 least-squares regressionlines are plotted for S nonresponse data and as is shownin Figure 10 their slopes indicate improvement rates of

0

50

100 Beauty

0

50

100 Oro

0

50

100

Mean 115 120 131 138 152 157 163 168 177 Mean

Probe Sessions (Novel CDs) Probes

Pepi

Non probes

S+S-ITI

Tri

als

wit

h N

o P

ress

Tri

als

wit

h N

o P

ress

Tri

als

wit

h N

o P

res

s

Figure 7 Experiment 1 (categorization) categorization performance during probe ses-sions (ie all-novel stimuli) percentages of S+ trials intertrial intervals (ITI) and S tri-als in which the fish did not respond Black bars indicate S+ gray bars indicate S andwhite bars indicate ITI Low nonresponse percentages for S+ indicate a high likelihoodof responding during S+ whereas high nonresponse percentages for S indicate that thefish tended to ignore the button during S The leftmost ldquoMeanrdquo bars show the averagesof all the nonprobe sessions in the session range 115ndash181 and the rightmost ldquoMeanrdquo barsshow the averages of the probe sessions

346 CHASE

08 and 11 per session for Beauty and Oro respec-tively during the first reversal (Sessions 182ndash238) Overthe final 5 sessions of each reversal phase discriminationby Beauty Oro and Pepi was statistically significant at

levels always better than p lt 010 p lt 016 and p lt 042respectively [ts(4) gt 229] It can be seen in Figure 8 thatwith each reversal the increase in responding to the new S+was generally faster than the extinction to the former S+

0

20

40

60

80

100

120

All

Pre

sses

Beauty

0

20

40

60

80

100

120

All

Pre

sses

Oro

ITI

Session Number

blues

classical classicalbluesblues

0

20

40

60

80

100

120

All

Pre

sses

150 175 200 225 250 275 300

Pepi

classical

BluesClassical

Figure 8 Experiment 2 (iterated reversals) counts of all responses by session Note that in graphs of reversal data the symbols con-sistently indicate genre (open squares blues filled triangles classical) not stimulus semantics (S+ or S ) which of course change ateach reversal This convention highlights the fluctuating response pattern associated with each genre longitudinally as successive re-versals of reinforcement contingency produce disruption and then learning with increasing efficiency The primary session termina-tion trigger was the trial on which the 50th pellet was delivered but in the early sessions of the first reversal no subject made as manyas 50 ldquocorrectrdquo responses to the former S within the session time limit even while responding many more than 50 times without re-inforcement to the former S+ Note that the extinction-induced response frenzy associated with a genrersquos suddenly becoming S de-creases with each reversal Crosses denote silence

MUSIC DISCRIMINATIONS BY CARP 347

EXPERIMENT 3Transition to Synthetic Keyboard Music and

Polyphonic Discrimination with Identical Timbre

The next step was to try to extend the learned classifi-cation of natural music to MIDI (Musical Instrument Dig-

ital Interface) synthesized music in which S+ and Swere not distinguishable by timbre

MethodPretraining After the iterated-reversal experiment the fish re-

mained in the homeexperimental tank from which all the appara-tus had been removed and they were not exposed to music or to anytraining or experimental procedures for a period of 10 months The

Tri

als

wit

h N

o P

ress

0

25

50

75

100

Reversals

Oro

classical

blues

classical

classical

blues

bluesTri

als

wit

h N

o P

ress

0

25

50

75

100

150 200 250 300

Session Number

Pepi

0

25

50

75

100

First Reversal

Beauty

Probe

Tri

als

wit

h N

o P

ress

ITI

BluesClassicalITI

Figure 9 Experiment 2 (iterated reversals) percentages of trials with no responses by session Note the increasingly efficient learn-ing of nonresponding to each former S+ as shown by the increasing slopes of the least-squares regression lines Session 224 (dashedline) was a probe the accurate discrimination of entirely novel stimuli indicates that the fish were performing open-ended catego-rization Crosses denote silence

348 CHASE

work resumed with a reintroduction to the apparatus and protocol asleft off at the end of the fourth and final reversalmdashthat is with S+and S being blues and classical respectively However the fishwere also being prepared to encounter the synthetic stimuli that werebeing created at that time which consisted of a single short piecefrom each genre rather than a collection comparable in duration andvariety with the commercial CDs used previously Therefore in pre-training the stimuli were the same two CDs the subjects had lastheard (see Figure 4 Session 300) but only a single track from eachS was an excerpt from a Bach oboe concerto S+ was the John LeeHooker song ldquoOne Bourbon One Scotch and One Beerrdquo of whicha synthesized version was in the works

Initially Beauty and Oro seemed to manifest effects of the longhiatus in the form of low response rates (not enough to earn 50 pel-lets in a session) and some transient difficulties operating the buttonand taking pellets from the nipple However even allowing for somerelearning and the reduced size of the new stimuli the immediacywith which all 3 subjects exhibited highly accurate discriminationsuggests that the original discrimination training had been retained(compare the leftmost sessions in Figure 11 with the rightmost inFigure 9)

Procedure The new stimuli were musically simplif ied MIDIkeyboard renditions of music of the types the f ish had alreadylearned to classify S+ was the familiar blues song described aboveand S was the unfamiliar Fugue 2 from Book I of Bachrsquos Well-Tempered Clavier To minimize the presence of extraneous cues allthe performances were done by the same musician with the sameequipment (a Kurzweil Model k2000vp keyboard Young Chang Re-search and Development Institute Waltham MA) the same se-quencing software (Studio Vision Pro Version 40 Opcode SystemsNashville TN) and the same settings for volume and for timbre(acoustic piano) Because the new stimuli were so short that theywould repeat after only a few trials rote memory could play a rolein their discrimination and thus the operative level of stimulus con-trol was being allowed to potentially regress from categorization todiscrimination

The initial synthetic stimuli turned out to trigger a deteriorationin classification accuracy (Figure 11 Session 13) It seemed possi-ble that this was an artifact of the musical translation process be-cause even humans had some difficulty recognizing the John LeeHooker song in synthetic form It had gone from bluesy to bouncyits original bass inflections were absent and there was no melodicvoice comparable with that of the singer Therefore at Session 24 Iintroduced a second generation of stimuli S+ remained the samepiece but the performance was somewhat more faithful to themodel The old S (the Bach fugue) had been much shorter than S+and thus had been repeating more often so it was replaced by a syn-

thesized rendition of the f irst movement of Vivaldirsquos ConcertoGrosso in A minor Opus 3 No 6 whose duration more closelymatched that of S+ In addition the timbre of the blues was changedfrom acoustic piano to rock piano thus adding timbre as an availablediscriminant However from Session 47 until the end of the experi-ment S+ and S again had timbre in common specifically rockpiano (starting in Session 47) chiffloot (starting in Session 55) andguitar (starting in Session 62)

ResultsWith the first presentations in a synthetic timbre discrim-

ination accuracy deteriorated (Figure 11 Sessions 13ndash23)perhaps because the first synthetic S+ was not a good enoughexemplar of the blues genre Pepi essentially ceased re-sponding during this time and had to be dropped from thestudy Starting at Session 24 with improved stimuli and adifference in timbre between S+ and S the behavior ofboth remaining subjects immediately changed and there-after their discriminative accuracy improved continually

When S+ and S were again made identical in timbre(Session 47) accurate classification persisted despite aperformance decrement probably related to the loss of asalient cue When the same pair of MIDI sequences waspresented in additional timbres generalization of accurateclassification to the new sounds appeared seamless The datafrom Session 47 and onward demonstrate [Sessions 18ts(17) gt 16 ps lt 001] that koi are capable of discriminat-ing polyphonic music on the basis of features other thanthe timbre of individual tone sources

EXPERIMENT 4 Discrimination of Melodies

Without Timbre Cues

After observing that instrumental timbre seemed not tobe a necessary discriminant in polyphonic music I inves-tigated whether timbre was necessary for koi to discrimi-nate single-voice musicmdashthat is melodies

MethodIn order to familiarize the subjects with the S+ melody and also

in hopes of rehabilitating Pepi this experiment began with severalsessions of collective exposure to a sound-versus-silence contin-gency CRF signaled by the music that would later be the S+ in thesound-versus-sound discrimination alternated with extinction sig-naled by silence In this group pretraining Pepi was observed bothpressing the button and taking pellets from the nipple but when sub-sequently isolated for melody discrimination sessions he consis-tently shied away from the nipple and again had to be dropped as asubject

The stimuli for the melody discrimination experiment (Figure 12)were all derived from the theme from Paganinirsquos 24th Caprice forsolo violin which is perhaps best known from Rachmaninoff rsquosldquoRhapsody on a Theme by Paganinirdquo S+ was the original melody asperformed on the MIDI keyboard S was derived from S+ by usingthe transformation described by Poli and Previde (1991) By using acomputer to modify the MIDI score S+rsquos order of pitches was re-versed whereas its original order of note durations was retained Inother words the first note of S got the duration of S+rsquos first notebut the pitch of S+rsquos last note the second note of S got the durationof S+rsquos second note but the pitch of S+rsquos next-to-last note and so onThis procedure can be thought of as retaining the rhythm track while

0

1

2

3S

lop

e (

ch

ang

ese

ssio

n)

1 2 3 4

Reversal Number

OroBeauty

Pepi

Figure 10 Experiment 2 (iterated reversals) improvementtrends For Beauty and Oro the improvement rate (Figure 9 re-gression line slopes percentage of nonresponse S trials per ses-sion) increases with each reversal

MUSIC DISCRIMINATIONS BY CARP 349

reversing the pitch track The result is two stimuli that are ldquoidenticalwith respect to their mean frequency note duration and rhythm butnoticeably different in their melodic patternsrdquo (Poli amp Previde 1991p 12) Such a pitch-track-reversed melody differs from a completelybackwards melody only in rhythm sacrificing the linkage betweeneach pitch and its original duration in order to preserve the originalsequence of durations per se (If the original melodymdashunlike the

Rachmaninoffmdashhas a palindromic rhythm track the pitch-track -reversed melody and the completely backwards melody are identical)The melodies were recorded using the same MIDI apparatus as thatdescribed above To enhance clarity the tempo was somewhat slowerthan that of the usual piano performance

Over the course of 53 sessions the instrumental timbre alternatedsix times between strings and acoustic piano but in any given ses-

0

25

50

75

100

Tri

als

wit

h N

o P

res

s

S+

ITI

S-

Beauty

0

25

50

75

100

Tri

als

wit

h N

o P

ress

S+

ITI

S-

Oro

Same Timbre Different Timbre Same Timbre

S+S-ITI

Pepi ceased responding

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 Session Number

S+

ITI

S-

Pepi

Figure 11 Experiment 3 (transition to MIDI and timbre study) percentages of S+ and S trials dur-ing which the fish did not press the button During the first 12 sessions the stimuli consisted of a singletrack from each of the two commercial recordings the subjects had last heard 10 months earlier at theconclusion of the iterated-reversal experiment the immediate resumption of accurate discrimination sug-gests long-term memory of training The circled data points (Sessions 13 and 24) indicate the introduc-tion of the first- and second-generation synthetic music From Session 47 until the end of the experimentS+ and S had identical timbre each boxed data point pair indicates the first presentation of a new tim-bre Session 47 rock piano Session 55 chiffloot and Session 62 guitar Crosses denote silence

350 CHASE

sion S+ and S always had the same timbre The discrimination pro-tocol was unchanged from the previous experiments except that thesession termination trigger was raised from 50 to 55 pellets As a pre-liminary test for a possible perceptual invariance (Hulse Takeuchi ampBraaten 1992) S+ was transposed down a fifth in Sessions 51ndash52

After 53 sessions it was discovered that the MIDI technology hadintroduced artifactual differences between S+ and S A musicallyattuned visitor to the lab detected minor variations in note durationsbetween the two stimuli which apparently had resulted from incor-rect handling of the attackndashsustainndashdecay envelopes of S+rsquos recordednotes There also turned out to be subtle volume differences whichwere said to have resulted from the combination of the MIDI scoreediting process and the volume compression function in the digitalaudio tape (DAT) recorder used to create stimulus master tapesThese differences were confirmed by careful examination of thewaveforms using a computer oscilloscope Therefore a second gen-eration of S was created by direct numerical substitution of the S+pitches into the MIDI score in reverse order and by recording a newmaster tape with all volume compression disabled The correctionswere verified by waveform analysis

After eight sessions with the second-generat ion S both S+ andS were shortened by the removal of each onersquos distinctive initial noteand seven sessions later they were further shortened by the removal oftheir remaining initial six and final four notes The purpose of thesestimulus contractions was to look for behavioral disruption that might

indicate that the subject had been discriminating the melodies on thebasis of such local features as the absolute pitch of the initial note

Results and DiscussionBeautyrsquos performance inexplicably deteriorated to the

point where he had to be dropped as a subjectFigures 13 and 14 report the performance of Oro the only

fish to complete the melody experiment The data showthat without timbre cues Oro clearly discriminated betweenthe two melodies [in each stimulus condition (ie second-generation S first-note-removed and both-ends-clipped)5 final sessions t(4) gt 10 p lt 001]

Oro responded more to S+ than to S even in the veryfirst session with melodic stimuli Familiarization with theS+ during pretraining could well have contributed to thisresponse bias perhaps partly because music heard in asound-versus-silence context had consistently become theS+ in a subsequent sound-versus-sound discriminationHowever the MIDI artifacts in the first-generation stim-uli might also have played a role

Session 54 in which the corrected S was introducedmarks a significant reduction of the separation between

Figure 12 Experiment 4 (melody discrimination) musical scores of the normal (S+) and pitch-reversed (S )melodies

MUSIC DISCRIMINATIONS BY CARP 351

the S+ and the S nonresponse percentages [two-tailed two-sample t test assuming unequal variances contrasting themean difference between S and S+ nonresponse per-centages before and after the change 8 observations just be-fore the stimulus change vs 8 observations just after t(11) =277 p lt 019] This implies that the rather subtle artifactsin the original S had indeed been exploited as discrimi-nants

One oddity is the fact that although the stimuli changedsignificantly in Sessions 54 (second-generation S ) and62 (removal of the first note of S+ and S ) in each case

a pronounced anomaly in Ororsquos performance occurred inthe following session

Studies of melody discrimination in animals have oftenfound that the behavior was controlled by local featuressuch as timbre pitch register or the absolute pitch of the ini-tial note rather than by the melodic patterning per se(DrsquoAmato amp Salmon 1984 Hulse amp Cynx 1985 Hulseamp Page 1988 Poli amp Previde 1991) (In this paper for theterm local properties I follow the convention of referringnot only to features like distinctive individual notes whichare clearly local in a temporal sense but also to features

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 70

Session Number

S+

S-

= Piano= Down a fifth= wo 1st note= wo 1st 7 amp last 4 notes

S+S-ITI

Figure 13 Experiment 4 (melody discrimination) trials with no responses The MIDI timbre was violin except for 13 sessions ofpiano as marked The corrected S was introduced at Session 54 The first notes of S+ and S were removed at Session 62 The sixinitial and four final notes were removed at Session 69 Crosses denote silence

Figure 14 Experiment 4 (melody discrimination) all responses Sessions terminated with the S+ trial in which the 55th pel-let was dispensed Crosses denote silence

0

20

40

60

All

Pre

sses

0 10 20 30 40 50 60 70

Session Number

S+

S-

Oro

S+S-ITI

352 CHASE

like timbre and pitch register which although recogniz-able in any local segment can be constant over the dura-tion of the stimulus and which therefore might arguablybe called global properties) It should not be surprisingthat with sequential stimuli such as sound animals oftenexploit local features in preference to global pattern fea-tures In the acoustic domain features that are instantly rec-ognizable presumably confer a survival advantage not onlyon listeners but also on creatures in whose interest it is tobe identifiable by sounds they make Oro did not have tim-bre available as a discriminant but there is no conclusiveevidence that he did or did not use other local features andit is not known which if any global features he might haveused

It warrants mention that in this type of discriminationexperiment inaccurate responding need not imply that thesubject is musically insensitive because musical sensitiv-ity can actually confound discriminative accuracy if bothstimuli are musically plausible or stylistically similar In-deed throughout this experiment the stimuli were moni-tored through a speaker in the laboratory office and S+ andS became so familiar and the pitch-track-reversed Ssounded so pleasing that human observers occasionallybecame confused as to which reinforcement contingencywas in force in the tank

The finding that Oro did not need timbre cues to dis-criminate melodies contrasts sharply with the result in ratsreported by Poli and Previde (1991) Using as stimuli for-ward and pitch-track-reversed versions of the melodyldquoFregravere Jacquesrdquo they tested for discrimination on the basisof melodic pattern The rats had neither previous experi-mental experience nor prior familiarity with music In anattempt to preclude the exploitation of local features suchas the absolute pitch of distinctively positioned notes each15-sec stimulus presentation began at a randomly chosenposition within the melody Different groups of subjectswere asked to discriminate two melodic stimuli that dif-fered in melody only in timbre only or in both attributesHowever the stimuli were never heard as unitary melodiesfrom start to finish and were presented in a continuousstream of randomly sequenced exposures with responsesin the presence of S+ being reinforced only on an FR-5schedule This would seem to be such a formidable task asto make it unsurprising that animals failed except when tim-bre a consistent property of every note in each stimuluswas available as a discriminant However Poli and Previdedid suggest that rats might well prove able to discriminatemelodies without timbre cues under other conditions

CONCLUDING REMARKS

The distinction between local features and pattern fea-tures although it arose in connection with melody dis-crimination is equally relevant to the categorization ex-periment To say that in classifying music as blues orclassical the koi might have been responding to deepgeneric attributes is not to say that they were necessarilyusing anything other than local cues because the diag-

nostic property could have been a particular combinationof timbre loudness pitch brief rhythmic or melodic fig-ures and other such local features A human scanning aradio dial requires only a fraction of a second to identifythe genre of a given station hardly enough time for patternfeatures to manifest themselves so a brief sample of musiccould well contain something recognizable to an animalthat had a rote store of auditory feature memories Localfeatures might control classification behavior even whenthere is extensive exposure to a stimulus Conceivably an-imals could acquire a functional understanding of musicentirely on the basis of the distribution and frequency ofvarious combinations of essentially local features with-out regard to the artistic pattern features in terms of whichmusical genres are commonly defined

Prior to this series of experiments the prevailing opinionappeared to be skepticism as to whether koi could dis-criminate one piece of music from another under any cir-cumstances Now it appears that these animals can discrim-inate polyphonic music discriminate melodic patternsand even classify music by artistic genre As far as I knowthese experiments presented the most complex auditorystimuli to which fish have ever been shown capable ofmaking sophisticated discriminative responses Howeverthere remains the task of elucidating the stimulus controlfunctions of the constituents of that complexity such aspattern features local features and simple properties of thestimulus as a whole The present work was intended as ex-ploratory rather than explanatory and the results clearly ex-tend the known envelope of auditory capabilities in fish

REFERENCES

Baron M R (1965) The stimulus stimulus control and generaliza-tion In D I Mostovsky (Ed) Stimulus generalization (pp 62-71)Stanford CA Stanford University Press

Chase A R amp Hill W (1999) Reliable operant apparatus for fishAudio stimulus generator response button and pellet-dispensing nip-ple Behavior Research Methods Instruments amp Computers 31 470-478

Coombs S Jannsen J amp Montgomery J C (1992) Functional andevolutionary implications of peripheral diversity in lateral line sys-tems In D B Webster R R Fay amp A N Popper (Eds) The evolu-tionary biology of hearing (pp 267-294) New York Springer-Verlag

DrsquoAmato M R amp Salmon D P (1982) Tune discrimination in mon-keys (Cebus apella) and rats Animal Learning amp Behavior 10 126-134

DrsquoAmato M R amp Salmon D P (1984) Processing of complex au-ditory stimuli (tunes) by rats and monkeys (Cebus apella) AnimalLearning amp Behavior 12 184-194

Fay R R (1988) Hearing in vertebrates A psychophysics data-bookWinnetka IL Hill-Fay Associates

Fay R R (1992) Analytic listening in goldfish Hearing Research 59101-107

Fay R R (1994) Perception of temporal acoustic patterns by the gold-fish (Carassius auratus) Hearing Research 76 158-172

Fay R R (1995) Perception of spectrally and temporally complexsounds by the goldfish (Carassius auratus) Hearing Research 89146-154

Fay R R (1998) Auditory stream segregation in goldfish (Carassiusauratus) Hearing Research 120 69-76

Fay R R amp Ream T J (1986) Acoustic response and tuning in sac-cular nerve fibers of the goldfish (Carassius auratus) Journal of theAcoustical Society of America 79 1883-1895

Hartman W M (1988) Pitch perception and the segregation and inte-

342 CHASE

also shows means for the nonprobe and the probe sessionsin the session range 115ndash181 The fish classified musicwith which they had had no training about as accurately asthey classified familiar training stimuli This generaliza-tion to unfamiliar exemplars demonstrates that the fishwere not relying on rote memory but were instead exhibit-ing open-ended categorization (Herrnstein 1992)

To assess whether the fish were exhibiting true percep-tion of categories preclusion of categorical perception(ie the inability to discriminate exemplars within a cat-egory) was necessary The great complexity of musicalstimuli renders likely the existence of a mix of feature di-mensions on the basis of which a sample only a few sec-onds long suffices to distinguish any two pieces or evendifferent performances of the same piece The blues stim-uli ranged from John Lee Hooker to Sonny Boy William-son and the classical ranged from baroque to Schubertboth categories featured a variety of ensembles It is im-plausible that recordings that sound so very different tohumans would be completely indistinguishable to thesefish The result of Experiment 4 below provides strongadditional evidence Koi can discriminate generically simi-lar melodies which implies that they can discriminategenerically similar recordings that differ along a multi-plicity of dimensions of which melody is only one

In Figures 5 and 6 the data for Sessions 182ndash192 showthe disruption of performance following the reversal of thereinforcement contingencies This reversal served as acontrol procedure the result of which confirmed that re-sponding was indeed under the control of the musical con-tent as opposed to any electronic artifact in the S+ andS audio channels

In Sessions 138ndash144 the fish had unexpected difficultydiscriminating Vivaldi guitar concertos from a blues com-pilation Although it is plausible that the fish could havelearned that guitar sounds were characteristic of blues theguitar concertos arguably did not sound to humans as muchlike blues as like the Vivaldi cello concerto which was theprevious S and which the fish had had no trouble dis-tinguishing from blues Another possible source of confu-sion for the f ish was the fact that this S+ was the firstcompilation CD to be presented as a stimulus Thus the di-versity of blues styles distinguished this S+ CD from anyprevious one Given the fishesrsquo problem with this dis-crimination I paired the Vivaldi guitar concertos with somevery familiar John Lee Hooker (Sessions 145ndash146) Whendiscrimination did not improve I left these stimuli in placebut turned on the 200-Hz high-pass filter for three ses-sions (147ndash149) As can be seen from Figure 5 the resultof turning on the filter was an immediate improvement inperformance which persisted after the filter was turnedoff Apparently these particular stimuli were salient andhad similar features in the lower frequencies which con-fused the fish until the high-pass filter forced them to at-tend to higher frequency features on the basis of whichthe music was more readily discriminable It would alsoappear that the lateral line was not necessary for the dis-crimination of familiar music As DrsquoAmato and Salmon

(1982) noted ldquoIndividuals do not always rely on the sameproperty of the stimulus and may according to circum-stances shift their reliance from one feature to anotherrdquo(p 130) (In any case Vivaldi evidently can impress listen-ers in odd ways Porter amp Neuringer 1984 reported thata Vivaldi violin concerto sounded more like Stravinsky thanlike Bach to their pigeons as it did also to some humans)

Even a convincing demonstration of categorization canfail to identify the stimulus features that exert control atany given time especially if the stimuli are complex In par-ticular there can be uncertainty as to whether classificationbehavior had been under the stimulus control of the fea-tures in terms of which the experimenter had defined thecategories or whether the subjects had discovered an ef-fective discriminant of which the experimenter was unawareThe diversity of S+S pairings (see Figure 4) presum-ably rules out the possibility that the fish could have beenrelying on only a single discriminant such as timbre buta constant concern is the possible existence of a simple at-tribute that would have allowed the subjects merely to dis-criminate instead of categorizing In the present experi-ment the choices of stimuli and control procedures wereintended to ensure that all the available discriminants weresufficiently complex For example even if a fish used asthe discriminant the sound of a human voice which waspresent in virtually all of the blues but in none of the clas-sical the diversity of singing voices would imply open-ended categorization nonetheless

The possibility that the fish memorized individual or re-curring features cannot be ruled out An animal probablydoes exploit a collection of memorized features alongwith various abstracted properties It would be surprisingif no features at all were salient enough to be rememberedand one wonders whether it is even possible to abstract acategorical discriminant without having particular fea-tures in memory at least temporarily

The notion that koi might classify blues and classicalmusic on the basis of deeper generic attributes is supportedby the results of experiments reported below which indi-cate that timbre cues are not required Porter and Neuringer(1984) trained pigeons to discriminate baroque from mod-ern music using initial exemplars that could have been al-ternatively classified as organ and orchestral music but theeffective discriminant turned out to be something otherthan instrumental timbre In a recent report (Watanabe ampSato 1999) Java sparrows learned to discriminate pianomusic by Schoumlnberg from piano music by Bach and theythen correctly classified orchestral music as Schoumlnberg-like or Bach-like whether written by those two composersor by Carter and (even) Vivaldi Studies that analyze the per-ceptual world of pigeons in terms of multidimensionalscaling spaces reveal that the birds learn enough aboutnonexemplars to form a distinct category for them as wellas for exemplars In other words pigeons appear to eval-uate a stimulus not only as possibly a good exemplar but alsoas a good nonexemplar which is more work than binaryclassification logically requires (Herrnstein 1994) Giventhat the more features of the environment to which one is

MUSIC DISCRIMINATIONS BY CARP 343

sensitive the more information is available from which todiscern patterns and changes indications that animalslearn more than the minimal solution to classificationproblems involving complex stimuli suggest that as com-pared with trying to ignore as much as possible of theworld evolution favors embracing its complexity

EXPERIMENT 2 Iterated Reversals

MethodThe first categorization session in which the contingencies were

reversed had served as a control procedure This experimental con-

0

25

50

75

100

Tri

als

wit

h N

o P

ress

Beauty

S-

S+

0

25

50

75

100

Tri

als

wit

h N

o P

ress

Oro

S-

S+

200 Hz filter

0

25

50

75

100

Tri

als

wit

h N

o P

ress

40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

Session Number

Pepi

S+

S-

S+ S- ITI

Figure 5 Experiment 1 (categorization) percentages of S+ (blues) and S (classical) trials and intertrial intervals (ITIs silence)during which the fish did not press the button at all plotted for each session The greater the separation between a sessionrsquos S+ andS nonresponse percentages the more clearly the subject was discriminating the stimuli as opposed to responding indiscriminatelyand receiving feedback from the reinforcement contingency The boxed data points indicate probe sessions The bar from Sessions147ndash149 shows where the 200-Hz low-frequency cutoff filter was used The circled data points (Session 182) indicate the first control-by-reversal session In the reversal sessions (182ndash192) S+ (still represented by open squares) was now classical music whereas S (stillrepresented by filled triangles) was blues Crosses denote silence

344 CHASE

dition (ie with blues now the S and classical now the S+) wasthen extended into an iterated-reversal experiment The primary goalwas to test koi in reversal learning with complex auditory stimuliafter having found nothing in the literature on the subject of auditoryreversal learning in fish

A secondary goal was to prepare for a planned experiment with aclassification procedure involving two visually distinct buttons withresponses on a particular button to be reinforced only in the presenceof a particular type of music The rim of the original button had beenmachined from black Delrin A new rim was made from an ivory-

colored blank of the same plastic and installed after six sessions ofthe unsignaled reversal (ie no change in the button) Thereafterrim color alternated in synchrony with contingency reversals withblack and ivory signaling that S+ was blues and classical respec-tively The fish would experience a total of four color changes thefirst of which did not signal a contingency change

The sessions were terminated by either the trial in which the 50thpellet was dispensed or an elapsed time of 90 min whichever camefirst Altogether there were 119 sessions spanning four reversals(see Figure 4)

Figure 6 Experiment 1 (categorization) all responses Number of responses in each session during blues trials classical trials andintertrial intervals (ITIs) Under the reversal condition that began with Session 182 blues became S and classical became S+ Bluesresponse counts above 50 reflect the onset of extinction Reversal sessions in which the classical response count was less than 50 wereterminated at 90 min Crosses denote silence

0

20

40

60

80

100

120

All

Pre

sses

40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

Session Number

Pepi

0

20

40

60

80

100

120

All

Pre

sses

ITI

Oro

0

20

40

60

80

100

120

All

Pre

sses

BeautyBluesClassicalITI

MUSIC DISCRIMINATIONS BY CARP 345

Just before the first reversal the stimuli had been a House of Bluescompilation (S+) and a baroque horn compilation (S ) When thecontingencies were reversed making blues S and classical S+both stimuli were also replaced The first reversal stimuli were Bachoboe concertos (S+) and John Lee Hookerrsquos Real Folks Blues (S )both very familiar to the fish In the next three phases of the first re-versal three additional pairs of familiar CDs were used In the fifthand final phase of the first reversal the fish were exposed to entirelynovel stimuli (S The Blues Story compilation S+ Bach triosonatas) As in the categorization study the first session with novelstimuli (Session 224) served as a probe testing for open-ended cat-egorization Blues and classical successively exchanged roles as S+and S in three additional reversal phases all using familiar stim-uli As can be seen in Figure 4 when the first and third reversals oc-curred at least one stimulus CD changed as well The final reversalbrought the contingencies back to where they had been before thefirst reversalmdashnamely with blues as S+ and classical as S

ResultsThe first reversal (Session 182) produced considerable

behavioral disruption and erroneous responding (see Fig-

ures 8 and 9) In the first 6ndash9 sessions the increase in re-sponding to the genre newly become S+ was insufficientfor any fish to earn 50 reinforcements within the 90-mintime limit (Figure 8) Beauty and Oro steadily improvedand were reliably discriminating by the 16th and 23rd ses-sions respectively Pepi achieved significance by Session 9but then his performance was substandard until Session 27[5 sessions ts(4) gt 229 p lt 010 p lt 009 and p lt 042respectively] Near the end of the first reversal the probesession (224) revealed that the classification behavior ex-hibited by Beauty and Oro was clearly open-ended catego-rization With each successive reversal it took fewer sessionsfor Beauty and Oro to demonstrate clear discrimination(Figures 9 and 10) Even Pepi eventually learned each re-versalmdashalbeit while continuing to call attention to the ex-istence of considerable and systematic individual differ-ences among fish In Figure 9 least-squares regressionlines are plotted for S nonresponse data and as is shownin Figure 10 their slopes indicate improvement rates of

0

50

100 Beauty

0

50

100 Oro

0

50

100

Mean 115 120 131 138 152 157 163 168 177 Mean

Probe Sessions (Novel CDs) Probes

Pepi

Non probes

S+S-ITI

Tri

als

wit

h N

o P

ress

Tri

als

wit

h N

o P

ress

Tri

als

wit

h N

o P

res

s

Figure 7 Experiment 1 (categorization) categorization performance during probe ses-sions (ie all-novel stimuli) percentages of S+ trials intertrial intervals (ITI) and S tri-als in which the fish did not respond Black bars indicate S+ gray bars indicate S andwhite bars indicate ITI Low nonresponse percentages for S+ indicate a high likelihoodof responding during S+ whereas high nonresponse percentages for S indicate that thefish tended to ignore the button during S The leftmost ldquoMeanrdquo bars show the averagesof all the nonprobe sessions in the session range 115ndash181 and the rightmost ldquoMeanrdquo barsshow the averages of the probe sessions

346 CHASE

08 and 11 per session for Beauty and Oro respec-tively during the first reversal (Sessions 182ndash238) Overthe final 5 sessions of each reversal phase discriminationby Beauty Oro and Pepi was statistically significant at

levels always better than p lt 010 p lt 016 and p lt 042respectively [ts(4) gt 229] It can be seen in Figure 8 thatwith each reversal the increase in responding to the new S+was generally faster than the extinction to the former S+

0

20

40

60

80

100

120

All

Pre

sses

Beauty

0

20

40

60

80

100

120

All

Pre

sses

Oro

ITI

Session Number

blues

classical classicalbluesblues

0

20

40

60

80

100

120

All

Pre

sses

150 175 200 225 250 275 300

Pepi

classical

BluesClassical

Figure 8 Experiment 2 (iterated reversals) counts of all responses by session Note that in graphs of reversal data the symbols con-sistently indicate genre (open squares blues filled triangles classical) not stimulus semantics (S+ or S ) which of course change ateach reversal This convention highlights the fluctuating response pattern associated with each genre longitudinally as successive re-versals of reinforcement contingency produce disruption and then learning with increasing efficiency The primary session termina-tion trigger was the trial on which the 50th pellet was delivered but in the early sessions of the first reversal no subject made as manyas 50 ldquocorrectrdquo responses to the former S within the session time limit even while responding many more than 50 times without re-inforcement to the former S+ Note that the extinction-induced response frenzy associated with a genrersquos suddenly becoming S de-creases with each reversal Crosses denote silence

MUSIC DISCRIMINATIONS BY CARP 347

EXPERIMENT 3Transition to Synthetic Keyboard Music and

Polyphonic Discrimination with Identical Timbre

The next step was to try to extend the learned classifi-cation of natural music to MIDI (Musical Instrument Dig-

ital Interface) synthesized music in which S+ and Swere not distinguishable by timbre

MethodPretraining After the iterated-reversal experiment the fish re-

mained in the homeexperimental tank from which all the appara-tus had been removed and they were not exposed to music or to anytraining or experimental procedures for a period of 10 months The

Tri

als

wit

h N

o P

ress

0

25

50

75

100

Reversals

Oro

classical

blues

classical

classical

blues

bluesTri

als

wit

h N

o P

ress

0

25

50

75

100

150 200 250 300

Session Number

Pepi

0

25

50

75

100

First Reversal

Beauty

Probe

Tri

als

wit

h N

o P

ress

ITI

BluesClassicalITI

Figure 9 Experiment 2 (iterated reversals) percentages of trials with no responses by session Note the increasingly efficient learn-ing of nonresponding to each former S+ as shown by the increasing slopes of the least-squares regression lines Session 224 (dashedline) was a probe the accurate discrimination of entirely novel stimuli indicates that the fish were performing open-ended catego-rization Crosses denote silence

348 CHASE

work resumed with a reintroduction to the apparatus and protocol asleft off at the end of the fourth and final reversalmdashthat is with S+and S being blues and classical respectively However the fishwere also being prepared to encounter the synthetic stimuli that werebeing created at that time which consisted of a single short piecefrom each genre rather than a collection comparable in duration andvariety with the commercial CDs used previously Therefore in pre-training the stimuli were the same two CDs the subjects had lastheard (see Figure 4 Session 300) but only a single track from eachS was an excerpt from a Bach oboe concerto S+ was the John LeeHooker song ldquoOne Bourbon One Scotch and One Beerrdquo of whicha synthesized version was in the works

Initially Beauty and Oro seemed to manifest effects of the longhiatus in the form of low response rates (not enough to earn 50 pel-lets in a session) and some transient difficulties operating the buttonand taking pellets from the nipple However even allowing for somerelearning and the reduced size of the new stimuli the immediacywith which all 3 subjects exhibited highly accurate discriminationsuggests that the original discrimination training had been retained(compare the leftmost sessions in Figure 11 with the rightmost inFigure 9)

Procedure The new stimuli were musically simplif ied MIDIkeyboard renditions of music of the types the f ish had alreadylearned to classify S+ was the familiar blues song described aboveand S was the unfamiliar Fugue 2 from Book I of Bachrsquos Well-Tempered Clavier To minimize the presence of extraneous cues allthe performances were done by the same musician with the sameequipment (a Kurzweil Model k2000vp keyboard Young Chang Re-search and Development Institute Waltham MA) the same se-quencing software (Studio Vision Pro Version 40 Opcode SystemsNashville TN) and the same settings for volume and for timbre(acoustic piano) Because the new stimuli were so short that theywould repeat after only a few trials rote memory could play a rolein their discrimination and thus the operative level of stimulus con-trol was being allowed to potentially regress from categorization todiscrimination

The initial synthetic stimuli turned out to trigger a deteriorationin classification accuracy (Figure 11 Session 13) It seemed possi-ble that this was an artifact of the musical translation process be-cause even humans had some difficulty recognizing the John LeeHooker song in synthetic form It had gone from bluesy to bouncyits original bass inflections were absent and there was no melodicvoice comparable with that of the singer Therefore at Session 24 Iintroduced a second generation of stimuli S+ remained the samepiece but the performance was somewhat more faithful to themodel The old S (the Bach fugue) had been much shorter than S+and thus had been repeating more often so it was replaced by a syn-

thesized rendition of the f irst movement of Vivaldirsquos ConcertoGrosso in A minor Opus 3 No 6 whose duration more closelymatched that of S+ In addition the timbre of the blues was changedfrom acoustic piano to rock piano thus adding timbre as an availablediscriminant However from Session 47 until the end of the experi-ment S+ and S again had timbre in common specifically rockpiano (starting in Session 47) chiffloot (starting in Session 55) andguitar (starting in Session 62)

ResultsWith the first presentations in a synthetic timbre discrim-

ination accuracy deteriorated (Figure 11 Sessions 13ndash23)perhaps because the first synthetic S+ was not a good enoughexemplar of the blues genre Pepi essentially ceased re-sponding during this time and had to be dropped from thestudy Starting at Session 24 with improved stimuli and adifference in timbre between S+ and S the behavior ofboth remaining subjects immediately changed and there-after their discriminative accuracy improved continually

When S+ and S were again made identical in timbre(Session 47) accurate classification persisted despite aperformance decrement probably related to the loss of asalient cue When the same pair of MIDI sequences waspresented in additional timbres generalization of accurateclassification to the new sounds appeared seamless The datafrom Session 47 and onward demonstrate [Sessions 18ts(17) gt 16 ps lt 001] that koi are capable of discriminat-ing polyphonic music on the basis of features other thanthe timbre of individual tone sources

EXPERIMENT 4 Discrimination of Melodies

Without Timbre Cues

After observing that instrumental timbre seemed not tobe a necessary discriminant in polyphonic music I inves-tigated whether timbre was necessary for koi to discrimi-nate single-voice musicmdashthat is melodies

MethodIn order to familiarize the subjects with the S+ melody and also

in hopes of rehabilitating Pepi this experiment began with severalsessions of collective exposure to a sound-versus-silence contin-gency CRF signaled by the music that would later be the S+ in thesound-versus-sound discrimination alternated with extinction sig-naled by silence In this group pretraining Pepi was observed bothpressing the button and taking pellets from the nipple but when sub-sequently isolated for melody discrimination sessions he consis-tently shied away from the nipple and again had to be dropped as asubject

The stimuli for the melody discrimination experiment (Figure 12)were all derived from the theme from Paganinirsquos 24th Caprice forsolo violin which is perhaps best known from Rachmaninoff rsquosldquoRhapsody on a Theme by Paganinirdquo S+ was the original melody asperformed on the MIDI keyboard S was derived from S+ by usingthe transformation described by Poli and Previde (1991) By using acomputer to modify the MIDI score S+rsquos order of pitches was re-versed whereas its original order of note durations was retained Inother words the first note of S got the duration of S+rsquos first notebut the pitch of S+rsquos last note the second note of S got the durationof S+rsquos second note but the pitch of S+rsquos next-to-last note and so onThis procedure can be thought of as retaining the rhythm track while

0

1

2

3S

lop

e (

ch

ang

ese

ssio

n)

1 2 3 4

Reversal Number

OroBeauty

Pepi

Figure 10 Experiment 2 (iterated reversals) improvementtrends For Beauty and Oro the improvement rate (Figure 9 re-gression line slopes percentage of nonresponse S trials per ses-sion) increases with each reversal

MUSIC DISCRIMINATIONS BY CARP 349

reversing the pitch track The result is two stimuli that are ldquoidenticalwith respect to their mean frequency note duration and rhythm butnoticeably different in their melodic patternsrdquo (Poli amp Previde 1991p 12) Such a pitch-track-reversed melody differs from a completelybackwards melody only in rhythm sacrificing the linkage betweeneach pitch and its original duration in order to preserve the originalsequence of durations per se (If the original melodymdashunlike the

Rachmaninoffmdashhas a palindromic rhythm track the pitch-track -reversed melody and the completely backwards melody are identical)The melodies were recorded using the same MIDI apparatus as thatdescribed above To enhance clarity the tempo was somewhat slowerthan that of the usual piano performance

Over the course of 53 sessions the instrumental timbre alternatedsix times between strings and acoustic piano but in any given ses-

0

25

50

75

100

Tri

als

wit

h N

o P

res

s

S+

ITI

S-

Beauty

0

25

50

75

100

Tri

als

wit

h N

o P

ress

S+

ITI

S-

Oro

Same Timbre Different Timbre Same Timbre

S+S-ITI

Pepi ceased responding

0

25

50

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100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 Session Number

S+

ITI

S-

Pepi

Figure 11 Experiment 3 (transition to MIDI and timbre study) percentages of S+ and S trials dur-ing which the fish did not press the button During the first 12 sessions the stimuli consisted of a singletrack from each of the two commercial recordings the subjects had last heard 10 months earlier at theconclusion of the iterated-reversal experiment the immediate resumption of accurate discrimination sug-gests long-term memory of training The circled data points (Sessions 13 and 24) indicate the introduc-tion of the first- and second-generation synthetic music From Session 47 until the end of the experimentS+ and S had identical timbre each boxed data point pair indicates the first presentation of a new tim-bre Session 47 rock piano Session 55 chiffloot and Session 62 guitar Crosses denote silence

350 CHASE

sion S+ and S always had the same timbre The discrimination pro-tocol was unchanged from the previous experiments except that thesession termination trigger was raised from 50 to 55 pellets As a pre-liminary test for a possible perceptual invariance (Hulse Takeuchi ampBraaten 1992) S+ was transposed down a fifth in Sessions 51ndash52

After 53 sessions it was discovered that the MIDI technology hadintroduced artifactual differences between S+ and S A musicallyattuned visitor to the lab detected minor variations in note durationsbetween the two stimuli which apparently had resulted from incor-rect handling of the attackndashsustainndashdecay envelopes of S+rsquos recordednotes There also turned out to be subtle volume differences whichwere said to have resulted from the combination of the MIDI scoreediting process and the volume compression function in the digitalaudio tape (DAT) recorder used to create stimulus master tapesThese differences were confirmed by careful examination of thewaveforms using a computer oscilloscope Therefore a second gen-eration of S was created by direct numerical substitution of the S+pitches into the MIDI score in reverse order and by recording a newmaster tape with all volume compression disabled The correctionswere verified by waveform analysis

After eight sessions with the second-generat ion S both S+ andS were shortened by the removal of each onersquos distinctive initial noteand seven sessions later they were further shortened by the removal oftheir remaining initial six and final four notes The purpose of thesestimulus contractions was to look for behavioral disruption that might

indicate that the subject had been discriminating the melodies on thebasis of such local features as the absolute pitch of the initial note

Results and DiscussionBeautyrsquos performance inexplicably deteriorated to the

point where he had to be dropped as a subjectFigures 13 and 14 report the performance of Oro the only

fish to complete the melody experiment The data showthat without timbre cues Oro clearly discriminated betweenthe two melodies [in each stimulus condition (ie second-generation S first-note-removed and both-ends-clipped)5 final sessions t(4) gt 10 p lt 001]

Oro responded more to S+ than to S even in the veryfirst session with melodic stimuli Familiarization with theS+ during pretraining could well have contributed to thisresponse bias perhaps partly because music heard in asound-versus-silence context had consistently become theS+ in a subsequent sound-versus-sound discriminationHowever the MIDI artifacts in the first-generation stim-uli might also have played a role

Session 54 in which the corrected S was introducedmarks a significant reduction of the separation between

Figure 12 Experiment 4 (melody discrimination) musical scores of the normal (S+) and pitch-reversed (S )melodies

MUSIC DISCRIMINATIONS BY CARP 351

the S+ and the S nonresponse percentages [two-tailed two-sample t test assuming unequal variances contrasting themean difference between S and S+ nonresponse per-centages before and after the change 8 observations just be-fore the stimulus change vs 8 observations just after t(11) =277 p lt 019] This implies that the rather subtle artifactsin the original S had indeed been exploited as discrimi-nants

One oddity is the fact that although the stimuli changedsignificantly in Sessions 54 (second-generation S ) and62 (removal of the first note of S+ and S ) in each case

a pronounced anomaly in Ororsquos performance occurred inthe following session

Studies of melody discrimination in animals have oftenfound that the behavior was controlled by local featuressuch as timbre pitch register or the absolute pitch of the ini-tial note rather than by the melodic patterning per se(DrsquoAmato amp Salmon 1984 Hulse amp Cynx 1985 Hulseamp Page 1988 Poli amp Previde 1991) (In this paper for theterm local properties I follow the convention of referringnot only to features like distinctive individual notes whichare clearly local in a temporal sense but also to features

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 70

Session Number

S+

S-

= Piano= Down a fifth= wo 1st note= wo 1st 7 amp last 4 notes

S+S-ITI

Figure 13 Experiment 4 (melody discrimination) trials with no responses The MIDI timbre was violin except for 13 sessions ofpiano as marked The corrected S was introduced at Session 54 The first notes of S+ and S were removed at Session 62 The sixinitial and four final notes were removed at Session 69 Crosses denote silence

Figure 14 Experiment 4 (melody discrimination) all responses Sessions terminated with the S+ trial in which the 55th pel-let was dispensed Crosses denote silence

0

20

40

60

All

Pre

sses

0 10 20 30 40 50 60 70

Session Number

S+

S-

Oro

S+S-ITI

352 CHASE

like timbre and pitch register which although recogniz-able in any local segment can be constant over the dura-tion of the stimulus and which therefore might arguablybe called global properties) It should not be surprisingthat with sequential stimuli such as sound animals oftenexploit local features in preference to global pattern fea-tures In the acoustic domain features that are instantly rec-ognizable presumably confer a survival advantage not onlyon listeners but also on creatures in whose interest it is tobe identifiable by sounds they make Oro did not have tim-bre available as a discriminant but there is no conclusiveevidence that he did or did not use other local features andit is not known which if any global features he might haveused

It warrants mention that in this type of discriminationexperiment inaccurate responding need not imply that thesubject is musically insensitive because musical sensitiv-ity can actually confound discriminative accuracy if bothstimuli are musically plausible or stylistically similar In-deed throughout this experiment the stimuli were moni-tored through a speaker in the laboratory office and S+ andS became so familiar and the pitch-track-reversed Ssounded so pleasing that human observers occasionallybecame confused as to which reinforcement contingencywas in force in the tank

The finding that Oro did not need timbre cues to dis-criminate melodies contrasts sharply with the result in ratsreported by Poli and Previde (1991) Using as stimuli for-ward and pitch-track-reversed versions of the melodyldquoFregravere Jacquesrdquo they tested for discrimination on the basisof melodic pattern The rats had neither previous experi-mental experience nor prior familiarity with music In anattempt to preclude the exploitation of local features suchas the absolute pitch of distinctively positioned notes each15-sec stimulus presentation began at a randomly chosenposition within the melody Different groups of subjectswere asked to discriminate two melodic stimuli that dif-fered in melody only in timbre only or in both attributesHowever the stimuli were never heard as unitary melodiesfrom start to finish and were presented in a continuousstream of randomly sequenced exposures with responsesin the presence of S+ being reinforced only on an FR-5schedule This would seem to be such a formidable task asto make it unsurprising that animals failed except when tim-bre a consistent property of every note in each stimuluswas available as a discriminant However Poli and Previdedid suggest that rats might well prove able to discriminatemelodies without timbre cues under other conditions

CONCLUDING REMARKS

The distinction between local features and pattern fea-tures although it arose in connection with melody dis-crimination is equally relevant to the categorization ex-periment To say that in classifying music as blues orclassical the koi might have been responding to deepgeneric attributes is not to say that they were necessarilyusing anything other than local cues because the diag-

nostic property could have been a particular combinationof timbre loudness pitch brief rhythmic or melodic fig-ures and other such local features A human scanning aradio dial requires only a fraction of a second to identifythe genre of a given station hardly enough time for patternfeatures to manifest themselves so a brief sample of musiccould well contain something recognizable to an animalthat had a rote store of auditory feature memories Localfeatures might control classification behavior even whenthere is extensive exposure to a stimulus Conceivably an-imals could acquire a functional understanding of musicentirely on the basis of the distribution and frequency ofvarious combinations of essentially local features with-out regard to the artistic pattern features in terms of whichmusical genres are commonly defined

Prior to this series of experiments the prevailing opinionappeared to be skepticism as to whether koi could dis-criminate one piece of music from another under any cir-cumstances Now it appears that these animals can discrim-inate polyphonic music discriminate melodic patternsand even classify music by artistic genre As far as I knowthese experiments presented the most complex auditorystimuli to which fish have ever been shown capable ofmaking sophisticated discriminative responses Howeverthere remains the task of elucidating the stimulus controlfunctions of the constituents of that complexity such aspattern features local features and simple properties of thestimulus as a whole The present work was intended as ex-ploratory rather than explanatory and the results clearly ex-tend the known envelope of auditory capabilities in fish

REFERENCES

Baron M R (1965) The stimulus stimulus control and generaliza-tion In D I Mostovsky (Ed) Stimulus generalization (pp 62-71)Stanford CA Stanford University Press

Chase A R amp Hill W (1999) Reliable operant apparatus for fishAudio stimulus generator response button and pellet-dispensing nip-ple Behavior Research Methods Instruments amp Computers 31 470-478

Coombs S Jannsen J amp Montgomery J C (1992) Functional andevolutionary implications of peripheral diversity in lateral line sys-tems In D B Webster R R Fay amp A N Popper (Eds) The evolu-tionary biology of hearing (pp 267-294) New York Springer-Verlag

DrsquoAmato M R amp Salmon D P (1982) Tune discrimination in mon-keys (Cebus apella) and rats Animal Learning amp Behavior 10 126-134

DrsquoAmato M R amp Salmon D P (1984) Processing of complex au-ditory stimuli (tunes) by rats and monkeys (Cebus apella) AnimalLearning amp Behavior 12 184-194

Fay R R (1988) Hearing in vertebrates A psychophysics data-bookWinnetka IL Hill-Fay Associates

Fay R R (1992) Analytic listening in goldfish Hearing Research 59101-107

Fay R R (1994) Perception of temporal acoustic patterns by the gold-fish (Carassius auratus) Hearing Research 76 158-172

Fay R R (1995) Perception of spectrally and temporally complexsounds by the goldfish (Carassius auratus) Hearing Research 89146-154

Fay R R (1998) Auditory stream segregation in goldfish (Carassiusauratus) Hearing Research 120 69-76

Fay R R amp Ream T J (1986) Acoustic response and tuning in sac-cular nerve fibers of the goldfish (Carassius auratus) Journal of theAcoustical Society of America 79 1883-1895

Hartman W M (1988) Pitch perception and the segregation and inte-

MUSIC DISCRIMINATIONS BY CARP 343

sensitive the more information is available from which todiscern patterns and changes indications that animalslearn more than the minimal solution to classificationproblems involving complex stimuli suggest that as com-pared with trying to ignore as much as possible of theworld evolution favors embracing its complexity

EXPERIMENT 2 Iterated Reversals

MethodThe first categorization session in which the contingencies were

reversed had served as a control procedure This experimental con-

0

25

50

75

100

Tri

als

wit

h N

o P

ress

Beauty

S-

S+

0

25

50

75

100

Tri

als

wit

h N

o P

ress

Oro

S-

S+

200 Hz filter

0

25

50

75

100

Tri

als

wit

h N

o P

ress

40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

Session Number

Pepi

S+

S-

S+ S- ITI

Figure 5 Experiment 1 (categorization) percentages of S+ (blues) and S (classical) trials and intertrial intervals (ITIs silence)during which the fish did not press the button at all plotted for each session The greater the separation between a sessionrsquos S+ andS nonresponse percentages the more clearly the subject was discriminating the stimuli as opposed to responding indiscriminatelyand receiving feedback from the reinforcement contingency The boxed data points indicate probe sessions The bar from Sessions147ndash149 shows where the 200-Hz low-frequency cutoff filter was used The circled data points (Session 182) indicate the first control-by-reversal session In the reversal sessions (182ndash192) S+ (still represented by open squares) was now classical music whereas S (stillrepresented by filled triangles) was blues Crosses denote silence

344 CHASE

dition (ie with blues now the S and classical now the S+) wasthen extended into an iterated-reversal experiment The primary goalwas to test koi in reversal learning with complex auditory stimuliafter having found nothing in the literature on the subject of auditoryreversal learning in fish

A secondary goal was to prepare for a planned experiment with aclassification procedure involving two visually distinct buttons withresponses on a particular button to be reinforced only in the presenceof a particular type of music The rim of the original button had beenmachined from black Delrin A new rim was made from an ivory-

colored blank of the same plastic and installed after six sessions ofthe unsignaled reversal (ie no change in the button) Thereafterrim color alternated in synchrony with contingency reversals withblack and ivory signaling that S+ was blues and classical respec-tively The fish would experience a total of four color changes thefirst of which did not signal a contingency change

The sessions were terminated by either the trial in which the 50thpellet was dispensed or an elapsed time of 90 min whichever camefirst Altogether there were 119 sessions spanning four reversals(see Figure 4)

Figure 6 Experiment 1 (categorization) all responses Number of responses in each session during blues trials classical trials andintertrial intervals (ITIs) Under the reversal condition that began with Session 182 blues became S and classical became S+ Bluesresponse counts above 50 reflect the onset of extinction Reversal sessions in which the classical response count was less than 50 wereterminated at 90 min Crosses denote silence

0

20

40

60

80

100

120

All

Pre

sses

40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

Session Number

Pepi

0

20

40

60

80

100

120

All

Pre

sses

ITI

Oro

0

20

40

60

80

100

120

All

Pre

sses

BeautyBluesClassicalITI

MUSIC DISCRIMINATIONS BY CARP 345

Just before the first reversal the stimuli had been a House of Bluescompilation (S+) and a baroque horn compilation (S ) When thecontingencies were reversed making blues S and classical S+both stimuli were also replaced The first reversal stimuli were Bachoboe concertos (S+) and John Lee Hookerrsquos Real Folks Blues (S )both very familiar to the fish In the next three phases of the first re-versal three additional pairs of familiar CDs were used In the fifthand final phase of the first reversal the fish were exposed to entirelynovel stimuli (S The Blues Story compilation S+ Bach triosonatas) As in the categorization study the first session with novelstimuli (Session 224) served as a probe testing for open-ended cat-egorization Blues and classical successively exchanged roles as S+and S in three additional reversal phases all using familiar stim-uli As can be seen in Figure 4 when the first and third reversals oc-curred at least one stimulus CD changed as well The final reversalbrought the contingencies back to where they had been before thefirst reversalmdashnamely with blues as S+ and classical as S

ResultsThe first reversal (Session 182) produced considerable

behavioral disruption and erroneous responding (see Fig-

ures 8 and 9) In the first 6ndash9 sessions the increase in re-sponding to the genre newly become S+ was insufficientfor any fish to earn 50 reinforcements within the 90-mintime limit (Figure 8) Beauty and Oro steadily improvedand were reliably discriminating by the 16th and 23rd ses-sions respectively Pepi achieved significance by Session 9but then his performance was substandard until Session 27[5 sessions ts(4) gt 229 p lt 010 p lt 009 and p lt 042respectively] Near the end of the first reversal the probesession (224) revealed that the classification behavior ex-hibited by Beauty and Oro was clearly open-ended catego-rization With each successive reversal it took fewer sessionsfor Beauty and Oro to demonstrate clear discrimination(Figures 9 and 10) Even Pepi eventually learned each re-versalmdashalbeit while continuing to call attention to the ex-istence of considerable and systematic individual differ-ences among fish In Figure 9 least-squares regressionlines are plotted for S nonresponse data and as is shownin Figure 10 their slopes indicate improvement rates of

0

50

100 Beauty

0

50

100 Oro

0

50

100

Mean 115 120 131 138 152 157 163 168 177 Mean

Probe Sessions (Novel CDs) Probes

Pepi

Non probes

S+S-ITI

Tri

als

wit

h N

o P

ress

Tri

als

wit

h N

o P

ress

Tri

als

wit

h N

o P

res

s

Figure 7 Experiment 1 (categorization) categorization performance during probe ses-sions (ie all-novel stimuli) percentages of S+ trials intertrial intervals (ITI) and S tri-als in which the fish did not respond Black bars indicate S+ gray bars indicate S andwhite bars indicate ITI Low nonresponse percentages for S+ indicate a high likelihoodof responding during S+ whereas high nonresponse percentages for S indicate that thefish tended to ignore the button during S The leftmost ldquoMeanrdquo bars show the averagesof all the nonprobe sessions in the session range 115ndash181 and the rightmost ldquoMeanrdquo barsshow the averages of the probe sessions

346 CHASE

08 and 11 per session for Beauty and Oro respec-tively during the first reversal (Sessions 182ndash238) Overthe final 5 sessions of each reversal phase discriminationby Beauty Oro and Pepi was statistically significant at

levels always better than p lt 010 p lt 016 and p lt 042respectively [ts(4) gt 229] It can be seen in Figure 8 thatwith each reversal the increase in responding to the new S+was generally faster than the extinction to the former S+

0

20

40

60

80

100

120

All

Pre

sses

Beauty

0

20

40

60

80

100

120

All

Pre

sses

Oro

ITI

Session Number

blues

classical classicalbluesblues

0

20

40

60

80

100

120

All

Pre

sses

150 175 200 225 250 275 300

Pepi

classical

BluesClassical

Figure 8 Experiment 2 (iterated reversals) counts of all responses by session Note that in graphs of reversal data the symbols con-sistently indicate genre (open squares blues filled triangles classical) not stimulus semantics (S+ or S ) which of course change ateach reversal This convention highlights the fluctuating response pattern associated with each genre longitudinally as successive re-versals of reinforcement contingency produce disruption and then learning with increasing efficiency The primary session termina-tion trigger was the trial on which the 50th pellet was delivered but in the early sessions of the first reversal no subject made as manyas 50 ldquocorrectrdquo responses to the former S within the session time limit even while responding many more than 50 times without re-inforcement to the former S+ Note that the extinction-induced response frenzy associated with a genrersquos suddenly becoming S de-creases with each reversal Crosses denote silence

MUSIC DISCRIMINATIONS BY CARP 347

EXPERIMENT 3Transition to Synthetic Keyboard Music and

Polyphonic Discrimination with Identical Timbre

The next step was to try to extend the learned classifi-cation of natural music to MIDI (Musical Instrument Dig-

ital Interface) synthesized music in which S+ and Swere not distinguishable by timbre

MethodPretraining After the iterated-reversal experiment the fish re-

mained in the homeexperimental tank from which all the appara-tus had been removed and they were not exposed to music or to anytraining or experimental procedures for a period of 10 months The

Tri

als

wit

h N

o P

ress

0

25

50

75

100

Reversals

Oro

classical

blues

classical

classical

blues

bluesTri

als

wit

h N

o P

ress

0

25

50

75

100

150 200 250 300

Session Number

Pepi

0

25

50

75

100

First Reversal

Beauty

Probe

Tri

als

wit

h N

o P

ress

ITI

BluesClassicalITI

Figure 9 Experiment 2 (iterated reversals) percentages of trials with no responses by session Note the increasingly efficient learn-ing of nonresponding to each former S+ as shown by the increasing slopes of the least-squares regression lines Session 224 (dashedline) was a probe the accurate discrimination of entirely novel stimuli indicates that the fish were performing open-ended catego-rization Crosses denote silence

348 CHASE

work resumed with a reintroduction to the apparatus and protocol asleft off at the end of the fourth and final reversalmdashthat is with S+and S being blues and classical respectively However the fishwere also being prepared to encounter the synthetic stimuli that werebeing created at that time which consisted of a single short piecefrom each genre rather than a collection comparable in duration andvariety with the commercial CDs used previously Therefore in pre-training the stimuli were the same two CDs the subjects had lastheard (see Figure 4 Session 300) but only a single track from eachS was an excerpt from a Bach oboe concerto S+ was the John LeeHooker song ldquoOne Bourbon One Scotch and One Beerrdquo of whicha synthesized version was in the works

Initially Beauty and Oro seemed to manifest effects of the longhiatus in the form of low response rates (not enough to earn 50 pel-lets in a session) and some transient difficulties operating the buttonand taking pellets from the nipple However even allowing for somerelearning and the reduced size of the new stimuli the immediacywith which all 3 subjects exhibited highly accurate discriminationsuggests that the original discrimination training had been retained(compare the leftmost sessions in Figure 11 with the rightmost inFigure 9)

Procedure The new stimuli were musically simplif ied MIDIkeyboard renditions of music of the types the f ish had alreadylearned to classify S+ was the familiar blues song described aboveand S was the unfamiliar Fugue 2 from Book I of Bachrsquos Well-Tempered Clavier To minimize the presence of extraneous cues allthe performances were done by the same musician with the sameequipment (a Kurzweil Model k2000vp keyboard Young Chang Re-search and Development Institute Waltham MA) the same se-quencing software (Studio Vision Pro Version 40 Opcode SystemsNashville TN) and the same settings for volume and for timbre(acoustic piano) Because the new stimuli were so short that theywould repeat after only a few trials rote memory could play a rolein their discrimination and thus the operative level of stimulus con-trol was being allowed to potentially regress from categorization todiscrimination

The initial synthetic stimuli turned out to trigger a deteriorationin classification accuracy (Figure 11 Session 13) It seemed possi-ble that this was an artifact of the musical translation process be-cause even humans had some difficulty recognizing the John LeeHooker song in synthetic form It had gone from bluesy to bouncyits original bass inflections were absent and there was no melodicvoice comparable with that of the singer Therefore at Session 24 Iintroduced a second generation of stimuli S+ remained the samepiece but the performance was somewhat more faithful to themodel The old S (the Bach fugue) had been much shorter than S+and thus had been repeating more often so it was replaced by a syn-

thesized rendition of the f irst movement of Vivaldirsquos ConcertoGrosso in A minor Opus 3 No 6 whose duration more closelymatched that of S+ In addition the timbre of the blues was changedfrom acoustic piano to rock piano thus adding timbre as an availablediscriminant However from Session 47 until the end of the experi-ment S+ and S again had timbre in common specifically rockpiano (starting in Session 47) chiffloot (starting in Session 55) andguitar (starting in Session 62)

ResultsWith the first presentations in a synthetic timbre discrim-

ination accuracy deteriorated (Figure 11 Sessions 13ndash23)perhaps because the first synthetic S+ was not a good enoughexemplar of the blues genre Pepi essentially ceased re-sponding during this time and had to be dropped from thestudy Starting at Session 24 with improved stimuli and adifference in timbre between S+ and S the behavior ofboth remaining subjects immediately changed and there-after their discriminative accuracy improved continually

When S+ and S were again made identical in timbre(Session 47) accurate classification persisted despite aperformance decrement probably related to the loss of asalient cue When the same pair of MIDI sequences waspresented in additional timbres generalization of accurateclassification to the new sounds appeared seamless The datafrom Session 47 and onward demonstrate [Sessions 18ts(17) gt 16 ps lt 001] that koi are capable of discriminat-ing polyphonic music on the basis of features other thanthe timbre of individual tone sources

EXPERIMENT 4 Discrimination of Melodies

Without Timbre Cues

After observing that instrumental timbre seemed not tobe a necessary discriminant in polyphonic music I inves-tigated whether timbre was necessary for koi to discrimi-nate single-voice musicmdashthat is melodies

MethodIn order to familiarize the subjects with the S+ melody and also

in hopes of rehabilitating Pepi this experiment began with severalsessions of collective exposure to a sound-versus-silence contin-gency CRF signaled by the music that would later be the S+ in thesound-versus-sound discrimination alternated with extinction sig-naled by silence In this group pretraining Pepi was observed bothpressing the button and taking pellets from the nipple but when sub-sequently isolated for melody discrimination sessions he consis-tently shied away from the nipple and again had to be dropped as asubject

The stimuli for the melody discrimination experiment (Figure 12)were all derived from the theme from Paganinirsquos 24th Caprice forsolo violin which is perhaps best known from Rachmaninoff rsquosldquoRhapsody on a Theme by Paganinirdquo S+ was the original melody asperformed on the MIDI keyboard S was derived from S+ by usingthe transformation described by Poli and Previde (1991) By using acomputer to modify the MIDI score S+rsquos order of pitches was re-versed whereas its original order of note durations was retained Inother words the first note of S got the duration of S+rsquos first notebut the pitch of S+rsquos last note the second note of S got the durationof S+rsquos second note but the pitch of S+rsquos next-to-last note and so onThis procedure can be thought of as retaining the rhythm track while

0

1

2

3S

lop

e (

ch

ang

ese

ssio

n)

1 2 3 4

Reversal Number

OroBeauty

Pepi

Figure 10 Experiment 2 (iterated reversals) improvementtrends For Beauty and Oro the improvement rate (Figure 9 re-gression line slopes percentage of nonresponse S trials per ses-sion) increases with each reversal

MUSIC DISCRIMINATIONS BY CARP 349

reversing the pitch track The result is two stimuli that are ldquoidenticalwith respect to their mean frequency note duration and rhythm butnoticeably different in their melodic patternsrdquo (Poli amp Previde 1991p 12) Such a pitch-track-reversed melody differs from a completelybackwards melody only in rhythm sacrificing the linkage betweeneach pitch and its original duration in order to preserve the originalsequence of durations per se (If the original melodymdashunlike the

Rachmaninoffmdashhas a palindromic rhythm track the pitch-track -reversed melody and the completely backwards melody are identical)The melodies were recorded using the same MIDI apparatus as thatdescribed above To enhance clarity the tempo was somewhat slowerthan that of the usual piano performance

Over the course of 53 sessions the instrumental timbre alternatedsix times between strings and acoustic piano but in any given ses-

0

25

50

75

100

Tri

als

wit

h N

o P

res

s

S+

ITI

S-

Beauty

0

25

50

75

100

Tri

als

wit

h N

o P

ress

S+

ITI

S-

Oro

Same Timbre Different Timbre Same Timbre

S+S-ITI

Pepi ceased responding

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 Session Number

S+

ITI

S-

Pepi

Figure 11 Experiment 3 (transition to MIDI and timbre study) percentages of S+ and S trials dur-ing which the fish did not press the button During the first 12 sessions the stimuli consisted of a singletrack from each of the two commercial recordings the subjects had last heard 10 months earlier at theconclusion of the iterated-reversal experiment the immediate resumption of accurate discrimination sug-gests long-term memory of training The circled data points (Sessions 13 and 24) indicate the introduc-tion of the first- and second-generation synthetic music From Session 47 until the end of the experimentS+ and S had identical timbre each boxed data point pair indicates the first presentation of a new tim-bre Session 47 rock piano Session 55 chiffloot and Session 62 guitar Crosses denote silence

350 CHASE

sion S+ and S always had the same timbre The discrimination pro-tocol was unchanged from the previous experiments except that thesession termination trigger was raised from 50 to 55 pellets As a pre-liminary test for a possible perceptual invariance (Hulse Takeuchi ampBraaten 1992) S+ was transposed down a fifth in Sessions 51ndash52

After 53 sessions it was discovered that the MIDI technology hadintroduced artifactual differences between S+ and S A musicallyattuned visitor to the lab detected minor variations in note durationsbetween the two stimuli which apparently had resulted from incor-rect handling of the attackndashsustainndashdecay envelopes of S+rsquos recordednotes There also turned out to be subtle volume differences whichwere said to have resulted from the combination of the MIDI scoreediting process and the volume compression function in the digitalaudio tape (DAT) recorder used to create stimulus master tapesThese differences were confirmed by careful examination of thewaveforms using a computer oscilloscope Therefore a second gen-eration of S was created by direct numerical substitution of the S+pitches into the MIDI score in reverse order and by recording a newmaster tape with all volume compression disabled The correctionswere verified by waveform analysis

After eight sessions with the second-generat ion S both S+ andS were shortened by the removal of each onersquos distinctive initial noteand seven sessions later they were further shortened by the removal oftheir remaining initial six and final four notes The purpose of thesestimulus contractions was to look for behavioral disruption that might

indicate that the subject had been discriminating the melodies on thebasis of such local features as the absolute pitch of the initial note

Results and DiscussionBeautyrsquos performance inexplicably deteriorated to the

point where he had to be dropped as a subjectFigures 13 and 14 report the performance of Oro the only

fish to complete the melody experiment The data showthat without timbre cues Oro clearly discriminated betweenthe two melodies [in each stimulus condition (ie second-generation S first-note-removed and both-ends-clipped)5 final sessions t(4) gt 10 p lt 001]

Oro responded more to S+ than to S even in the veryfirst session with melodic stimuli Familiarization with theS+ during pretraining could well have contributed to thisresponse bias perhaps partly because music heard in asound-versus-silence context had consistently become theS+ in a subsequent sound-versus-sound discriminationHowever the MIDI artifacts in the first-generation stim-uli might also have played a role

Session 54 in which the corrected S was introducedmarks a significant reduction of the separation between

Figure 12 Experiment 4 (melody discrimination) musical scores of the normal (S+) and pitch-reversed (S )melodies

MUSIC DISCRIMINATIONS BY CARP 351

the S+ and the S nonresponse percentages [two-tailed two-sample t test assuming unequal variances contrasting themean difference between S and S+ nonresponse per-centages before and after the change 8 observations just be-fore the stimulus change vs 8 observations just after t(11) =277 p lt 019] This implies that the rather subtle artifactsin the original S had indeed been exploited as discrimi-nants

One oddity is the fact that although the stimuli changedsignificantly in Sessions 54 (second-generation S ) and62 (removal of the first note of S+ and S ) in each case

a pronounced anomaly in Ororsquos performance occurred inthe following session

Studies of melody discrimination in animals have oftenfound that the behavior was controlled by local featuressuch as timbre pitch register or the absolute pitch of the ini-tial note rather than by the melodic patterning per se(DrsquoAmato amp Salmon 1984 Hulse amp Cynx 1985 Hulseamp Page 1988 Poli amp Previde 1991) (In this paper for theterm local properties I follow the convention of referringnot only to features like distinctive individual notes whichare clearly local in a temporal sense but also to features

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 70

Session Number

S+

S-

= Piano= Down a fifth= wo 1st note= wo 1st 7 amp last 4 notes

S+S-ITI

Figure 13 Experiment 4 (melody discrimination) trials with no responses The MIDI timbre was violin except for 13 sessions ofpiano as marked The corrected S was introduced at Session 54 The first notes of S+ and S were removed at Session 62 The sixinitial and four final notes were removed at Session 69 Crosses denote silence

Figure 14 Experiment 4 (melody discrimination) all responses Sessions terminated with the S+ trial in which the 55th pel-let was dispensed Crosses denote silence

0

20

40

60

All

Pre

sses

0 10 20 30 40 50 60 70

Session Number

S+

S-

Oro

S+S-ITI

352 CHASE

like timbre and pitch register which although recogniz-able in any local segment can be constant over the dura-tion of the stimulus and which therefore might arguablybe called global properties) It should not be surprisingthat with sequential stimuli such as sound animals oftenexploit local features in preference to global pattern fea-tures In the acoustic domain features that are instantly rec-ognizable presumably confer a survival advantage not onlyon listeners but also on creatures in whose interest it is tobe identifiable by sounds they make Oro did not have tim-bre available as a discriminant but there is no conclusiveevidence that he did or did not use other local features andit is not known which if any global features he might haveused

It warrants mention that in this type of discriminationexperiment inaccurate responding need not imply that thesubject is musically insensitive because musical sensitiv-ity can actually confound discriminative accuracy if bothstimuli are musically plausible or stylistically similar In-deed throughout this experiment the stimuli were moni-tored through a speaker in the laboratory office and S+ andS became so familiar and the pitch-track-reversed Ssounded so pleasing that human observers occasionallybecame confused as to which reinforcement contingencywas in force in the tank

The finding that Oro did not need timbre cues to dis-criminate melodies contrasts sharply with the result in ratsreported by Poli and Previde (1991) Using as stimuli for-ward and pitch-track-reversed versions of the melodyldquoFregravere Jacquesrdquo they tested for discrimination on the basisof melodic pattern The rats had neither previous experi-mental experience nor prior familiarity with music In anattempt to preclude the exploitation of local features suchas the absolute pitch of distinctively positioned notes each15-sec stimulus presentation began at a randomly chosenposition within the melody Different groups of subjectswere asked to discriminate two melodic stimuli that dif-fered in melody only in timbre only or in both attributesHowever the stimuli were never heard as unitary melodiesfrom start to finish and were presented in a continuousstream of randomly sequenced exposures with responsesin the presence of S+ being reinforced only on an FR-5schedule This would seem to be such a formidable task asto make it unsurprising that animals failed except when tim-bre a consistent property of every note in each stimuluswas available as a discriminant However Poli and Previdedid suggest that rats might well prove able to discriminatemelodies without timbre cues under other conditions

CONCLUDING REMARKS

The distinction between local features and pattern fea-tures although it arose in connection with melody dis-crimination is equally relevant to the categorization ex-periment To say that in classifying music as blues orclassical the koi might have been responding to deepgeneric attributes is not to say that they were necessarilyusing anything other than local cues because the diag-

nostic property could have been a particular combinationof timbre loudness pitch brief rhythmic or melodic fig-ures and other such local features A human scanning aradio dial requires only a fraction of a second to identifythe genre of a given station hardly enough time for patternfeatures to manifest themselves so a brief sample of musiccould well contain something recognizable to an animalthat had a rote store of auditory feature memories Localfeatures might control classification behavior even whenthere is extensive exposure to a stimulus Conceivably an-imals could acquire a functional understanding of musicentirely on the basis of the distribution and frequency ofvarious combinations of essentially local features with-out regard to the artistic pattern features in terms of whichmusical genres are commonly defined

Prior to this series of experiments the prevailing opinionappeared to be skepticism as to whether koi could dis-criminate one piece of music from another under any cir-cumstances Now it appears that these animals can discrim-inate polyphonic music discriminate melodic patternsand even classify music by artistic genre As far as I knowthese experiments presented the most complex auditorystimuli to which fish have ever been shown capable ofmaking sophisticated discriminative responses Howeverthere remains the task of elucidating the stimulus controlfunctions of the constituents of that complexity such aspattern features local features and simple properties of thestimulus as a whole The present work was intended as ex-ploratory rather than explanatory and the results clearly ex-tend the known envelope of auditory capabilities in fish

REFERENCES

Baron M R (1965) The stimulus stimulus control and generaliza-tion In D I Mostovsky (Ed) Stimulus generalization (pp 62-71)Stanford CA Stanford University Press

Chase A R amp Hill W (1999) Reliable operant apparatus for fishAudio stimulus generator response button and pellet-dispensing nip-ple Behavior Research Methods Instruments amp Computers 31 470-478

Coombs S Jannsen J amp Montgomery J C (1992) Functional andevolutionary implications of peripheral diversity in lateral line sys-tems In D B Webster R R Fay amp A N Popper (Eds) The evolu-tionary biology of hearing (pp 267-294) New York Springer-Verlag

DrsquoAmato M R amp Salmon D P (1982) Tune discrimination in mon-keys (Cebus apella) and rats Animal Learning amp Behavior 10 126-134

DrsquoAmato M R amp Salmon D P (1984) Processing of complex au-ditory stimuli (tunes) by rats and monkeys (Cebus apella) AnimalLearning amp Behavior 12 184-194

Fay R R (1988) Hearing in vertebrates A psychophysics data-bookWinnetka IL Hill-Fay Associates

Fay R R (1992) Analytic listening in goldfish Hearing Research 59101-107

Fay R R (1994) Perception of temporal acoustic patterns by the gold-fish (Carassius auratus) Hearing Research 76 158-172

Fay R R (1995) Perception of spectrally and temporally complexsounds by the goldfish (Carassius auratus) Hearing Research 89146-154

Fay R R (1998) Auditory stream segregation in goldfish (Carassiusauratus) Hearing Research 120 69-76

Fay R R amp Ream T J (1986) Acoustic response and tuning in sac-cular nerve fibers of the goldfish (Carassius auratus) Journal of theAcoustical Society of America 79 1883-1895

Hartman W M (1988) Pitch perception and the segregation and inte-

344 CHASE

dition (ie with blues now the S and classical now the S+) wasthen extended into an iterated-reversal experiment The primary goalwas to test koi in reversal learning with complex auditory stimuliafter having found nothing in the literature on the subject of auditoryreversal learning in fish

A secondary goal was to prepare for a planned experiment with aclassification procedure involving two visually distinct buttons withresponses on a particular button to be reinforced only in the presenceof a particular type of music The rim of the original button had beenmachined from black Delrin A new rim was made from an ivory-

colored blank of the same plastic and installed after six sessions ofthe unsignaled reversal (ie no change in the button) Thereafterrim color alternated in synchrony with contingency reversals withblack and ivory signaling that S+ was blues and classical respec-tively The fish would experience a total of four color changes thefirst of which did not signal a contingency change

The sessions were terminated by either the trial in which the 50thpellet was dispensed or an elapsed time of 90 min whichever camefirst Altogether there were 119 sessions spanning four reversals(see Figure 4)

Figure 6 Experiment 1 (categorization) all responses Number of responses in each session during blues trials classical trials andintertrial intervals (ITIs) Under the reversal condition that began with Session 182 blues became S and classical became S+ Bluesresponse counts above 50 reflect the onset of extinction Reversal sessions in which the classical response count was less than 50 wereterminated at 90 min Crosses denote silence

0

20

40

60

80

100

120

All

Pre

sses

40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

Session Number

Pepi

0

20

40

60

80

100

120

All

Pre

sses

ITI

Oro

0

20

40

60

80

100

120

All

Pre

sses

BeautyBluesClassicalITI

MUSIC DISCRIMINATIONS BY CARP 345

Just before the first reversal the stimuli had been a House of Bluescompilation (S+) and a baroque horn compilation (S ) When thecontingencies were reversed making blues S and classical S+both stimuli were also replaced The first reversal stimuli were Bachoboe concertos (S+) and John Lee Hookerrsquos Real Folks Blues (S )both very familiar to the fish In the next three phases of the first re-versal three additional pairs of familiar CDs were used In the fifthand final phase of the first reversal the fish were exposed to entirelynovel stimuli (S The Blues Story compilation S+ Bach triosonatas) As in the categorization study the first session with novelstimuli (Session 224) served as a probe testing for open-ended cat-egorization Blues and classical successively exchanged roles as S+and S in three additional reversal phases all using familiar stim-uli As can be seen in Figure 4 when the first and third reversals oc-curred at least one stimulus CD changed as well The final reversalbrought the contingencies back to where they had been before thefirst reversalmdashnamely with blues as S+ and classical as S

ResultsThe first reversal (Session 182) produced considerable

behavioral disruption and erroneous responding (see Fig-

ures 8 and 9) In the first 6ndash9 sessions the increase in re-sponding to the genre newly become S+ was insufficientfor any fish to earn 50 reinforcements within the 90-mintime limit (Figure 8) Beauty and Oro steadily improvedand were reliably discriminating by the 16th and 23rd ses-sions respectively Pepi achieved significance by Session 9but then his performance was substandard until Session 27[5 sessions ts(4) gt 229 p lt 010 p lt 009 and p lt 042respectively] Near the end of the first reversal the probesession (224) revealed that the classification behavior ex-hibited by Beauty and Oro was clearly open-ended catego-rization With each successive reversal it took fewer sessionsfor Beauty and Oro to demonstrate clear discrimination(Figures 9 and 10) Even Pepi eventually learned each re-versalmdashalbeit while continuing to call attention to the ex-istence of considerable and systematic individual differ-ences among fish In Figure 9 least-squares regressionlines are plotted for S nonresponse data and as is shownin Figure 10 their slopes indicate improvement rates of

0

50

100 Beauty

0

50

100 Oro

0

50

100

Mean 115 120 131 138 152 157 163 168 177 Mean

Probe Sessions (Novel CDs) Probes

Pepi

Non probes

S+S-ITI

Tri

als

wit

h N

o P

ress

Tri

als

wit

h N

o P

ress

Tri

als

wit

h N

o P

res

s

Figure 7 Experiment 1 (categorization) categorization performance during probe ses-sions (ie all-novel stimuli) percentages of S+ trials intertrial intervals (ITI) and S tri-als in which the fish did not respond Black bars indicate S+ gray bars indicate S andwhite bars indicate ITI Low nonresponse percentages for S+ indicate a high likelihoodof responding during S+ whereas high nonresponse percentages for S indicate that thefish tended to ignore the button during S The leftmost ldquoMeanrdquo bars show the averagesof all the nonprobe sessions in the session range 115ndash181 and the rightmost ldquoMeanrdquo barsshow the averages of the probe sessions

346 CHASE

08 and 11 per session for Beauty and Oro respec-tively during the first reversal (Sessions 182ndash238) Overthe final 5 sessions of each reversal phase discriminationby Beauty Oro and Pepi was statistically significant at

levels always better than p lt 010 p lt 016 and p lt 042respectively [ts(4) gt 229] It can be seen in Figure 8 thatwith each reversal the increase in responding to the new S+was generally faster than the extinction to the former S+

0

20

40

60

80

100

120

All

Pre

sses

Beauty

0

20

40

60

80

100

120

All

Pre

sses

Oro

ITI

Session Number

blues

classical classicalbluesblues

0

20

40

60

80

100

120

All

Pre

sses

150 175 200 225 250 275 300

Pepi

classical

BluesClassical

Figure 8 Experiment 2 (iterated reversals) counts of all responses by session Note that in graphs of reversal data the symbols con-sistently indicate genre (open squares blues filled triangles classical) not stimulus semantics (S+ or S ) which of course change ateach reversal This convention highlights the fluctuating response pattern associated with each genre longitudinally as successive re-versals of reinforcement contingency produce disruption and then learning with increasing efficiency The primary session termina-tion trigger was the trial on which the 50th pellet was delivered but in the early sessions of the first reversal no subject made as manyas 50 ldquocorrectrdquo responses to the former S within the session time limit even while responding many more than 50 times without re-inforcement to the former S+ Note that the extinction-induced response frenzy associated with a genrersquos suddenly becoming S de-creases with each reversal Crosses denote silence

MUSIC DISCRIMINATIONS BY CARP 347

EXPERIMENT 3Transition to Synthetic Keyboard Music and

Polyphonic Discrimination with Identical Timbre

The next step was to try to extend the learned classifi-cation of natural music to MIDI (Musical Instrument Dig-

ital Interface) synthesized music in which S+ and Swere not distinguishable by timbre

MethodPretraining After the iterated-reversal experiment the fish re-

mained in the homeexperimental tank from which all the appara-tus had been removed and they were not exposed to music or to anytraining or experimental procedures for a period of 10 months The

Tri

als

wit

h N

o P

ress

0

25

50

75

100

Reversals

Oro

classical

blues

classical

classical

blues

bluesTri

als

wit

h N

o P

ress

0

25

50

75

100

150 200 250 300

Session Number

Pepi

0

25

50

75

100

First Reversal

Beauty

Probe

Tri

als

wit

h N

o P

ress

ITI

BluesClassicalITI

Figure 9 Experiment 2 (iterated reversals) percentages of trials with no responses by session Note the increasingly efficient learn-ing of nonresponding to each former S+ as shown by the increasing slopes of the least-squares regression lines Session 224 (dashedline) was a probe the accurate discrimination of entirely novel stimuli indicates that the fish were performing open-ended catego-rization Crosses denote silence

348 CHASE

work resumed with a reintroduction to the apparatus and protocol asleft off at the end of the fourth and final reversalmdashthat is with S+and S being blues and classical respectively However the fishwere also being prepared to encounter the synthetic stimuli that werebeing created at that time which consisted of a single short piecefrom each genre rather than a collection comparable in duration andvariety with the commercial CDs used previously Therefore in pre-training the stimuli were the same two CDs the subjects had lastheard (see Figure 4 Session 300) but only a single track from eachS was an excerpt from a Bach oboe concerto S+ was the John LeeHooker song ldquoOne Bourbon One Scotch and One Beerrdquo of whicha synthesized version was in the works

Initially Beauty and Oro seemed to manifest effects of the longhiatus in the form of low response rates (not enough to earn 50 pel-lets in a session) and some transient difficulties operating the buttonand taking pellets from the nipple However even allowing for somerelearning and the reduced size of the new stimuli the immediacywith which all 3 subjects exhibited highly accurate discriminationsuggests that the original discrimination training had been retained(compare the leftmost sessions in Figure 11 with the rightmost inFigure 9)

Procedure The new stimuli were musically simplif ied MIDIkeyboard renditions of music of the types the f ish had alreadylearned to classify S+ was the familiar blues song described aboveand S was the unfamiliar Fugue 2 from Book I of Bachrsquos Well-Tempered Clavier To minimize the presence of extraneous cues allthe performances were done by the same musician with the sameequipment (a Kurzweil Model k2000vp keyboard Young Chang Re-search and Development Institute Waltham MA) the same se-quencing software (Studio Vision Pro Version 40 Opcode SystemsNashville TN) and the same settings for volume and for timbre(acoustic piano) Because the new stimuli were so short that theywould repeat after only a few trials rote memory could play a rolein their discrimination and thus the operative level of stimulus con-trol was being allowed to potentially regress from categorization todiscrimination

The initial synthetic stimuli turned out to trigger a deteriorationin classification accuracy (Figure 11 Session 13) It seemed possi-ble that this was an artifact of the musical translation process be-cause even humans had some difficulty recognizing the John LeeHooker song in synthetic form It had gone from bluesy to bouncyits original bass inflections were absent and there was no melodicvoice comparable with that of the singer Therefore at Session 24 Iintroduced a second generation of stimuli S+ remained the samepiece but the performance was somewhat more faithful to themodel The old S (the Bach fugue) had been much shorter than S+and thus had been repeating more often so it was replaced by a syn-

thesized rendition of the f irst movement of Vivaldirsquos ConcertoGrosso in A minor Opus 3 No 6 whose duration more closelymatched that of S+ In addition the timbre of the blues was changedfrom acoustic piano to rock piano thus adding timbre as an availablediscriminant However from Session 47 until the end of the experi-ment S+ and S again had timbre in common specifically rockpiano (starting in Session 47) chiffloot (starting in Session 55) andguitar (starting in Session 62)

ResultsWith the first presentations in a synthetic timbre discrim-

ination accuracy deteriorated (Figure 11 Sessions 13ndash23)perhaps because the first synthetic S+ was not a good enoughexemplar of the blues genre Pepi essentially ceased re-sponding during this time and had to be dropped from thestudy Starting at Session 24 with improved stimuli and adifference in timbre between S+ and S the behavior ofboth remaining subjects immediately changed and there-after their discriminative accuracy improved continually

When S+ and S were again made identical in timbre(Session 47) accurate classification persisted despite aperformance decrement probably related to the loss of asalient cue When the same pair of MIDI sequences waspresented in additional timbres generalization of accurateclassification to the new sounds appeared seamless The datafrom Session 47 and onward demonstrate [Sessions 18ts(17) gt 16 ps lt 001] that koi are capable of discriminat-ing polyphonic music on the basis of features other thanthe timbre of individual tone sources

EXPERIMENT 4 Discrimination of Melodies

Without Timbre Cues

After observing that instrumental timbre seemed not tobe a necessary discriminant in polyphonic music I inves-tigated whether timbre was necessary for koi to discrimi-nate single-voice musicmdashthat is melodies

MethodIn order to familiarize the subjects with the S+ melody and also

in hopes of rehabilitating Pepi this experiment began with severalsessions of collective exposure to a sound-versus-silence contin-gency CRF signaled by the music that would later be the S+ in thesound-versus-sound discrimination alternated with extinction sig-naled by silence In this group pretraining Pepi was observed bothpressing the button and taking pellets from the nipple but when sub-sequently isolated for melody discrimination sessions he consis-tently shied away from the nipple and again had to be dropped as asubject

The stimuli for the melody discrimination experiment (Figure 12)were all derived from the theme from Paganinirsquos 24th Caprice forsolo violin which is perhaps best known from Rachmaninoff rsquosldquoRhapsody on a Theme by Paganinirdquo S+ was the original melody asperformed on the MIDI keyboard S was derived from S+ by usingthe transformation described by Poli and Previde (1991) By using acomputer to modify the MIDI score S+rsquos order of pitches was re-versed whereas its original order of note durations was retained Inother words the first note of S got the duration of S+rsquos first notebut the pitch of S+rsquos last note the second note of S got the durationof S+rsquos second note but the pitch of S+rsquos next-to-last note and so onThis procedure can be thought of as retaining the rhythm track while

0

1

2

3S

lop

e (

ch

ang

ese

ssio

n)

1 2 3 4

Reversal Number

OroBeauty

Pepi

Figure 10 Experiment 2 (iterated reversals) improvementtrends For Beauty and Oro the improvement rate (Figure 9 re-gression line slopes percentage of nonresponse S trials per ses-sion) increases with each reversal

MUSIC DISCRIMINATIONS BY CARP 349

reversing the pitch track The result is two stimuli that are ldquoidenticalwith respect to their mean frequency note duration and rhythm butnoticeably different in their melodic patternsrdquo (Poli amp Previde 1991p 12) Such a pitch-track-reversed melody differs from a completelybackwards melody only in rhythm sacrificing the linkage betweeneach pitch and its original duration in order to preserve the originalsequence of durations per se (If the original melodymdashunlike the

Rachmaninoffmdashhas a palindromic rhythm track the pitch-track -reversed melody and the completely backwards melody are identical)The melodies were recorded using the same MIDI apparatus as thatdescribed above To enhance clarity the tempo was somewhat slowerthan that of the usual piano performance

Over the course of 53 sessions the instrumental timbre alternatedsix times between strings and acoustic piano but in any given ses-

0

25

50

75

100

Tri

als

wit

h N

o P

res

s

S+

ITI

S-

Beauty

0

25

50

75

100

Tri

als

wit

h N

o P

ress

S+

ITI

S-

Oro

Same Timbre Different Timbre Same Timbre

S+S-ITI

Pepi ceased responding

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 Session Number

S+

ITI

S-

Pepi

Figure 11 Experiment 3 (transition to MIDI and timbre study) percentages of S+ and S trials dur-ing which the fish did not press the button During the first 12 sessions the stimuli consisted of a singletrack from each of the two commercial recordings the subjects had last heard 10 months earlier at theconclusion of the iterated-reversal experiment the immediate resumption of accurate discrimination sug-gests long-term memory of training The circled data points (Sessions 13 and 24) indicate the introduc-tion of the first- and second-generation synthetic music From Session 47 until the end of the experimentS+ and S had identical timbre each boxed data point pair indicates the first presentation of a new tim-bre Session 47 rock piano Session 55 chiffloot and Session 62 guitar Crosses denote silence

350 CHASE

sion S+ and S always had the same timbre The discrimination pro-tocol was unchanged from the previous experiments except that thesession termination trigger was raised from 50 to 55 pellets As a pre-liminary test for a possible perceptual invariance (Hulse Takeuchi ampBraaten 1992) S+ was transposed down a fifth in Sessions 51ndash52

After 53 sessions it was discovered that the MIDI technology hadintroduced artifactual differences between S+ and S A musicallyattuned visitor to the lab detected minor variations in note durationsbetween the two stimuli which apparently had resulted from incor-rect handling of the attackndashsustainndashdecay envelopes of S+rsquos recordednotes There also turned out to be subtle volume differences whichwere said to have resulted from the combination of the MIDI scoreediting process and the volume compression function in the digitalaudio tape (DAT) recorder used to create stimulus master tapesThese differences were confirmed by careful examination of thewaveforms using a computer oscilloscope Therefore a second gen-eration of S was created by direct numerical substitution of the S+pitches into the MIDI score in reverse order and by recording a newmaster tape with all volume compression disabled The correctionswere verified by waveform analysis

After eight sessions with the second-generat ion S both S+ andS were shortened by the removal of each onersquos distinctive initial noteand seven sessions later they were further shortened by the removal oftheir remaining initial six and final four notes The purpose of thesestimulus contractions was to look for behavioral disruption that might

indicate that the subject had been discriminating the melodies on thebasis of such local features as the absolute pitch of the initial note

Results and DiscussionBeautyrsquos performance inexplicably deteriorated to the

point where he had to be dropped as a subjectFigures 13 and 14 report the performance of Oro the only

fish to complete the melody experiment The data showthat without timbre cues Oro clearly discriminated betweenthe two melodies [in each stimulus condition (ie second-generation S first-note-removed and both-ends-clipped)5 final sessions t(4) gt 10 p lt 001]

Oro responded more to S+ than to S even in the veryfirst session with melodic stimuli Familiarization with theS+ during pretraining could well have contributed to thisresponse bias perhaps partly because music heard in asound-versus-silence context had consistently become theS+ in a subsequent sound-versus-sound discriminationHowever the MIDI artifacts in the first-generation stim-uli might also have played a role

Session 54 in which the corrected S was introducedmarks a significant reduction of the separation between

Figure 12 Experiment 4 (melody discrimination) musical scores of the normal (S+) and pitch-reversed (S )melodies

MUSIC DISCRIMINATIONS BY CARP 351

the S+ and the S nonresponse percentages [two-tailed two-sample t test assuming unequal variances contrasting themean difference between S and S+ nonresponse per-centages before and after the change 8 observations just be-fore the stimulus change vs 8 observations just after t(11) =277 p lt 019] This implies that the rather subtle artifactsin the original S had indeed been exploited as discrimi-nants

One oddity is the fact that although the stimuli changedsignificantly in Sessions 54 (second-generation S ) and62 (removal of the first note of S+ and S ) in each case

a pronounced anomaly in Ororsquos performance occurred inthe following session

Studies of melody discrimination in animals have oftenfound that the behavior was controlled by local featuressuch as timbre pitch register or the absolute pitch of the ini-tial note rather than by the melodic patterning per se(DrsquoAmato amp Salmon 1984 Hulse amp Cynx 1985 Hulseamp Page 1988 Poli amp Previde 1991) (In this paper for theterm local properties I follow the convention of referringnot only to features like distinctive individual notes whichare clearly local in a temporal sense but also to features

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 70

Session Number

S+

S-

= Piano= Down a fifth= wo 1st note= wo 1st 7 amp last 4 notes

S+S-ITI

Figure 13 Experiment 4 (melody discrimination) trials with no responses The MIDI timbre was violin except for 13 sessions ofpiano as marked The corrected S was introduced at Session 54 The first notes of S+ and S were removed at Session 62 The sixinitial and four final notes were removed at Session 69 Crosses denote silence

Figure 14 Experiment 4 (melody discrimination) all responses Sessions terminated with the S+ trial in which the 55th pel-let was dispensed Crosses denote silence

0

20

40

60

All

Pre

sses

0 10 20 30 40 50 60 70

Session Number

S+

S-

Oro

S+S-ITI

352 CHASE

like timbre and pitch register which although recogniz-able in any local segment can be constant over the dura-tion of the stimulus and which therefore might arguablybe called global properties) It should not be surprisingthat with sequential stimuli such as sound animals oftenexploit local features in preference to global pattern fea-tures In the acoustic domain features that are instantly rec-ognizable presumably confer a survival advantage not onlyon listeners but also on creatures in whose interest it is tobe identifiable by sounds they make Oro did not have tim-bre available as a discriminant but there is no conclusiveevidence that he did or did not use other local features andit is not known which if any global features he might haveused

It warrants mention that in this type of discriminationexperiment inaccurate responding need not imply that thesubject is musically insensitive because musical sensitiv-ity can actually confound discriminative accuracy if bothstimuli are musically plausible or stylistically similar In-deed throughout this experiment the stimuli were moni-tored through a speaker in the laboratory office and S+ andS became so familiar and the pitch-track-reversed Ssounded so pleasing that human observers occasionallybecame confused as to which reinforcement contingencywas in force in the tank

The finding that Oro did not need timbre cues to dis-criminate melodies contrasts sharply with the result in ratsreported by Poli and Previde (1991) Using as stimuli for-ward and pitch-track-reversed versions of the melodyldquoFregravere Jacquesrdquo they tested for discrimination on the basisof melodic pattern The rats had neither previous experi-mental experience nor prior familiarity with music In anattempt to preclude the exploitation of local features suchas the absolute pitch of distinctively positioned notes each15-sec stimulus presentation began at a randomly chosenposition within the melody Different groups of subjectswere asked to discriminate two melodic stimuli that dif-fered in melody only in timbre only or in both attributesHowever the stimuli were never heard as unitary melodiesfrom start to finish and were presented in a continuousstream of randomly sequenced exposures with responsesin the presence of S+ being reinforced only on an FR-5schedule This would seem to be such a formidable task asto make it unsurprising that animals failed except when tim-bre a consistent property of every note in each stimuluswas available as a discriminant However Poli and Previdedid suggest that rats might well prove able to discriminatemelodies without timbre cues under other conditions

CONCLUDING REMARKS

The distinction between local features and pattern fea-tures although it arose in connection with melody dis-crimination is equally relevant to the categorization ex-periment To say that in classifying music as blues orclassical the koi might have been responding to deepgeneric attributes is not to say that they were necessarilyusing anything other than local cues because the diag-

nostic property could have been a particular combinationof timbre loudness pitch brief rhythmic or melodic fig-ures and other such local features A human scanning aradio dial requires only a fraction of a second to identifythe genre of a given station hardly enough time for patternfeatures to manifest themselves so a brief sample of musiccould well contain something recognizable to an animalthat had a rote store of auditory feature memories Localfeatures might control classification behavior even whenthere is extensive exposure to a stimulus Conceivably an-imals could acquire a functional understanding of musicentirely on the basis of the distribution and frequency ofvarious combinations of essentially local features with-out regard to the artistic pattern features in terms of whichmusical genres are commonly defined

Prior to this series of experiments the prevailing opinionappeared to be skepticism as to whether koi could dis-criminate one piece of music from another under any cir-cumstances Now it appears that these animals can discrim-inate polyphonic music discriminate melodic patternsand even classify music by artistic genre As far as I knowthese experiments presented the most complex auditorystimuli to which fish have ever been shown capable ofmaking sophisticated discriminative responses Howeverthere remains the task of elucidating the stimulus controlfunctions of the constituents of that complexity such aspattern features local features and simple properties of thestimulus as a whole The present work was intended as ex-ploratory rather than explanatory and the results clearly ex-tend the known envelope of auditory capabilities in fish

REFERENCES

Baron M R (1965) The stimulus stimulus control and generaliza-tion In D I Mostovsky (Ed) Stimulus generalization (pp 62-71)Stanford CA Stanford University Press

Chase A R amp Hill W (1999) Reliable operant apparatus for fishAudio stimulus generator response button and pellet-dispensing nip-ple Behavior Research Methods Instruments amp Computers 31 470-478

Coombs S Jannsen J amp Montgomery J C (1992) Functional andevolutionary implications of peripheral diversity in lateral line sys-tems In D B Webster R R Fay amp A N Popper (Eds) The evolu-tionary biology of hearing (pp 267-294) New York Springer-Verlag

DrsquoAmato M R amp Salmon D P (1982) Tune discrimination in mon-keys (Cebus apella) and rats Animal Learning amp Behavior 10 126-134

DrsquoAmato M R amp Salmon D P (1984) Processing of complex au-ditory stimuli (tunes) by rats and monkeys (Cebus apella) AnimalLearning amp Behavior 12 184-194

Fay R R (1988) Hearing in vertebrates A psychophysics data-bookWinnetka IL Hill-Fay Associates

Fay R R (1992) Analytic listening in goldfish Hearing Research 59101-107

Fay R R (1994) Perception of temporal acoustic patterns by the gold-fish (Carassius auratus) Hearing Research 76 158-172

Fay R R (1995) Perception of spectrally and temporally complexsounds by the goldfish (Carassius auratus) Hearing Research 89146-154

Fay R R (1998) Auditory stream segregation in goldfish (Carassiusauratus) Hearing Research 120 69-76

Fay R R amp Ream T J (1986) Acoustic response and tuning in sac-cular nerve fibers of the goldfish (Carassius auratus) Journal of theAcoustical Society of America 79 1883-1895

Hartman W M (1988) Pitch perception and the segregation and inte-

MUSIC DISCRIMINATIONS BY CARP 345

Just before the first reversal the stimuli had been a House of Bluescompilation (S+) and a baroque horn compilation (S ) When thecontingencies were reversed making blues S and classical S+both stimuli were also replaced The first reversal stimuli were Bachoboe concertos (S+) and John Lee Hookerrsquos Real Folks Blues (S )both very familiar to the fish In the next three phases of the first re-versal three additional pairs of familiar CDs were used In the fifthand final phase of the first reversal the fish were exposed to entirelynovel stimuli (S The Blues Story compilation S+ Bach triosonatas) As in the categorization study the first session with novelstimuli (Session 224) served as a probe testing for open-ended cat-egorization Blues and classical successively exchanged roles as S+and S in three additional reversal phases all using familiar stim-uli As can be seen in Figure 4 when the first and third reversals oc-curred at least one stimulus CD changed as well The final reversalbrought the contingencies back to where they had been before thefirst reversalmdashnamely with blues as S+ and classical as S

ResultsThe first reversal (Session 182) produced considerable

behavioral disruption and erroneous responding (see Fig-

ures 8 and 9) In the first 6ndash9 sessions the increase in re-sponding to the genre newly become S+ was insufficientfor any fish to earn 50 reinforcements within the 90-mintime limit (Figure 8) Beauty and Oro steadily improvedand were reliably discriminating by the 16th and 23rd ses-sions respectively Pepi achieved significance by Session 9but then his performance was substandard until Session 27[5 sessions ts(4) gt 229 p lt 010 p lt 009 and p lt 042respectively] Near the end of the first reversal the probesession (224) revealed that the classification behavior ex-hibited by Beauty and Oro was clearly open-ended catego-rization With each successive reversal it took fewer sessionsfor Beauty and Oro to demonstrate clear discrimination(Figures 9 and 10) Even Pepi eventually learned each re-versalmdashalbeit while continuing to call attention to the ex-istence of considerable and systematic individual differ-ences among fish In Figure 9 least-squares regressionlines are plotted for S nonresponse data and as is shownin Figure 10 their slopes indicate improvement rates of

0

50

100 Beauty

0

50

100 Oro

0

50

100

Mean 115 120 131 138 152 157 163 168 177 Mean

Probe Sessions (Novel CDs) Probes

Pepi

Non probes

S+S-ITI

Tri

als

wit

h N

o P

ress

Tri

als

wit

h N

o P

ress

Tri

als

wit

h N

o P

res

s

Figure 7 Experiment 1 (categorization) categorization performance during probe ses-sions (ie all-novel stimuli) percentages of S+ trials intertrial intervals (ITI) and S tri-als in which the fish did not respond Black bars indicate S+ gray bars indicate S andwhite bars indicate ITI Low nonresponse percentages for S+ indicate a high likelihoodof responding during S+ whereas high nonresponse percentages for S indicate that thefish tended to ignore the button during S The leftmost ldquoMeanrdquo bars show the averagesof all the nonprobe sessions in the session range 115ndash181 and the rightmost ldquoMeanrdquo barsshow the averages of the probe sessions

346 CHASE

08 and 11 per session for Beauty and Oro respec-tively during the first reversal (Sessions 182ndash238) Overthe final 5 sessions of each reversal phase discriminationby Beauty Oro and Pepi was statistically significant at

levels always better than p lt 010 p lt 016 and p lt 042respectively [ts(4) gt 229] It can be seen in Figure 8 thatwith each reversal the increase in responding to the new S+was generally faster than the extinction to the former S+

0

20

40

60

80

100

120

All

Pre

sses

Beauty

0

20

40

60

80

100

120

All

Pre

sses

Oro

ITI

Session Number

blues

classical classicalbluesblues

0

20

40

60

80

100

120

All

Pre

sses

150 175 200 225 250 275 300

Pepi

classical

BluesClassical

Figure 8 Experiment 2 (iterated reversals) counts of all responses by session Note that in graphs of reversal data the symbols con-sistently indicate genre (open squares blues filled triangles classical) not stimulus semantics (S+ or S ) which of course change ateach reversal This convention highlights the fluctuating response pattern associated with each genre longitudinally as successive re-versals of reinforcement contingency produce disruption and then learning with increasing efficiency The primary session termina-tion trigger was the trial on which the 50th pellet was delivered but in the early sessions of the first reversal no subject made as manyas 50 ldquocorrectrdquo responses to the former S within the session time limit even while responding many more than 50 times without re-inforcement to the former S+ Note that the extinction-induced response frenzy associated with a genrersquos suddenly becoming S de-creases with each reversal Crosses denote silence

MUSIC DISCRIMINATIONS BY CARP 347

EXPERIMENT 3Transition to Synthetic Keyboard Music and

Polyphonic Discrimination with Identical Timbre

The next step was to try to extend the learned classifi-cation of natural music to MIDI (Musical Instrument Dig-

ital Interface) synthesized music in which S+ and Swere not distinguishable by timbre

MethodPretraining After the iterated-reversal experiment the fish re-

mained in the homeexperimental tank from which all the appara-tus had been removed and they were not exposed to music or to anytraining or experimental procedures for a period of 10 months The

Tri

als

wit

h N

o P

ress

0

25

50

75

100

Reversals

Oro

classical

blues

classical

classical

blues

bluesTri

als

wit

h N

o P

ress

0

25

50

75

100

150 200 250 300

Session Number

Pepi

0

25

50

75

100

First Reversal

Beauty

Probe

Tri

als

wit

h N

o P

ress

ITI

BluesClassicalITI

Figure 9 Experiment 2 (iterated reversals) percentages of trials with no responses by session Note the increasingly efficient learn-ing of nonresponding to each former S+ as shown by the increasing slopes of the least-squares regression lines Session 224 (dashedline) was a probe the accurate discrimination of entirely novel stimuli indicates that the fish were performing open-ended catego-rization Crosses denote silence

348 CHASE

work resumed with a reintroduction to the apparatus and protocol asleft off at the end of the fourth and final reversalmdashthat is with S+and S being blues and classical respectively However the fishwere also being prepared to encounter the synthetic stimuli that werebeing created at that time which consisted of a single short piecefrom each genre rather than a collection comparable in duration andvariety with the commercial CDs used previously Therefore in pre-training the stimuli were the same two CDs the subjects had lastheard (see Figure 4 Session 300) but only a single track from eachS was an excerpt from a Bach oboe concerto S+ was the John LeeHooker song ldquoOne Bourbon One Scotch and One Beerrdquo of whicha synthesized version was in the works

Initially Beauty and Oro seemed to manifest effects of the longhiatus in the form of low response rates (not enough to earn 50 pel-lets in a session) and some transient difficulties operating the buttonand taking pellets from the nipple However even allowing for somerelearning and the reduced size of the new stimuli the immediacywith which all 3 subjects exhibited highly accurate discriminationsuggests that the original discrimination training had been retained(compare the leftmost sessions in Figure 11 with the rightmost inFigure 9)

Procedure The new stimuli were musically simplif ied MIDIkeyboard renditions of music of the types the f ish had alreadylearned to classify S+ was the familiar blues song described aboveand S was the unfamiliar Fugue 2 from Book I of Bachrsquos Well-Tempered Clavier To minimize the presence of extraneous cues allthe performances were done by the same musician with the sameequipment (a Kurzweil Model k2000vp keyboard Young Chang Re-search and Development Institute Waltham MA) the same se-quencing software (Studio Vision Pro Version 40 Opcode SystemsNashville TN) and the same settings for volume and for timbre(acoustic piano) Because the new stimuli were so short that theywould repeat after only a few trials rote memory could play a rolein their discrimination and thus the operative level of stimulus con-trol was being allowed to potentially regress from categorization todiscrimination

The initial synthetic stimuli turned out to trigger a deteriorationin classification accuracy (Figure 11 Session 13) It seemed possi-ble that this was an artifact of the musical translation process be-cause even humans had some difficulty recognizing the John LeeHooker song in synthetic form It had gone from bluesy to bouncyits original bass inflections were absent and there was no melodicvoice comparable with that of the singer Therefore at Session 24 Iintroduced a second generation of stimuli S+ remained the samepiece but the performance was somewhat more faithful to themodel The old S (the Bach fugue) had been much shorter than S+and thus had been repeating more often so it was replaced by a syn-

thesized rendition of the f irst movement of Vivaldirsquos ConcertoGrosso in A minor Opus 3 No 6 whose duration more closelymatched that of S+ In addition the timbre of the blues was changedfrom acoustic piano to rock piano thus adding timbre as an availablediscriminant However from Session 47 until the end of the experi-ment S+ and S again had timbre in common specifically rockpiano (starting in Session 47) chiffloot (starting in Session 55) andguitar (starting in Session 62)

ResultsWith the first presentations in a synthetic timbre discrim-

ination accuracy deteriorated (Figure 11 Sessions 13ndash23)perhaps because the first synthetic S+ was not a good enoughexemplar of the blues genre Pepi essentially ceased re-sponding during this time and had to be dropped from thestudy Starting at Session 24 with improved stimuli and adifference in timbre between S+ and S the behavior ofboth remaining subjects immediately changed and there-after their discriminative accuracy improved continually

When S+ and S were again made identical in timbre(Session 47) accurate classification persisted despite aperformance decrement probably related to the loss of asalient cue When the same pair of MIDI sequences waspresented in additional timbres generalization of accurateclassification to the new sounds appeared seamless The datafrom Session 47 and onward demonstrate [Sessions 18ts(17) gt 16 ps lt 001] that koi are capable of discriminat-ing polyphonic music on the basis of features other thanthe timbre of individual tone sources

EXPERIMENT 4 Discrimination of Melodies

Without Timbre Cues

After observing that instrumental timbre seemed not tobe a necessary discriminant in polyphonic music I inves-tigated whether timbre was necessary for koi to discrimi-nate single-voice musicmdashthat is melodies

MethodIn order to familiarize the subjects with the S+ melody and also

in hopes of rehabilitating Pepi this experiment began with severalsessions of collective exposure to a sound-versus-silence contin-gency CRF signaled by the music that would later be the S+ in thesound-versus-sound discrimination alternated with extinction sig-naled by silence In this group pretraining Pepi was observed bothpressing the button and taking pellets from the nipple but when sub-sequently isolated for melody discrimination sessions he consis-tently shied away from the nipple and again had to be dropped as asubject

The stimuli for the melody discrimination experiment (Figure 12)were all derived from the theme from Paganinirsquos 24th Caprice forsolo violin which is perhaps best known from Rachmaninoff rsquosldquoRhapsody on a Theme by Paganinirdquo S+ was the original melody asperformed on the MIDI keyboard S was derived from S+ by usingthe transformation described by Poli and Previde (1991) By using acomputer to modify the MIDI score S+rsquos order of pitches was re-versed whereas its original order of note durations was retained Inother words the first note of S got the duration of S+rsquos first notebut the pitch of S+rsquos last note the second note of S got the durationof S+rsquos second note but the pitch of S+rsquos next-to-last note and so onThis procedure can be thought of as retaining the rhythm track while

0

1

2

3S

lop

e (

ch

ang

ese

ssio

n)

1 2 3 4

Reversal Number

OroBeauty

Pepi

Figure 10 Experiment 2 (iterated reversals) improvementtrends For Beauty and Oro the improvement rate (Figure 9 re-gression line slopes percentage of nonresponse S trials per ses-sion) increases with each reversal

MUSIC DISCRIMINATIONS BY CARP 349

reversing the pitch track The result is two stimuli that are ldquoidenticalwith respect to their mean frequency note duration and rhythm butnoticeably different in their melodic patternsrdquo (Poli amp Previde 1991p 12) Such a pitch-track-reversed melody differs from a completelybackwards melody only in rhythm sacrificing the linkage betweeneach pitch and its original duration in order to preserve the originalsequence of durations per se (If the original melodymdashunlike the

Rachmaninoffmdashhas a palindromic rhythm track the pitch-track -reversed melody and the completely backwards melody are identical)The melodies were recorded using the same MIDI apparatus as thatdescribed above To enhance clarity the tempo was somewhat slowerthan that of the usual piano performance

Over the course of 53 sessions the instrumental timbre alternatedsix times between strings and acoustic piano but in any given ses-

0

25

50

75

100

Tri

als

wit

h N

o P

res

s

S+

ITI

S-

Beauty

0

25

50

75

100

Tri

als

wit

h N

o P

ress

S+

ITI

S-

Oro

Same Timbre Different Timbre Same Timbre

S+S-ITI

Pepi ceased responding

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 Session Number

S+

ITI

S-

Pepi

Figure 11 Experiment 3 (transition to MIDI and timbre study) percentages of S+ and S trials dur-ing which the fish did not press the button During the first 12 sessions the stimuli consisted of a singletrack from each of the two commercial recordings the subjects had last heard 10 months earlier at theconclusion of the iterated-reversal experiment the immediate resumption of accurate discrimination sug-gests long-term memory of training The circled data points (Sessions 13 and 24) indicate the introduc-tion of the first- and second-generation synthetic music From Session 47 until the end of the experimentS+ and S had identical timbre each boxed data point pair indicates the first presentation of a new tim-bre Session 47 rock piano Session 55 chiffloot and Session 62 guitar Crosses denote silence

350 CHASE

sion S+ and S always had the same timbre The discrimination pro-tocol was unchanged from the previous experiments except that thesession termination trigger was raised from 50 to 55 pellets As a pre-liminary test for a possible perceptual invariance (Hulse Takeuchi ampBraaten 1992) S+ was transposed down a fifth in Sessions 51ndash52

After 53 sessions it was discovered that the MIDI technology hadintroduced artifactual differences between S+ and S A musicallyattuned visitor to the lab detected minor variations in note durationsbetween the two stimuli which apparently had resulted from incor-rect handling of the attackndashsustainndashdecay envelopes of S+rsquos recordednotes There also turned out to be subtle volume differences whichwere said to have resulted from the combination of the MIDI scoreediting process and the volume compression function in the digitalaudio tape (DAT) recorder used to create stimulus master tapesThese differences were confirmed by careful examination of thewaveforms using a computer oscilloscope Therefore a second gen-eration of S was created by direct numerical substitution of the S+pitches into the MIDI score in reverse order and by recording a newmaster tape with all volume compression disabled The correctionswere verified by waveform analysis

After eight sessions with the second-generat ion S both S+ andS were shortened by the removal of each onersquos distinctive initial noteand seven sessions later they were further shortened by the removal oftheir remaining initial six and final four notes The purpose of thesestimulus contractions was to look for behavioral disruption that might

indicate that the subject had been discriminating the melodies on thebasis of such local features as the absolute pitch of the initial note

Results and DiscussionBeautyrsquos performance inexplicably deteriorated to the

point where he had to be dropped as a subjectFigures 13 and 14 report the performance of Oro the only

fish to complete the melody experiment The data showthat without timbre cues Oro clearly discriminated betweenthe two melodies [in each stimulus condition (ie second-generation S first-note-removed and both-ends-clipped)5 final sessions t(4) gt 10 p lt 001]

Oro responded more to S+ than to S even in the veryfirst session with melodic stimuli Familiarization with theS+ during pretraining could well have contributed to thisresponse bias perhaps partly because music heard in asound-versus-silence context had consistently become theS+ in a subsequent sound-versus-sound discriminationHowever the MIDI artifacts in the first-generation stim-uli might also have played a role

Session 54 in which the corrected S was introducedmarks a significant reduction of the separation between

Figure 12 Experiment 4 (melody discrimination) musical scores of the normal (S+) and pitch-reversed (S )melodies

MUSIC DISCRIMINATIONS BY CARP 351

the S+ and the S nonresponse percentages [two-tailed two-sample t test assuming unequal variances contrasting themean difference between S and S+ nonresponse per-centages before and after the change 8 observations just be-fore the stimulus change vs 8 observations just after t(11) =277 p lt 019] This implies that the rather subtle artifactsin the original S had indeed been exploited as discrimi-nants

One oddity is the fact that although the stimuli changedsignificantly in Sessions 54 (second-generation S ) and62 (removal of the first note of S+ and S ) in each case

a pronounced anomaly in Ororsquos performance occurred inthe following session

Studies of melody discrimination in animals have oftenfound that the behavior was controlled by local featuressuch as timbre pitch register or the absolute pitch of the ini-tial note rather than by the melodic patterning per se(DrsquoAmato amp Salmon 1984 Hulse amp Cynx 1985 Hulseamp Page 1988 Poli amp Previde 1991) (In this paper for theterm local properties I follow the convention of referringnot only to features like distinctive individual notes whichare clearly local in a temporal sense but also to features

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 70

Session Number

S+

S-

= Piano= Down a fifth= wo 1st note= wo 1st 7 amp last 4 notes

S+S-ITI

Figure 13 Experiment 4 (melody discrimination) trials with no responses The MIDI timbre was violin except for 13 sessions ofpiano as marked The corrected S was introduced at Session 54 The first notes of S+ and S were removed at Session 62 The sixinitial and four final notes were removed at Session 69 Crosses denote silence

Figure 14 Experiment 4 (melody discrimination) all responses Sessions terminated with the S+ trial in which the 55th pel-let was dispensed Crosses denote silence

0

20

40

60

All

Pre

sses

0 10 20 30 40 50 60 70

Session Number

S+

S-

Oro

S+S-ITI

352 CHASE

like timbre and pitch register which although recogniz-able in any local segment can be constant over the dura-tion of the stimulus and which therefore might arguablybe called global properties) It should not be surprisingthat with sequential stimuli such as sound animals oftenexploit local features in preference to global pattern fea-tures In the acoustic domain features that are instantly rec-ognizable presumably confer a survival advantage not onlyon listeners but also on creatures in whose interest it is tobe identifiable by sounds they make Oro did not have tim-bre available as a discriminant but there is no conclusiveevidence that he did or did not use other local features andit is not known which if any global features he might haveused

It warrants mention that in this type of discriminationexperiment inaccurate responding need not imply that thesubject is musically insensitive because musical sensitiv-ity can actually confound discriminative accuracy if bothstimuli are musically plausible or stylistically similar In-deed throughout this experiment the stimuli were moni-tored through a speaker in the laboratory office and S+ andS became so familiar and the pitch-track-reversed Ssounded so pleasing that human observers occasionallybecame confused as to which reinforcement contingencywas in force in the tank

The finding that Oro did not need timbre cues to dis-criminate melodies contrasts sharply with the result in ratsreported by Poli and Previde (1991) Using as stimuli for-ward and pitch-track-reversed versions of the melodyldquoFregravere Jacquesrdquo they tested for discrimination on the basisof melodic pattern The rats had neither previous experi-mental experience nor prior familiarity with music In anattempt to preclude the exploitation of local features suchas the absolute pitch of distinctively positioned notes each15-sec stimulus presentation began at a randomly chosenposition within the melody Different groups of subjectswere asked to discriminate two melodic stimuli that dif-fered in melody only in timbre only or in both attributesHowever the stimuli were never heard as unitary melodiesfrom start to finish and were presented in a continuousstream of randomly sequenced exposures with responsesin the presence of S+ being reinforced only on an FR-5schedule This would seem to be such a formidable task asto make it unsurprising that animals failed except when tim-bre a consistent property of every note in each stimuluswas available as a discriminant However Poli and Previdedid suggest that rats might well prove able to discriminatemelodies without timbre cues under other conditions

CONCLUDING REMARKS

The distinction between local features and pattern fea-tures although it arose in connection with melody dis-crimination is equally relevant to the categorization ex-periment To say that in classifying music as blues orclassical the koi might have been responding to deepgeneric attributes is not to say that they were necessarilyusing anything other than local cues because the diag-

nostic property could have been a particular combinationof timbre loudness pitch brief rhythmic or melodic fig-ures and other such local features A human scanning aradio dial requires only a fraction of a second to identifythe genre of a given station hardly enough time for patternfeatures to manifest themselves so a brief sample of musiccould well contain something recognizable to an animalthat had a rote store of auditory feature memories Localfeatures might control classification behavior even whenthere is extensive exposure to a stimulus Conceivably an-imals could acquire a functional understanding of musicentirely on the basis of the distribution and frequency ofvarious combinations of essentially local features with-out regard to the artistic pattern features in terms of whichmusical genres are commonly defined

Prior to this series of experiments the prevailing opinionappeared to be skepticism as to whether koi could dis-criminate one piece of music from another under any cir-cumstances Now it appears that these animals can discrim-inate polyphonic music discriminate melodic patternsand even classify music by artistic genre As far as I knowthese experiments presented the most complex auditorystimuli to which fish have ever been shown capable ofmaking sophisticated discriminative responses Howeverthere remains the task of elucidating the stimulus controlfunctions of the constituents of that complexity such aspattern features local features and simple properties of thestimulus as a whole The present work was intended as ex-ploratory rather than explanatory and the results clearly ex-tend the known envelope of auditory capabilities in fish

REFERENCES

Baron M R (1965) The stimulus stimulus control and generaliza-tion In D I Mostovsky (Ed) Stimulus generalization (pp 62-71)Stanford CA Stanford University Press

Chase A R amp Hill W (1999) Reliable operant apparatus for fishAudio stimulus generator response button and pellet-dispensing nip-ple Behavior Research Methods Instruments amp Computers 31 470-478

Coombs S Jannsen J amp Montgomery J C (1992) Functional andevolutionary implications of peripheral diversity in lateral line sys-tems In D B Webster R R Fay amp A N Popper (Eds) The evolu-tionary biology of hearing (pp 267-294) New York Springer-Verlag

DrsquoAmato M R amp Salmon D P (1982) Tune discrimination in mon-keys (Cebus apella) and rats Animal Learning amp Behavior 10 126-134

DrsquoAmato M R amp Salmon D P (1984) Processing of complex au-ditory stimuli (tunes) by rats and monkeys (Cebus apella) AnimalLearning amp Behavior 12 184-194

Fay R R (1988) Hearing in vertebrates A psychophysics data-bookWinnetka IL Hill-Fay Associates

Fay R R (1992) Analytic listening in goldfish Hearing Research 59101-107

Fay R R (1994) Perception of temporal acoustic patterns by the gold-fish (Carassius auratus) Hearing Research 76 158-172

Fay R R (1995) Perception of spectrally and temporally complexsounds by the goldfish (Carassius auratus) Hearing Research 89146-154

Fay R R (1998) Auditory stream segregation in goldfish (Carassiusauratus) Hearing Research 120 69-76

Fay R R amp Ream T J (1986) Acoustic response and tuning in sac-cular nerve fibers of the goldfish (Carassius auratus) Journal of theAcoustical Society of America 79 1883-1895

Hartman W M (1988) Pitch perception and the segregation and inte-

346 CHASE

08 and 11 per session for Beauty and Oro respec-tively during the first reversal (Sessions 182ndash238) Overthe final 5 sessions of each reversal phase discriminationby Beauty Oro and Pepi was statistically significant at

levels always better than p lt 010 p lt 016 and p lt 042respectively [ts(4) gt 229] It can be seen in Figure 8 thatwith each reversal the increase in responding to the new S+was generally faster than the extinction to the former S+

0

20

40

60

80

100

120

All

Pre

sses

Beauty

0

20

40

60

80

100

120

All

Pre

sses

Oro

ITI

Session Number

blues

classical classicalbluesblues

0

20

40

60

80

100

120

All

Pre

sses

150 175 200 225 250 275 300

Pepi

classical

BluesClassical

Figure 8 Experiment 2 (iterated reversals) counts of all responses by session Note that in graphs of reversal data the symbols con-sistently indicate genre (open squares blues filled triangles classical) not stimulus semantics (S+ or S ) which of course change ateach reversal This convention highlights the fluctuating response pattern associated with each genre longitudinally as successive re-versals of reinforcement contingency produce disruption and then learning with increasing efficiency The primary session termina-tion trigger was the trial on which the 50th pellet was delivered but in the early sessions of the first reversal no subject made as manyas 50 ldquocorrectrdquo responses to the former S within the session time limit even while responding many more than 50 times without re-inforcement to the former S+ Note that the extinction-induced response frenzy associated with a genrersquos suddenly becoming S de-creases with each reversal Crosses denote silence

MUSIC DISCRIMINATIONS BY CARP 347

EXPERIMENT 3Transition to Synthetic Keyboard Music and

Polyphonic Discrimination with Identical Timbre

The next step was to try to extend the learned classifi-cation of natural music to MIDI (Musical Instrument Dig-

ital Interface) synthesized music in which S+ and Swere not distinguishable by timbre

MethodPretraining After the iterated-reversal experiment the fish re-

mained in the homeexperimental tank from which all the appara-tus had been removed and they were not exposed to music or to anytraining or experimental procedures for a period of 10 months The

Tri

als

wit

h N

o P

ress

0

25

50

75

100

Reversals

Oro

classical

blues

classical

classical

blues

bluesTri

als

wit

h N

o P

ress

0

25

50

75

100

150 200 250 300

Session Number

Pepi

0

25

50

75

100

First Reversal

Beauty

Probe

Tri

als

wit

h N

o P

ress

ITI

BluesClassicalITI

Figure 9 Experiment 2 (iterated reversals) percentages of trials with no responses by session Note the increasingly efficient learn-ing of nonresponding to each former S+ as shown by the increasing slopes of the least-squares regression lines Session 224 (dashedline) was a probe the accurate discrimination of entirely novel stimuli indicates that the fish were performing open-ended catego-rization Crosses denote silence

348 CHASE

work resumed with a reintroduction to the apparatus and protocol asleft off at the end of the fourth and final reversalmdashthat is with S+and S being blues and classical respectively However the fishwere also being prepared to encounter the synthetic stimuli that werebeing created at that time which consisted of a single short piecefrom each genre rather than a collection comparable in duration andvariety with the commercial CDs used previously Therefore in pre-training the stimuli were the same two CDs the subjects had lastheard (see Figure 4 Session 300) but only a single track from eachS was an excerpt from a Bach oboe concerto S+ was the John LeeHooker song ldquoOne Bourbon One Scotch and One Beerrdquo of whicha synthesized version was in the works

Initially Beauty and Oro seemed to manifest effects of the longhiatus in the form of low response rates (not enough to earn 50 pel-lets in a session) and some transient difficulties operating the buttonand taking pellets from the nipple However even allowing for somerelearning and the reduced size of the new stimuli the immediacywith which all 3 subjects exhibited highly accurate discriminationsuggests that the original discrimination training had been retained(compare the leftmost sessions in Figure 11 with the rightmost inFigure 9)

Procedure The new stimuli were musically simplif ied MIDIkeyboard renditions of music of the types the f ish had alreadylearned to classify S+ was the familiar blues song described aboveand S was the unfamiliar Fugue 2 from Book I of Bachrsquos Well-Tempered Clavier To minimize the presence of extraneous cues allthe performances were done by the same musician with the sameequipment (a Kurzweil Model k2000vp keyboard Young Chang Re-search and Development Institute Waltham MA) the same se-quencing software (Studio Vision Pro Version 40 Opcode SystemsNashville TN) and the same settings for volume and for timbre(acoustic piano) Because the new stimuli were so short that theywould repeat after only a few trials rote memory could play a rolein their discrimination and thus the operative level of stimulus con-trol was being allowed to potentially regress from categorization todiscrimination

The initial synthetic stimuli turned out to trigger a deteriorationin classification accuracy (Figure 11 Session 13) It seemed possi-ble that this was an artifact of the musical translation process be-cause even humans had some difficulty recognizing the John LeeHooker song in synthetic form It had gone from bluesy to bouncyits original bass inflections were absent and there was no melodicvoice comparable with that of the singer Therefore at Session 24 Iintroduced a second generation of stimuli S+ remained the samepiece but the performance was somewhat more faithful to themodel The old S (the Bach fugue) had been much shorter than S+and thus had been repeating more often so it was replaced by a syn-

thesized rendition of the f irst movement of Vivaldirsquos ConcertoGrosso in A minor Opus 3 No 6 whose duration more closelymatched that of S+ In addition the timbre of the blues was changedfrom acoustic piano to rock piano thus adding timbre as an availablediscriminant However from Session 47 until the end of the experi-ment S+ and S again had timbre in common specifically rockpiano (starting in Session 47) chiffloot (starting in Session 55) andguitar (starting in Session 62)

ResultsWith the first presentations in a synthetic timbre discrim-

ination accuracy deteriorated (Figure 11 Sessions 13ndash23)perhaps because the first synthetic S+ was not a good enoughexemplar of the blues genre Pepi essentially ceased re-sponding during this time and had to be dropped from thestudy Starting at Session 24 with improved stimuli and adifference in timbre between S+ and S the behavior ofboth remaining subjects immediately changed and there-after their discriminative accuracy improved continually

When S+ and S were again made identical in timbre(Session 47) accurate classification persisted despite aperformance decrement probably related to the loss of asalient cue When the same pair of MIDI sequences waspresented in additional timbres generalization of accurateclassification to the new sounds appeared seamless The datafrom Session 47 and onward demonstrate [Sessions 18ts(17) gt 16 ps lt 001] that koi are capable of discriminat-ing polyphonic music on the basis of features other thanthe timbre of individual tone sources

EXPERIMENT 4 Discrimination of Melodies

Without Timbre Cues

After observing that instrumental timbre seemed not tobe a necessary discriminant in polyphonic music I inves-tigated whether timbre was necessary for koi to discrimi-nate single-voice musicmdashthat is melodies

MethodIn order to familiarize the subjects with the S+ melody and also

in hopes of rehabilitating Pepi this experiment began with severalsessions of collective exposure to a sound-versus-silence contin-gency CRF signaled by the music that would later be the S+ in thesound-versus-sound discrimination alternated with extinction sig-naled by silence In this group pretraining Pepi was observed bothpressing the button and taking pellets from the nipple but when sub-sequently isolated for melody discrimination sessions he consis-tently shied away from the nipple and again had to be dropped as asubject

The stimuli for the melody discrimination experiment (Figure 12)were all derived from the theme from Paganinirsquos 24th Caprice forsolo violin which is perhaps best known from Rachmaninoff rsquosldquoRhapsody on a Theme by Paganinirdquo S+ was the original melody asperformed on the MIDI keyboard S was derived from S+ by usingthe transformation described by Poli and Previde (1991) By using acomputer to modify the MIDI score S+rsquos order of pitches was re-versed whereas its original order of note durations was retained Inother words the first note of S got the duration of S+rsquos first notebut the pitch of S+rsquos last note the second note of S got the durationof S+rsquos second note but the pitch of S+rsquos next-to-last note and so onThis procedure can be thought of as retaining the rhythm track while

0

1

2

3S

lop

e (

ch

ang

ese

ssio

n)

1 2 3 4

Reversal Number

OroBeauty

Pepi

Figure 10 Experiment 2 (iterated reversals) improvementtrends For Beauty and Oro the improvement rate (Figure 9 re-gression line slopes percentage of nonresponse S trials per ses-sion) increases with each reversal

MUSIC DISCRIMINATIONS BY CARP 349

reversing the pitch track The result is two stimuli that are ldquoidenticalwith respect to their mean frequency note duration and rhythm butnoticeably different in their melodic patternsrdquo (Poli amp Previde 1991p 12) Such a pitch-track-reversed melody differs from a completelybackwards melody only in rhythm sacrificing the linkage betweeneach pitch and its original duration in order to preserve the originalsequence of durations per se (If the original melodymdashunlike the

Rachmaninoffmdashhas a palindromic rhythm track the pitch-track -reversed melody and the completely backwards melody are identical)The melodies were recorded using the same MIDI apparatus as thatdescribed above To enhance clarity the tempo was somewhat slowerthan that of the usual piano performance

Over the course of 53 sessions the instrumental timbre alternatedsix times between strings and acoustic piano but in any given ses-

0

25

50

75

100

Tri

als

wit

h N

o P

res

s

S+

ITI

S-

Beauty

0

25

50

75

100

Tri

als

wit

h N

o P

ress

S+

ITI

S-

Oro

Same Timbre Different Timbre Same Timbre

S+S-ITI

Pepi ceased responding

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 Session Number

S+

ITI

S-

Pepi

Figure 11 Experiment 3 (transition to MIDI and timbre study) percentages of S+ and S trials dur-ing which the fish did not press the button During the first 12 sessions the stimuli consisted of a singletrack from each of the two commercial recordings the subjects had last heard 10 months earlier at theconclusion of the iterated-reversal experiment the immediate resumption of accurate discrimination sug-gests long-term memory of training The circled data points (Sessions 13 and 24) indicate the introduc-tion of the first- and second-generation synthetic music From Session 47 until the end of the experimentS+ and S had identical timbre each boxed data point pair indicates the first presentation of a new tim-bre Session 47 rock piano Session 55 chiffloot and Session 62 guitar Crosses denote silence

350 CHASE

sion S+ and S always had the same timbre The discrimination pro-tocol was unchanged from the previous experiments except that thesession termination trigger was raised from 50 to 55 pellets As a pre-liminary test for a possible perceptual invariance (Hulse Takeuchi ampBraaten 1992) S+ was transposed down a fifth in Sessions 51ndash52

After 53 sessions it was discovered that the MIDI technology hadintroduced artifactual differences between S+ and S A musicallyattuned visitor to the lab detected minor variations in note durationsbetween the two stimuli which apparently had resulted from incor-rect handling of the attackndashsustainndashdecay envelopes of S+rsquos recordednotes There also turned out to be subtle volume differences whichwere said to have resulted from the combination of the MIDI scoreediting process and the volume compression function in the digitalaudio tape (DAT) recorder used to create stimulus master tapesThese differences were confirmed by careful examination of thewaveforms using a computer oscilloscope Therefore a second gen-eration of S was created by direct numerical substitution of the S+pitches into the MIDI score in reverse order and by recording a newmaster tape with all volume compression disabled The correctionswere verified by waveform analysis

After eight sessions with the second-generat ion S both S+ andS were shortened by the removal of each onersquos distinctive initial noteand seven sessions later they were further shortened by the removal oftheir remaining initial six and final four notes The purpose of thesestimulus contractions was to look for behavioral disruption that might

indicate that the subject had been discriminating the melodies on thebasis of such local features as the absolute pitch of the initial note

Results and DiscussionBeautyrsquos performance inexplicably deteriorated to the

point where he had to be dropped as a subjectFigures 13 and 14 report the performance of Oro the only

fish to complete the melody experiment The data showthat without timbre cues Oro clearly discriminated betweenthe two melodies [in each stimulus condition (ie second-generation S first-note-removed and both-ends-clipped)5 final sessions t(4) gt 10 p lt 001]

Oro responded more to S+ than to S even in the veryfirst session with melodic stimuli Familiarization with theS+ during pretraining could well have contributed to thisresponse bias perhaps partly because music heard in asound-versus-silence context had consistently become theS+ in a subsequent sound-versus-sound discriminationHowever the MIDI artifacts in the first-generation stim-uli might also have played a role

Session 54 in which the corrected S was introducedmarks a significant reduction of the separation between

Figure 12 Experiment 4 (melody discrimination) musical scores of the normal (S+) and pitch-reversed (S )melodies

MUSIC DISCRIMINATIONS BY CARP 351

the S+ and the S nonresponse percentages [two-tailed two-sample t test assuming unequal variances contrasting themean difference between S and S+ nonresponse per-centages before and after the change 8 observations just be-fore the stimulus change vs 8 observations just after t(11) =277 p lt 019] This implies that the rather subtle artifactsin the original S had indeed been exploited as discrimi-nants

One oddity is the fact that although the stimuli changedsignificantly in Sessions 54 (second-generation S ) and62 (removal of the first note of S+ and S ) in each case

a pronounced anomaly in Ororsquos performance occurred inthe following session

Studies of melody discrimination in animals have oftenfound that the behavior was controlled by local featuressuch as timbre pitch register or the absolute pitch of the ini-tial note rather than by the melodic patterning per se(DrsquoAmato amp Salmon 1984 Hulse amp Cynx 1985 Hulseamp Page 1988 Poli amp Previde 1991) (In this paper for theterm local properties I follow the convention of referringnot only to features like distinctive individual notes whichare clearly local in a temporal sense but also to features

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 70

Session Number

S+

S-

= Piano= Down a fifth= wo 1st note= wo 1st 7 amp last 4 notes

S+S-ITI

Figure 13 Experiment 4 (melody discrimination) trials with no responses The MIDI timbre was violin except for 13 sessions ofpiano as marked The corrected S was introduced at Session 54 The first notes of S+ and S were removed at Session 62 The sixinitial and four final notes were removed at Session 69 Crosses denote silence

Figure 14 Experiment 4 (melody discrimination) all responses Sessions terminated with the S+ trial in which the 55th pel-let was dispensed Crosses denote silence

0

20

40

60

All

Pre

sses

0 10 20 30 40 50 60 70

Session Number

S+

S-

Oro

S+S-ITI

352 CHASE

like timbre and pitch register which although recogniz-able in any local segment can be constant over the dura-tion of the stimulus and which therefore might arguablybe called global properties) It should not be surprisingthat with sequential stimuli such as sound animals oftenexploit local features in preference to global pattern fea-tures In the acoustic domain features that are instantly rec-ognizable presumably confer a survival advantage not onlyon listeners but also on creatures in whose interest it is tobe identifiable by sounds they make Oro did not have tim-bre available as a discriminant but there is no conclusiveevidence that he did or did not use other local features andit is not known which if any global features he might haveused

It warrants mention that in this type of discriminationexperiment inaccurate responding need not imply that thesubject is musically insensitive because musical sensitiv-ity can actually confound discriminative accuracy if bothstimuli are musically plausible or stylistically similar In-deed throughout this experiment the stimuli were moni-tored through a speaker in the laboratory office and S+ andS became so familiar and the pitch-track-reversed Ssounded so pleasing that human observers occasionallybecame confused as to which reinforcement contingencywas in force in the tank

The finding that Oro did not need timbre cues to dis-criminate melodies contrasts sharply with the result in ratsreported by Poli and Previde (1991) Using as stimuli for-ward and pitch-track-reversed versions of the melodyldquoFregravere Jacquesrdquo they tested for discrimination on the basisof melodic pattern The rats had neither previous experi-mental experience nor prior familiarity with music In anattempt to preclude the exploitation of local features suchas the absolute pitch of distinctively positioned notes each15-sec stimulus presentation began at a randomly chosenposition within the melody Different groups of subjectswere asked to discriminate two melodic stimuli that dif-fered in melody only in timbre only or in both attributesHowever the stimuli were never heard as unitary melodiesfrom start to finish and were presented in a continuousstream of randomly sequenced exposures with responsesin the presence of S+ being reinforced only on an FR-5schedule This would seem to be such a formidable task asto make it unsurprising that animals failed except when tim-bre a consistent property of every note in each stimuluswas available as a discriminant However Poli and Previdedid suggest that rats might well prove able to discriminatemelodies without timbre cues under other conditions

CONCLUDING REMARKS

The distinction between local features and pattern fea-tures although it arose in connection with melody dis-crimination is equally relevant to the categorization ex-periment To say that in classifying music as blues orclassical the koi might have been responding to deepgeneric attributes is not to say that they were necessarilyusing anything other than local cues because the diag-

nostic property could have been a particular combinationof timbre loudness pitch brief rhythmic or melodic fig-ures and other such local features A human scanning aradio dial requires only a fraction of a second to identifythe genre of a given station hardly enough time for patternfeatures to manifest themselves so a brief sample of musiccould well contain something recognizable to an animalthat had a rote store of auditory feature memories Localfeatures might control classification behavior even whenthere is extensive exposure to a stimulus Conceivably an-imals could acquire a functional understanding of musicentirely on the basis of the distribution and frequency ofvarious combinations of essentially local features with-out regard to the artistic pattern features in terms of whichmusical genres are commonly defined

Prior to this series of experiments the prevailing opinionappeared to be skepticism as to whether koi could dis-criminate one piece of music from another under any cir-cumstances Now it appears that these animals can discrim-inate polyphonic music discriminate melodic patternsand even classify music by artistic genre As far as I knowthese experiments presented the most complex auditorystimuli to which fish have ever been shown capable ofmaking sophisticated discriminative responses Howeverthere remains the task of elucidating the stimulus controlfunctions of the constituents of that complexity such aspattern features local features and simple properties of thestimulus as a whole The present work was intended as ex-ploratory rather than explanatory and the results clearly ex-tend the known envelope of auditory capabilities in fish

REFERENCES

Baron M R (1965) The stimulus stimulus control and generaliza-tion In D I Mostovsky (Ed) Stimulus generalization (pp 62-71)Stanford CA Stanford University Press

Chase A R amp Hill W (1999) Reliable operant apparatus for fishAudio stimulus generator response button and pellet-dispensing nip-ple Behavior Research Methods Instruments amp Computers 31 470-478

Coombs S Jannsen J amp Montgomery J C (1992) Functional andevolutionary implications of peripheral diversity in lateral line sys-tems In D B Webster R R Fay amp A N Popper (Eds) The evolu-tionary biology of hearing (pp 267-294) New York Springer-Verlag

DrsquoAmato M R amp Salmon D P (1982) Tune discrimination in mon-keys (Cebus apella) and rats Animal Learning amp Behavior 10 126-134

DrsquoAmato M R amp Salmon D P (1984) Processing of complex au-ditory stimuli (tunes) by rats and monkeys (Cebus apella) AnimalLearning amp Behavior 12 184-194

Fay R R (1988) Hearing in vertebrates A psychophysics data-bookWinnetka IL Hill-Fay Associates

Fay R R (1992) Analytic listening in goldfish Hearing Research 59101-107

Fay R R (1994) Perception of temporal acoustic patterns by the gold-fish (Carassius auratus) Hearing Research 76 158-172

Fay R R (1995) Perception of spectrally and temporally complexsounds by the goldfish (Carassius auratus) Hearing Research 89146-154

Fay R R (1998) Auditory stream segregation in goldfish (Carassiusauratus) Hearing Research 120 69-76

Fay R R amp Ream T J (1986) Acoustic response and tuning in sac-cular nerve fibers of the goldfish (Carassius auratus) Journal of theAcoustical Society of America 79 1883-1895

Hartman W M (1988) Pitch perception and the segregation and inte-

MUSIC DISCRIMINATIONS BY CARP 347

EXPERIMENT 3Transition to Synthetic Keyboard Music and

Polyphonic Discrimination with Identical Timbre

The next step was to try to extend the learned classifi-cation of natural music to MIDI (Musical Instrument Dig-

ital Interface) synthesized music in which S+ and Swere not distinguishable by timbre

MethodPretraining After the iterated-reversal experiment the fish re-

mained in the homeexperimental tank from which all the appara-tus had been removed and they were not exposed to music or to anytraining or experimental procedures for a period of 10 months The

Tri

als

wit

h N

o P

ress

0

25

50

75

100

Reversals

Oro

classical

blues

classical

classical

blues

bluesTri

als

wit

h N

o P

ress

0

25

50

75

100

150 200 250 300

Session Number

Pepi

0

25

50

75

100

First Reversal

Beauty

Probe

Tri

als

wit

h N

o P

ress

ITI

BluesClassicalITI

Figure 9 Experiment 2 (iterated reversals) percentages of trials with no responses by session Note the increasingly efficient learn-ing of nonresponding to each former S+ as shown by the increasing slopes of the least-squares regression lines Session 224 (dashedline) was a probe the accurate discrimination of entirely novel stimuli indicates that the fish were performing open-ended catego-rization Crosses denote silence

348 CHASE

work resumed with a reintroduction to the apparatus and protocol asleft off at the end of the fourth and final reversalmdashthat is with S+and S being blues and classical respectively However the fishwere also being prepared to encounter the synthetic stimuli that werebeing created at that time which consisted of a single short piecefrom each genre rather than a collection comparable in duration andvariety with the commercial CDs used previously Therefore in pre-training the stimuli were the same two CDs the subjects had lastheard (see Figure 4 Session 300) but only a single track from eachS was an excerpt from a Bach oboe concerto S+ was the John LeeHooker song ldquoOne Bourbon One Scotch and One Beerrdquo of whicha synthesized version was in the works

Initially Beauty and Oro seemed to manifest effects of the longhiatus in the form of low response rates (not enough to earn 50 pel-lets in a session) and some transient difficulties operating the buttonand taking pellets from the nipple However even allowing for somerelearning and the reduced size of the new stimuli the immediacywith which all 3 subjects exhibited highly accurate discriminationsuggests that the original discrimination training had been retained(compare the leftmost sessions in Figure 11 with the rightmost inFigure 9)

Procedure The new stimuli were musically simplif ied MIDIkeyboard renditions of music of the types the f ish had alreadylearned to classify S+ was the familiar blues song described aboveand S was the unfamiliar Fugue 2 from Book I of Bachrsquos Well-Tempered Clavier To minimize the presence of extraneous cues allthe performances were done by the same musician with the sameequipment (a Kurzweil Model k2000vp keyboard Young Chang Re-search and Development Institute Waltham MA) the same se-quencing software (Studio Vision Pro Version 40 Opcode SystemsNashville TN) and the same settings for volume and for timbre(acoustic piano) Because the new stimuli were so short that theywould repeat after only a few trials rote memory could play a rolein their discrimination and thus the operative level of stimulus con-trol was being allowed to potentially regress from categorization todiscrimination

The initial synthetic stimuli turned out to trigger a deteriorationin classification accuracy (Figure 11 Session 13) It seemed possi-ble that this was an artifact of the musical translation process be-cause even humans had some difficulty recognizing the John LeeHooker song in synthetic form It had gone from bluesy to bouncyits original bass inflections were absent and there was no melodicvoice comparable with that of the singer Therefore at Session 24 Iintroduced a second generation of stimuli S+ remained the samepiece but the performance was somewhat more faithful to themodel The old S (the Bach fugue) had been much shorter than S+and thus had been repeating more often so it was replaced by a syn-

thesized rendition of the f irst movement of Vivaldirsquos ConcertoGrosso in A minor Opus 3 No 6 whose duration more closelymatched that of S+ In addition the timbre of the blues was changedfrom acoustic piano to rock piano thus adding timbre as an availablediscriminant However from Session 47 until the end of the experi-ment S+ and S again had timbre in common specifically rockpiano (starting in Session 47) chiffloot (starting in Session 55) andguitar (starting in Session 62)

ResultsWith the first presentations in a synthetic timbre discrim-

ination accuracy deteriorated (Figure 11 Sessions 13ndash23)perhaps because the first synthetic S+ was not a good enoughexemplar of the blues genre Pepi essentially ceased re-sponding during this time and had to be dropped from thestudy Starting at Session 24 with improved stimuli and adifference in timbre between S+ and S the behavior ofboth remaining subjects immediately changed and there-after their discriminative accuracy improved continually

When S+ and S were again made identical in timbre(Session 47) accurate classification persisted despite aperformance decrement probably related to the loss of asalient cue When the same pair of MIDI sequences waspresented in additional timbres generalization of accurateclassification to the new sounds appeared seamless The datafrom Session 47 and onward demonstrate [Sessions 18ts(17) gt 16 ps lt 001] that koi are capable of discriminat-ing polyphonic music on the basis of features other thanthe timbre of individual tone sources

EXPERIMENT 4 Discrimination of Melodies

Without Timbre Cues

After observing that instrumental timbre seemed not tobe a necessary discriminant in polyphonic music I inves-tigated whether timbre was necessary for koi to discrimi-nate single-voice musicmdashthat is melodies

MethodIn order to familiarize the subjects with the S+ melody and also

in hopes of rehabilitating Pepi this experiment began with severalsessions of collective exposure to a sound-versus-silence contin-gency CRF signaled by the music that would later be the S+ in thesound-versus-sound discrimination alternated with extinction sig-naled by silence In this group pretraining Pepi was observed bothpressing the button and taking pellets from the nipple but when sub-sequently isolated for melody discrimination sessions he consis-tently shied away from the nipple and again had to be dropped as asubject

The stimuli for the melody discrimination experiment (Figure 12)were all derived from the theme from Paganinirsquos 24th Caprice forsolo violin which is perhaps best known from Rachmaninoff rsquosldquoRhapsody on a Theme by Paganinirdquo S+ was the original melody asperformed on the MIDI keyboard S was derived from S+ by usingthe transformation described by Poli and Previde (1991) By using acomputer to modify the MIDI score S+rsquos order of pitches was re-versed whereas its original order of note durations was retained Inother words the first note of S got the duration of S+rsquos first notebut the pitch of S+rsquos last note the second note of S got the durationof S+rsquos second note but the pitch of S+rsquos next-to-last note and so onThis procedure can be thought of as retaining the rhythm track while

0

1

2

3S

lop

e (

ch

ang

ese

ssio

n)

1 2 3 4

Reversal Number

OroBeauty

Pepi

Figure 10 Experiment 2 (iterated reversals) improvementtrends For Beauty and Oro the improvement rate (Figure 9 re-gression line slopes percentage of nonresponse S trials per ses-sion) increases with each reversal

MUSIC DISCRIMINATIONS BY CARP 349

reversing the pitch track The result is two stimuli that are ldquoidenticalwith respect to their mean frequency note duration and rhythm butnoticeably different in their melodic patternsrdquo (Poli amp Previde 1991p 12) Such a pitch-track-reversed melody differs from a completelybackwards melody only in rhythm sacrificing the linkage betweeneach pitch and its original duration in order to preserve the originalsequence of durations per se (If the original melodymdashunlike the

Rachmaninoffmdashhas a palindromic rhythm track the pitch-track -reversed melody and the completely backwards melody are identical)The melodies were recorded using the same MIDI apparatus as thatdescribed above To enhance clarity the tempo was somewhat slowerthan that of the usual piano performance

Over the course of 53 sessions the instrumental timbre alternatedsix times between strings and acoustic piano but in any given ses-

0

25

50

75

100

Tri

als

wit

h N

o P

res

s

S+

ITI

S-

Beauty

0

25

50

75

100

Tri

als

wit

h N

o P

ress

S+

ITI

S-

Oro

Same Timbre Different Timbre Same Timbre

S+S-ITI

Pepi ceased responding

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 Session Number

S+

ITI

S-

Pepi

Figure 11 Experiment 3 (transition to MIDI and timbre study) percentages of S+ and S trials dur-ing which the fish did not press the button During the first 12 sessions the stimuli consisted of a singletrack from each of the two commercial recordings the subjects had last heard 10 months earlier at theconclusion of the iterated-reversal experiment the immediate resumption of accurate discrimination sug-gests long-term memory of training The circled data points (Sessions 13 and 24) indicate the introduc-tion of the first- and second-generation synthetic music From Session 47 until the end of the experimentS+ and S had identical timbre each boxed data point pair indicates the first presentation of a new tim-bre Session 47 rock piano Session 55 chiffloot and Session 62 guitar Crosses denote silence

350 CHASE

sion S+ and S always had the same timbre The discrimination pro-tocol was unchanged from the previous experiments except that thesession termination trigger was raised from 50 to 55 pellets As a pre-liminary test for a possible perceptual invariance (Hulse Takeuchi ampBraaten 1992) S+ was transposed down a fifth in Sessions 51ndash52

After 53 sessions it was discovered that the MIDI technology hadintroduced artifactual differences between S+ and S A musicallyattuned visitor to the lab detected minor variations in note durationsbetween the two stimuli which apparently had resulted from incor-rect handling of the attackndashsustainndashdecay envelopes of S+rsquos recordednotes There also turned out to be subtle volume differences whichwere said to have resulted from the combination of the MIDI scoreediting process and the volume compression function in the digitalaudio tape (DAT) recorder used to create stimulus master tapesThese differences were confirmed by careful examination of thewaveforms using a computer oscilloscope Therefore a second gen-eration of S was created by direct numerical substitution of the S+pitches into the MIDI score in reverse order and by recording a newmaster tape with all volume compression disabled The correctionswere verified by waveform analysis

After eight sessions with the second-generat ion S both S+ andS were shortened by the removal of each onersquos distinctive initial noteand seven sessions later they were further shortened by the removal oftheir remaining initial six and final four notes The purpose of thesestimulus contractions was to look for behavioral disruption that might

indicate that the subject had been discriminating the melodies on thebasis of such local features as the absolute pitch of the initial note

Results and DiscussionBeautyrsquos performance inexplicably deteriorated to the

point where he had to be dropped as a subjectFigures 13 and 14 report the performance of Oro the only

fish to complete the melody experiment The data showthat without timbre cues Oro clearly discriminated betweenthe two melodies [in each stimulus condition (ie second-generation S first-note-removed and both-ends-clipped)5 final sessions t(4) gt 10 p lt 001]

Oro responded more to S+ than to S even in the veryfirst session with melodic stimuli Familiarization with theS+ during pretraining could well have contributed to thisresponse bias perhaps partly because music heard in asound-versus-silence context had consistently become theS+ in a subsequent sound-versus-sound discriminationHowever the MIDI artifacts in the first-generation stim-uli might also have played a role

Session 54 in which the corrected S was introducedmarks a significant reduction of the separation between

Figure 12 Experiment 4 (melody discrimination) musical scores of the normal (S+) and pitch-reversed (S )melodies

MUSIC DISCRIMINATIONS BY CARP 351

the S+ and the S nonresponse percentages [two-tailed two-sample t test assuming unequal variances contrasting themean difference between S and S+ nonresponse per-centages before and after the change 8 observations just be-fore the stimulus change vs 8 observations just after t(11) =277 p lt 019] This implies that the rather subtle artifactsin the original S had indeed been exploited as discrimi-nants

One oddity is the fact that although the stimuli changedsignificantly in Sessions 54 (second-generation S ) and62 (removal of the first note of S+ and S ) in each case

a pronounced anomaly in Ororsquos performance occurred inthe following session

Studies of melody discrimination in animals have oftenfound that the behavior was controlled by local featuressuch as timbre pitch register or the absolute pitch of the ini-tial note rather than by the melodic patterning per se(DrsquoAmato amp Salmon 1984 Hulse amp Cynx 1985 Hulseamp Page 1988 Poli amp Previde 1991) (In this paper for theterm local properties I follow the convention of referringnot only to features like distinctive individual notes whichare clearly local in a temporal sense but also to features

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 70

Session Number

S+

S-

= Piano= Down a fifth= wo 1st note= wo 1st 7 amp last 4 notes

S+S-ITI

Figure 13 Experiment 4 (melody discrimination) trials with no responses The MIDI timbre was violin except for 13 sessions ofpiano as marked The corrected S was introduced at Session 54 The first notes of S+ and S were removed at Session 62 The sixinitial and four final notes were removed at Session 69 Crosses denote silence

Figure 14 Experiment 4 (melody discrimination) all responses Sessions terminated with the S+ trial in which the 55th pel-let was dispensed Crosses denote silence

0

20

40

60

All

Pre

sses

0 10 20 30 40 50 60 70

Session Number

S+

S-

Oro

S+S-ITI

352 CHASE

like timbre and pitch register which although recogniz-able in any local segment can be constant over the dura-tion of the stimulus and which therefore might arguablybe called global properties) It should not be surprisingthat with sequential stimuli such as sound animals oftenexploit local features in preference to global pattern fea-tures In the acoustic domain features that are instantly rec-ognizable presumably confer a survival advantage not onlyon listeners but also on creatures in whose interest it is tobe identifiable by sounds they make Oro did not have tim-bre available as a discriminant but there is no conclusiveevidence that he did or did not use other local features andit is not known which if any global features he might haveused

It warrants mention that in this type of discriminationexperiment inaccurate responding need not imply that thesubject is musically insensitive because musical sensitiv-ity can actually confound discriminative accuracy if bothstimuli are musically plausible or stylistically similar In-deed throughout this experiment the stimuli were moni-tored through a speaker in the laboratory office and S+ andS became so familiar and the pitch-track-reversed Ssounded so pleasing that human observers occasionallybecame confused as to which reinforcement contingencywas in force in the tank

The finding that Oro did not need timbre cues to dis-criminate melodies contrasts sharply with the result in ratsreported by Poli and Previde (1991) Using as stimuli for-ward and pitch-track-reversed versions of the melodyldquoFregravere Jacquesrdquo they tested for discrimination on the basisof melodic pattern The rats had neither previous experi-mental experience nor prior familiarity with music In anattempt to preclude the exploitation of local features suchas the absolute pitch of distinctively positioned notes each15-sec stimulus presentation began at a randomly chosenposition within the melody Different groups of subjectswere asked to discriminate two melodic stimuli that dif-fered in melody only in timbre only or in both attributesHowever the stimuli were never heard as unitary melodiesfrom start to finish and were presented in a continuousstream of randomly sequenced exposures with responsesin the presence of S+ being reinforced only on an FR-5schedule This would seem to be such a formidable task asto make it unsurprising that animals failed except when tim-bre a consistent property of every note in each stimuluswas available as a discriminant However Poli and Previdedid suggest that rats might well prove able to discriminatemelodies without timbre cues under other conditions

CONCLUDING REMARKS

The distinction between local features and pattern fea-tures although it arose in connection with melody dis-crimination is equally relevant to the categorization ex-periment To say that in classifying music as blues orclassical the koi might have been responding to deepgeneric attributes is not to say that they were necessarilyusing anything other than local cues because the diag-

nostic property could have been a particular combinationof timbre loudness pitch brief rhythmic or melodic fig-ures and other such local features A human scanning aradio dial requires only a fraction of a second to identifythe genre of a given station hardly enough time for patternfeatures to manifest themselves so a brief sample of musiccould well contain something recognizable to an animalthat had a rote store of auditory feature memories Localfeatures might control classification behavior even whenthere is extensive exposure to a stimulus Conceivably an-imals could acquire a functional understanding of musicentirely on the basis of the distribution and frequency ofvarious combinations of essentially local features with-out regard to the artistic pattern features in terms of whichmusical genres are commonly defined

Prior to this series of experiments the prevailing opinionappeared to be skepticism as to whether koi could dis-criminate one piece of music from another under any cir-cumstances Now it appears that these animals can discrim-inate polyphonic music discriminate melodic patternsand even classify music by artistic genre As far as I knowthese experiments presented the most complex auditorystimuli to which fish have ever been shown capable ofmaking sophisticated discriminative responses Howeverthere remains the task of elucidating the stimulus controlfunctions of the constituents of that complexity such aspattern features local features and simple properties of thestimulus as a whole The present work was intended as ex-ploratory rather than explanatory and the results clearly ex-tend the known envelope of auditory capabilities in fish

REFERENCES

Baron M R (1965) The stimulus stimulus control and generaliza-tion In D I Mostovsky (Ed) Stimulus generalization (pp 62-71)Stanford CA Stanford University Press

Chase A R amp Hill W (1999) Reliable operant apparatus for fishAudio stimulus generator response button and pellet-dispensing nip-ple Behavior Research Methods Instruments amp Computers 31 470-478

Coombs S Jannsen J amp Montgomery J C (1992) Functional andevolutionary implications of peripheral diversity in lateral line sys-tems In D B Webster R R Fay amp A N Popper (Eds) The evolu-tionary biology of hearing (pp 267-294) New York Springer-Verlag

DrsquoAmato M R amp Salmon D P (1982) Tune discrimination in mon-keys (Cebus apella) and rats Animal Learning amp Behavior 10 126-134

DrsquoAmato M R amp Salmon D P (1984) Processing of complex au-ditory stimuli (tunes) by rats and monkeys (Cebus apella) AnimalLearning amp Behavior 12 184-194

Fay R R (1988) Hearing in vertebrates A psychophysics data-bookWinnetka IL Hill-Fay Associates

Fay R R (1992) Analytic listening in goldfish Hearing Research 59101-107

Fay R R (1994) Perception of temporal acoustic patterns by the gold-fish (Carassius auratus) Hearing Research 76 158-172

Fay R R (1995) Perception of spectrally and temporally complexsounds by the goldfish (Carassius auratus) Hearing Research 89146-154

Fay R R (1998) Auditory stream segregation in goldfish (Carassiusauratus) Hearing Research 120 69-76

Fay R R amp Ream T J (1986) Acoustic response and tuning in sac-cular nerve fibers of the goldfish (Carassius auratus) Journal of theAcoustical Society of America 79 1883-1895

Hartman W M (1988) Pitch perception and the segregation and inte-

348 CHASE

work resumed with a reintroduction to the apparatus and protocol asleft off at the end of the fourth and final reversalmdashthat is with S+and S being blues and classical respectively However the fishwere also being prepared to encounter the synthetic stimuli that werebeing created at that time which consisted of a single short piecefrom each genre rather than a collection comparable in duration andvariety with the commercial CDs used previously Therefore in pre-training the stimuli were the same two CDs the subjects had lastheard (see Figure 4 Session 300) but only a single track from eachS was an excerpt from a Bach oboe concerto S+ was the John LeeHooker song ldquoOne Bourbon One Scotch and One Beerrdquo of whicha synthesized version was in the works

Initially Beauty and Oro seemed to manifest effects of the longhiatus in the form of low response rates (not enough to earn 50 pel-lets in a session) and some transient difficulties operating the buttonand taking pellets from the nipple However even allowing for somerelearning and the reduced size of the new stimuli the immediacywith which all 3 subjects exhibited highly accurate discriminationsuggests that the original discrimination training had been retained(compare the leftmost sessions in Figure 11 with the rightmost inFigure 9)

Procedure The new stimuli were musically simplif ied MIDIkeyboard renditions of music of the types the f ish had alreadylearned to classify S+ was the familiar blues song described aboveand S was the unfamiliar Fugue 2 from Book I of Bachrsquos Well-Tempered Clavier To minimize the presence of extraneous cues allthe performances were done by the same musician with the sameequipment (a Kurzweil Model k2000vp keyboard Young Chang Re-search and Development Institute Waltham MA) the same se-quencing software (Studio Vision Pro Version 40 Opcode SystemsNashville TN) and the same settings for volume and for timbre(acoustic piano) Because the new stimuli were so short that theywould repeat after only a few trials rote memory could play a rolein their discrimination and thus the operative level of stimulus con-trol was being allowed to potentially regress from categorization todiscrimination

The initial synthetic stimuli turned out to trigger a deteriorationin classification accuracy (Figure 11 Session 13) It seemed possi-ble that this was an artifact of the musical translation process be-cause even humans had some difficulty recognizing the John LeeHooker song in synthetic form It had gone from bluesy to bouncyits original bass inflections were absent and there was no melodicvoice comparable with that of the singer Therefore at Session 24 Iintroduced a second generation of stimuli S+ remained the samepiece but the performance was somewhat more faithful to themodel The old S (the Bach fugue) had been much shorter than S+and thus had been repeating more often so it was replaced by a syn-

thesized rendition of the f irst movement of Vivaldirsquos ConcertoGrosso in A minor Opus 3 No 6 whose duration more closelymatched that of S+ In addition the timbre of the blues was changedfrom acoustic piano to rock piano thus adding timbre as an availablediscriminant However from Session 47 until the end of the experi-ment S+ and S again had timbre in common specifically rockpiano (starting in Session 47) chiffloot (starting in Session 55) andguitar (starting in Session 62)

ResultsWith the first presentations in a synthetic timbre discrim-

ination accuracy deteriorated (Figure 11 Sessions 13ndash23)perhaps because the first synthetic S+ was not a good enoughexemplar of the blues genre Pepi essentially ceased re-sponding during this time and had to be dropped from thestudy Starting at Session 24 with improved stimuli and adifference in timbre between S+ and S the behavior ofboth remaining subjects immediately changed and there-after their discriminative accuracy improved continually

When S+ and S were again made identical in timbre(Session 47) accurate classification persisted despite aperformance decrement probably related to the loss of asalient cue When the same pair of MIDI sequences waspresented in additional timbres generalization of accurateclassification to the new sounds appeared seamless The datafrom Session 47 and onward demonstrate [Sessions 18ts(17) gt 16 ps lt 001] that koi are capable of discriminat-ing polyphonic music on the basis of features other thanthe timbre of individual tone sources

EXPERIMENT 4 Discrimination of Melodies

Without Timbre Cues

After observing that instrumental timbre seemed not tobe a necessary discriminant in polyphonic music I inves-tigated whether timbre was necessary for koi to discrimi-nate single-voice musicmdashthat is melodies

MethodIn order to familiarize the subjects with the S+ melody and also

in hopes of rehabilitating Pepi this experiment began with severalsessions of collective exposure to a sound-versus-silence contin-gency CRF signaled by the music that would later be the S+ in thesound-versus-sound discrimination alternated with extinction sig-naled by silence In this group pretraining Pepi was observed bothpressing the button and taking pellets from the nipple but when sub-sequently isolated for melody discrimination sessions he consis-tently shied away from the nipple and again had to be dropped as asubject

The stimuli for the melody discrimination experiment (Figure 12)were all derived from the theme from Paganinirsquos 24th Caprice forsolo violin which is perhaps best known from Rachmaninoff rsquosldquoRhapsody on a Theme by Paganinirdquo S+ was the original melody asperformed on the MIDI keyboard S was derived from S+ by usingthe transformation described by Poli and Previde (1991) By using acomputer to modify the MIDI score S+rsquos order of pitches was re-versed whereas its original order of note durations was retained Inother words the first note of S got the duration of S+rsquos first notebut the pitch of S+rsquos last note the second note of S got the durationof S+rsquos second note but the pitch of S+rsquos next-to-last note and so onThis procedure can be thought of as retaining the rhythm track while

0

1

2

3S

lop

e (

ch

ang

ese

ssio

n)

1 2 3 4

Reversal Number

OroBeauty

Pepi

Figure 10 Experiment 2 (iterated reversals) improvementtrends For Beauty and Oro the improvement rate (Figure 9 re-gression line slopes percentage of nonresponse S trials per ses-sion) increases with each reversal

MUSIC DISCRIMINATIONS BY CARP 349

reversing the pitch track The result is two stimuli that are ldquoidenticalwith respect to their mean frequency note duration and rhythm butnoticeably different in their melodic patternsrdquo (Poli amp Previde 1991p 12) Such a pitch-track-reversed melody differs from a completelybackwards melody only in rhythm sacrificing the linkage betweeneach pitch and its original duration in order to preserve the originalsequence of durations per se (If the original melodymdashunlike the

Rachmaninoffmdashhas a palindromic rhythm track the pitch-track -reversed melody and the completely backwards melody are identical)The melodies were recorded using the same MIDI apparatus as thatdescribed above To enhance clarity the tempo was somewhat slowerthan that of the usual piano performance

Over the course of 53 sessions the instrumental timbre alternatedsix times between strings and acoustic piano but in any given ses-

0

25

50

75

100

Tri

als

wit

h N

o P

res

s

S+

ITI

S-

Beauty

0

25

50

75

100

Tri

als

wit

h N

o P

ress

S+

ITI

S-

Oro

Same Timbre Different Timbre Same Timbre

S+S-ITI

Pepi ceased responding

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 Session Number

S+

ITI

S-

Pepi

Figure 11 Experiment 3 (transition to MIDI and timbre study) percentages of S+ and S trials dur-ing which the fish did not press the button During the first 12 sessions the stimuli consisted of a singletrack from each of the two commercial recordings the subjects had last heard 10 months earlier at theconclusion of the iterated-reversal experiment the immediate resumption of accurate discrimination sug-gests long-term memory of training The circled data points (Sessions 13 and 24) indicate the introduc-tion of the first- and second-generation synthetic music From Session 47 until the end of the experimentS+ and S had identical timbre each boxed data point pair indicates the first presentation of a new tim-bre Session 47 rock piano Session 55 chiffloot and Session 62 guitar Crosses denote silence

350 CHASE

sion S+ and S always had the same timbre The discrimination pro-tocol was unchanged from the previous experiments except that thesession termination trigger was raised from 50 to 55 pellets As a pre-liminary test for a possible perceptual invariance (Hulse Takeuchi ampBraaten 1992) S+ was transposed down a fifth in Sessions 51ndash52

After 53 sessions it was discovered that the MIDI technology hadintroduced artifactual differences between S+ and S A musicallyattuned visitor to the lab detected minor variations in note durationsbetween the two stimuli which apparently had resulted from incor-rect handling of the attackndashsustainndashdecay envelopes of S+rsquos recordednotes There also turned out to be subtle volume differences whichwere said to have resulted from the combination of the MIDI scoreediting process and the volume compression function in the digitalaudio tape (DAT) recorder used to create stimulus master tapesThese differences were confirmed by careful examination of thewaveforms using a computer oscilloscope Therefore a second gen-eration of S was created by direct numerical substitution of the S+pitches into the MIDI score in reverse order and by recording a newmaster tape with all volume compression disabled The correctionswere verified by waveform analysis

After eight sessions with the second-generat ion S both S+ andS were shortened by the removal of each onersquos distinctive initial noteand seven sessions later they were further shortened by the removal oftheir remaining initial six and final four notes The purpose of thesestimulus contractions was to look for behavioral disruption that might

indicate that the subject had been discriminating the melodies on thebasis of such local features as the absolute pitch of the initial note

Results and DiscussionBeautyrsquos performance inexplicably deteriorated to the

point where he had to be dropped as a subjectFigures 13 and 14 report the performance of Oro the only

fish to complete the melody experiment The data showthat without timbre cues Oro clearly discriminated betweenthe two melodies [in each stimulus condition (ie second-generation S first-note-removed and both-ends-clipped)5 final sessions t(4) gt 10 p lt 001]

Oro responded more to S+ than to S even in the veryfirst session with melodic stimuli Familiarization with theS+ during pretraining could well have contributed to thisresponse bias perhaps partly because music heard in asound-versus-silence context had consistently become theS+ in a subsequent sound-versus-sound discriminationHowever the MIDI artifacts in the first-generation stim-uli might also have played a role

Session 54 in which the corrected S was introducedmarks a significant reduction of the separation between

Figure 12 Experiment 4 (melody discrimination) musical scores of the normal (S+) and pitch-reversed (S )melodies

MUSIC DISCRIMINATIONS BY CARP 351

the S+ and the S nonresponse percentages [two-tailed two-sample t test assuming unequal variances contrasting themean difference between S and S+ nonresponse per-centages before and after the change 8 observations just be-fore the stimulus change vs 8 observations just after t(11) =277 p lt 019] This implies that the rather subtle artifactsin the original S had indeed been exploited as discrimi-nants

One oddity is the fact that although the stimuli changedsignificantly in Sessions 54 (second-generation S ) and62 (removal of the first note of S+ and S ) in each case

a pronounced anomaly in Ororsquos performance occurred inthe following session

Studies of melody discrimination in animals have oftenfound that the behavior was controlled by local featuressuch as timbre pitch register or the absolute pitch of the ini-tial note rather than by the melodic patterning per se(DrsquoAmato amp Salmon 1984 Hulse amp Cynx 1985 Hulseamp Page 1988 Poli amp Previde 1991) (In this paper for theterm local properties I follow the convention of referringnot only to features like distinctive individual notes whichare clearly local in a temporal sense but also to features

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 70

Session Number

S+

S-

= Piano= Down a fifth= wo 1st note= wo 1st 7 amp last 4 notes

S+S-ITI

Figure 13 Experiment 4 (melody discrimination) trials with no responses The MIDI timbre was violin except for 13 sessions ofpiano as marked The corrected S was introduced at Session 54 The first notes of S+ and S were removed at Session 62 The sixinitial and four final notes were removed at Session 69 Crosses denote silence

Figure 14 Experiment 4 (melody discrimination) all responses Sessions terminated with the S+ trial in which the 55th pel-let was dispensed Crosses denote silence

0

20

40

60

All

Pre

sses

0 10 20 30 40 50 60 70

Session Number

S+

S-

Oro

S+S-ITI

352 CHASE

like timbre and pitch register which although recogniz-able in any local segment can be constant over the dura-tion of the stimulus and which therefore might arguablybe called global properties) It should not be surprisingthat with sequential stimuli such as sound animals oftenexploit local features in preference to global pattern fea-tures In the acoustic domain features that are instantly rec-ognizable presumably confer a survival advantage not onlyon listeners but also on creatures in whose interest it is tobe identifiable by sounds they make Oro did not have tim-bre available as a discriminant but there is no conclusiveevidence that he did or did not use other local features andit is not known which if any global features he might haveused

It warrants mention that in this type of discriminationexperiment inaccurate responding need not imply that thesubject is musically insensitive because musical sensitiv-ity can actually confound discriminative accuracy if bothstimuli are musically plausible or stylistically similar In-deed throughout this experiment the stimuli were moni-tored through a speaker in the laboratory office and S+ andS became so familiar and the pitch-track-reversed Ssounded so pleasing that human observers occasionallybecame confused as to which reinforcement contingencywas in force in the tank

The finding that Oro did not need timbre cues to dis-criminate melodies contrasts sharply with the result in ratsreported by Poli and Previde (1991) Using as stimuli for-ward and pitch-track-reversed versions of the melodyldquoFregravere Jacquesrdquo they tested for discrimination on the basisof melodic pattern The rats had neither previous experi-mental experience nor prior familiarity with music In anattempt to preclude the exploitation of local features suchas the absolute pitch of distinctively positioned notes each15-sec stimulus presentation began at a randomly chosenposition within the melody Different groups of subjectswere asked to discriminate two melodic stimuli that dif-fered in melody only in timbre only or in both attributesHowever the stimuli were never heard as unitary melodiesfrom start to finish and were presented in a continuousstream of randomly sequenced exposures with responsesin the presence of S+ being reinforced only on an FR-5schedule This would seem to be such a formidable task asto make it unsurprising that animals failed except when tim-bre a consistent property of every note in each stimuluswas available as a discriminant However Poli and Previdedid suggest that rats might well prove able to discriminatemelodies without timbre cues under other conditions

CONCLUDING REMARKS

The distinction between local features and pattern fea-tures although it arose in connection with melody dis-crimination is equally relevant to the categorization ex-periment To say that in classifying music as blues orclassical the koi might have been responding to deepgeneric attributes is not to say that they were necessarilyusing anything other than local cues because the diag-

nostic property could have been a particular combinationof timbre loudness pitch brief rhythmic or melodic fig-ures and other such local features A human scanning aradio dial requires only a fraction of a second to identifythe genre of a given station hardly enough time for patternfeatures to manifest themselves so a brief sample of musiccould well contain something recognizable to an animalthat had a rote store of auditory feature memories Localfeatures might control classification behavior even whenthere is extensive exposure to a stimulus Conceivably an-imals could acquire a functional understanding of musicentirely on the basis of the distribution and frequency ofvarious combinations of essentially local features with-out regard to the artistic pattern features in terms of whichmusical genres are commonly defined

Prior to this series of experiments the prevailing opinionappeared to be skepticism as to whether koi could dis-criminate one piece of music from another under any cir-cumstances Now it appears that these animals can discrim-inate polyphonic music discriminate melodic patternsand even classify music by artistic genre As far as I knowthese experiments presented the most complex auditorystimuli to which fish have ever been shown capable ofmaking sophisticated discriminative responses Howeverthere remains the task of elucidating the stimulus controlfunctions of the constituents of that complexity such aspattern features local features and simple properties of thestimulus as a whole The present work was intended as ex-ploratory rather than explanatory and the results clearly ex-tend the known envelope of auditory capabilities in fish

REFERENCES

Baron M R (1965) The stimulus stimulus control and generaliza-tion In D I Mostovsky (Ed) Stimulus generalization (pp 62-71)Stanford CA Stanford University Press

Chase A R amp Hill W (1999) Reliable operant apparatus for fishAudio stimulus generator response button and pellet-dispensing nip-ple Behavior Research Methods Instruments amp Computers 31 470-478

Coombs S Jannsen J amp Montgomery J C (1992) Functional andevolutionary implications of peripheral diversity in lateral line sys-tems In D B Webster R R Fay amp A N Popper (Eds) The evolu-tionary biology of hearing (pp 267-294) New York Springer-Verlag

DrsquoAmato M R amp Salmon D P (1982) Tune discrimination in mon-keys (Cebus apella) and rats Animal Learning amp Behavior 10 126-134

DrsquoAmato M R amp Salmon D P (1984) Processing of complex au-ditory stimuli (tunes) by rats and monkeys (Cebus apella) AnimalLearning amp Behavior 12 184-194

Fay R R (1988) Hearing in vertebrates A psychophysics data-bookWinnetka IL Hill-Fay Associates

Fay R R (1992) Analytic listening in goldfish Hearing Research 59101-107

Fay R R (1994) Perception of temporal acoustic patterns by the gold-fish (Carassius auratus) Hearing Research 76 158-172

Fay R R (1995) Perception of spectrally and temporally complexsounds by the goldfish (Carassius auratus) Hearing Research 89146-154

Fay R R (1998) Auditory stream segregation in goldfish (Carassiusauratus) Hearing Research 120 69-76

Fay R R amp Ream T J (1986) Acoustic response and tuning in sac-cular nerve fibers of the goldfish (Carassius auratus) Journal of theAcoustical Society of America 79 1883-1895

Hartman W M (1988) Pitch perception and the segregation and inte-

MUSIC DISCRIMINATIONS BY CARP 349

reversing the pitch track The result is two stimuli that are ldquoidenticalwith respect to their mean frequency note duration and rhythm butnoticeably different in their melodic patternsrdquo (Poli amp Previde 1991p 12) Such a pitch-track-reversed melody differs from a completelybackwards melody only in rhythm sacrificing the linkage betweeneach pitch and its original duration in order to preserve the originalsequence of durations per se (If the original melodymdashunlike the

Rachmaninoffmdashhas a palindromic rhythm track the pitch-track -reversed melody and the completely backwards melody are identical)The melodies were recorded using the same MIDI apparatus as thatdescribed above To enhance clarity the tempo was somewhat slowerthan that of the usual piano performance

Over the course of 53 sessions the instrumental timbre alternatedsix times between strings and acoustic piano but in any given ses-

0

25

50

75

100

Tri

als

wit

h N

o P

res

s

S+

ITI

S-

Beauty

0

25

50

75

100

Tri

als

wit

h N

o P

ress

S+

ITI

S-

Oro

Same Timbre Different Timbre Same Timbre

S+S-ITI

Pepi ceased responding

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 Session Number

S+

ITI

S-

Pepi

Figure 11 Experiment 3 (transition to MIDI and timbre study) percentages of S+ and S trials dur-ing which the fish did not press the button During the first 12 sessions the stimuli consisted of a singletrack from each of the two commercial recordings the subjects had last heard 10 months earlier at theconclusion of the iterated-reversal experiment the immediate resumption of accurate discrimination sug-gests long-term memory of training The circled data points (Sessions 13 and 24) indicate the introduc-tion of the first- and second-generation synthetic music From Session 47 until the end of the experimentS+ and S had identical timbre each boxed data point pair indicates the first presentation of a new tim-bre Session 47 rock piano Session 55 chiffloot and Session 62 guitar Crosses denote silence

350 CHASE

sion S+ and S always had the same timbre The discrimination pro-tocol was unchanged from the previous experiments except that thesession termination trigger was raised from 50 to 55 pellets As a pre-liminary test for a possible perceptual invariance (Hulse Takeuchi ampBraaten 1992) S+ was transposed down a fifth in Sessions 51ndash52

After 53 sessions it was discovered that the MIDI technology hadintroduced artifactual differences between S+ and S A musicallyattuned visitor to the lab detected minor variations in note durationsbetween the two stimuli which apparently had resulted from incor-rect handling of the attackndashsustainndashdecay envelopes of S+rsquos recordednotes There also turned out to be subtle volume differences whichwere said to have resulted from the combination of the MIDI scoreediting process and the volume compression function in the digitalaudio tape (DAT) recorder used to create stimulus master tapesThese differences were confirmed by careful examination of thewaveforms using a computer oscilloscope Therefore a second gen-eration of S was created by direct numerical substitution of the S+pitches into the MIDI score in reverse order and by recording a newmaster tape with all volume compression disabled The correctionswere verified by waveform analysis

After eight sessions with the second-generat ion S both S+ andS were shortened by the removal of each onersquos distinctive initial noteand seven sessions later they were further shortened by the removal oftheir remaining initial six and final four notes The purpose of thesestimulus contractions was to look for behavioral disruption that might

indicate that the subject had been discriminating the melodies on thebasis of such local features as the absolute pitch of the initial note

Results and DiscussionBeautyrsquos performance inexplicably deteriorated to the

point where he had to be dropped as a subjectFigures 13 and 14 report the performance of Oro the only

fish to complete the melody experiment The data showthat without timbre cues Oro clearly discriminated betweenthe two melodies [in each stimulus condition (ie second-generation S first-note-removed and both-ends-clipped)5 final sessions t(4) gt 10 p lt 001]

Oro responded more to S+ than to S even in the veryfirst session with melodic stimuli Familiarization with theS+ during pretraining could well have contributed to thisresponse bias perhaps partly because music heard in asound-versus-silence context had consistently become theS+ in a subsequent sound-versus-sound discriminationHowever the MIDI artifacts in the first-generation stim-uli might also have played a role

Session 54 in which the corrected S was introducedmarks a significant reduction of the separation between

Figure 12 Experiment 4 (melody discrimination) musical scores of the normal (S+) and pitch-reversed (S )melodies

MUSIC DISCRIMINATIONS BY CARP 351

the S+ and the S nonresponse percentages [two-tailed two-sample t test assuming unequal variances contrasting themean difference between S and S+ nonresponse per-centages before and after the change 8 observations just be-fore the stimulus change vs 8 observations just after t(11) =277 p lt 019] This implies that the rather subtle artifactsin the original S had indeed been exploited as discrimi-nants

One oddity is the fact that although the stimuli changedsignificantly in Sessions 54 (second-generation S ) and62 (removal of the first note of S+ and S ) in each case

a pronounced anomaly in Ororsquos performance occurred inthe following session

Studies of melody discrimination in animals have oftenfound that the behavior was controlled by local featuressuch as timbre pitch register or the absolute pitch of the ini-tial note rather than by the melodic patterning per se(DrsquoAmato amp Salmon 1984 Hulse amp Cynx 1985 Hulseamp Page 1988 Poli amp Previde 1991) (In this paper for theterm local properties I follow the convention of referringnot only to features like distinctive individual notes whichare clearly local in a temporal sense but also to features

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 70

Session Number

S+

S-

= Piano= Down a fifth= wo 1st note= wo 1st 7 amp last 4 notes

S+S-ITI

Figure 13 Experiment 4 (melody discrimination) trials with no responses The MIDI timbre was violin except for 13 sessions ofpiano as marked The corrected S was introduced at Session 54 The first notes of S+ and S were removed at Session 62 The sixinitial and four final notes were removed at Session 69 Crosses denote silence

Figure 14 Experiment 4 (melody discrimination) all responses Sessions terminated with the S+ trial in which the 55th pel-let was dispensed Crosses denote silence

0

20

40

60

All

Pre

sses

0 10 20 30 40 50 60 70

Session Number

S+

S-

Oro

S+S-ITI

352 CHASE

like timbre and pitch register which although recogniz-able in any local segment can be constant over the dura-tion of the stimulus and which therefore might arguablybe called global properties) It should not be surprisingthat with sequential stimuli such as sound animals oftenexploit local features in preference to global pattern fea-tures In the acoustic domain features that are instantly rec-ognizable presumably confer a survival advantage not onlyon listeners but also on creatures in whose interest it is tobe identifiable by sounds they make Oro did not have tim-bre available as a discriminant but there is no conclusiveevidence that he did or did not use other local features andit is not known which if any global features he might haveused

It warrants mention that in this type of discriminationexperiment inaccurate responding need not imply that thesubject is musically insensitive because musical sensitiv-ity can actually confound discriminative accuracy if bothstimuli are musically plausible or stylistically similar In-deed throughout this experiment the stimuli were moni-tored through a speaker in the laboratory office and S+ andS became so familiar and the pitch-track-reversed Ssounded so pleasing that human observers occasionallybecame confused as to which reinforcement contingencywas in force in the tank

The finding that Oro did not need timbre cues to dis-criminate melodies contrasts sharply with the result in ratsreported by Poli and Previde (1991) Using as stimuli for-ward and pitch-track-reversed versions of the melodyldquoFregravere Jacquesrdquo they tested for discrimination on the basisof melodic pattern The rats had neither previous experi-mental experience nor prior familiarity with music In anattempt to preclude the exploitation of local features suchas the absolute pitch of distinctively positioned notes each15-sec stimulus presentation began at a randomly chosenposition within the melody Different groups of subjectswere asked to discriminate two melodic stimuli that dif-fered in melody only in timbre only or in both attributesHowever the stimuli were never heard as unitary melodiesfrom start to finish and were presented in a continuousstream of randomly sequenced exposures with responsesin the presence of S+ being reinforced only on an FR-5schedule This would seem to be such a formidable task asto make it unsurprising that animals failed except when tim-bre a consistent property of every note in each stimuluswas available as a discriminant However Poli and Previdedid suggest that rats might well prove able to discriminatemelodies without timbre cues under other conditions

CONCLUDING REMARKS

The distinction between local features and pattern fea-tures although it arose in connection with melody dis-crimination is equally relevant to the categorization ex-periment To say that in classifying music as blues orclassical the koi might have been responding to deepgeneric attributes is not to say that they were necessarilyusing anything other than local cues because the diag-

nostic property could have been a particular combinationof timbre loudness pitch brief rhythmic or melodic fig-ures and other such local features A human scanning aradio dial requires only a fraction of a second to identifythe genre of a given station hardly enough time for patternfeatures to manifest themselves so a brief sample of musiccould well contain something recognizable to an animalthat had a rote store of auditory feature memories Localfeatures might control classification behavior even whenthere is extensive exposure to a stimulus Conceivably an-imals could acquire a functional understanding of musicentirely on the basis of the distribution and frequency ofvarious combinations of essentially local features with-out regard to the artistic pattern features in terms of whichmusical genres are commonly defined

Prior to this series of experiments the prevailing opinionappeared to be skepticism as to whether koi could dis-criminate one piece of music from another under any cir-cumstances Now it appears that these animals can discrim-inate polyphonic music discriminate melodic patternsand even classify music by artistic genre As far as I knowthese experiments presented the most complex auditorystimuli to which fish have ever been shown capable ofmaking sophisticated discriminative responses Howeverthere remains the task of elucidating the stimulus controlfunctions of the constituents of that complexity such aspattern features local features and simple properties of thestimulus as a whole The present work was intended as ex-ploratory rather than explanatory and the results clearly ex-tend the known envelope of auditory capabilities in fish

REFERENCES

Baron M R (1965) The stimulus stimulus control and generaliza-tion In D I Mostovsky (Ed) Stimulus generalization (pp 62-71)Stanford CA Stanford University Press

Chase A R amp Hill W (1999) Reliable operant apparatus for fishAudio stimulus generator response button and pellet-dispensing nip-ple Behavior Research Methods Instruments amp Computers 31 470-478

Coombs S Jannsen J amp Montgomery J C (1992) Functional andevolutionary implications of peripheral diversity in lateral line sys-tems In D B Webster R R Fay amp A N Popper (Eds) The evolu-tionary biology of hearing (pp 267-294) New York Springer-Verlag

DrsquoAmato M R amp Salmon D P (1982) Tune discrimination in mon-keys (Cebus apella) and rats Animal Learning amp Behavior 10 126-134

DrsquoAmato M R amp Salmon D P (1984) Processing of complex au-ditory stimuli (tunes) by rats and monkeys (Cebus apella) AnimalLearning amp Behavior 12 184-194

Fay R R (1988) Hearing in vertebrates A psychophysics data-bookWinnetka IL Hill-Fay Associates

Fay R R (1992) Analytic listening in goldfish Hearing Research 59101-107

Fay R R (1994) Perception of temporal acoustic patterns by the gold-fish (Carassius auratus) Hearing Research 76 158-172

Fay R R (1995) Perception of spectrally and temporally complexsounds by the goldfish (Carassius auratus) Hearing Research 89146-154

Fay R R (1998) Auditory stream segregation in goldfish (Carassiusauratus) Hearing Research 120 69-76

Fay R R amp Ream T J (1986) Acoustic response and tuning in sac-cular nerve fibers of the goldfish (Carassius auratus) Journal of theAcoustical Society of America 79 1883-1895

Hartman W M (1988) Pitch perception and the segregation and inte-

350 CHASE

sion S+ and S always had the same timbre The discrimination pro-tocol was unchanged from the previous experiments except that thesession termination trigger was raised from 50 to 55 pellets As a pre-liminary test for a possible perceptual invariance (Hulse Takeuchi ampBraaten 1992) S+ was transposed down a fifth in Sessions 51ndash52

After 53 sessions it was discovered that the MIDI technology hadintroduced artifactual differences between S+ and S A musicallyattuned visitor to the lab detected minor variations in note durationsbetween the two stimuli which apparently had resulted from incor-rect handling of the attackndashsustainndashdecay envelopes of S+rsquos recordednotes There also turned out to be subtle volume differences whichwere said to have resulted from the combination of the MIDI scoreediting process and the volume compression function in the digitalaudio tape (DAT) recorder used to create stimulus master tapesThese differences were confirmed by careful examination of thewaveforms using a computer oscilloscope Therefore a second gen-eration of S was created by direct numerical substitution of the S+pitches into the MIDI score in reverse order and by recording a newmaster tape with all volume compression disabled The correctionswere verified by waveform analysis

After eight sessions with the second-generat ion S both S+ andS were shortened by the removal of each onersquos distinctive initial noteand seven sessions later they were further shortened by the removal oftheir remaining initial six and final four notes The purpose of thesestimulus contractions was to look for behavioral disruption that might

indicate that the subject had been discriminating the melodies on thebasis of such local features as the absolute pitch of the initial note

Results and DiscussionBeautyrsquos performance inexplicably deteriorated to the

point where he had to be dropped as a subjectFigures 13 and 14 report the performance of Oro the only

fish to complete the melody experiment The data showthat without timbre cues Oro clearly discriminated betweenthe two melodies [in each stimulus condition (ie second-generation S first-note-removed and both-ends-clipped)5 final sessions t(4) gt 10 p lt 001]

Oro responded more to S+ than to S even in the veryfirst session with melodic stimuli Familiarization with theS+ during pretraining could well have contributed to thisresponse bias perhaps partly because music heard in asound-versus-silence context had consistently become theS+ in a subsequent sound-versus-sound discriminationHowever the MIDI artifacts in the first-generation stim-uli might also have played a role

Session 54 in which the corrected S was introducedmarks a significant reduction of the separation between

Figure 12 Experiment 4 (melody discrimination) musical scores of the normal (S+) and pitch-reversed (S )melodies

MUSIC DISCRIMINATIONS BY CARP 351

the S+ and the S nonresponse percentages [two-tailed two-sample t test assuming unequal variances contrasting themean difference between S and S+ nonresponse per-centages before and after the change 8 observations just be-fore the stimulus change vs 8 observations just after t(11) =277 p lt 019] This implies that the rather subtle artifactsin the original S had indeed been exploited as discrimi-nants

One oddity is the fact that although the stimuli changedsignificantly in Sessions 54 (second-generation S ) and62 (removal of the first note of S+ and S ) in each case

a pronounced anomaly in Ororsquos performance occurred inthe following session

Studies of melody discrimination in animals have oftenfound that the behavior was controlled by local featuressuch as timbre pitch register or the absolute pitch of the ini-tial note rather than by the melodic patterning per se(DrsquoAmato amp Salmon 1984 Hulse amp Cynx 1985 Hulseamp Page 1988 Poli amp Previde 1991) (In this paper for theterm local properties I follow the convention of referringnot only to features like distinctive individual notes whichare clearly local in a temporal sense but also to features

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 70

Session Number

S+

S-

= Piano= Down a fifth= wo 1st note= wo 1st 7 amp last 4 notes

S+S-ITI

Figure 13 Experiment 4 (melody discrimination) trials with no responses The MIDI timbre was violin except for 13 sessions ofpiano as marked The corrected S was introduced at Session 54 The first notes of S+ and S were removed at Session 62 The sixinitial and four final notes were removed at Session 69 Crosses denote silence

Figure 14 Experiment 4 (melody discrimination) all responses Sessions terminated with the S+ trial in which the 55th pel-let was dispensed Crosses denote silence

0

20

40

60

All

Pre

sses

0 10 20 30 40 50 60 70

Session Number

S+

S-

Oro

S+S-ITI

352 CHASE

like timbre and pitch register which although recogniz-able in any local segment can be constant over the dura-tion of the stimulus and which therefore might arguablybe called global properties) It should not be surprisingthat with sequential stimuli such as sound animals oftenexploit local features in preference to global pattern fea-tures In the acoustic domain features that are instantly rec-ognizable presumably confer a survival advantage not onlyon listeners but also on creatures in whose interest it is tobe identifiable by sounds they make Oro did not have tim-bre available as a discriminant but there is no conclusiveevidence that he did or did not use other local features andit is not known which if any global features he might haveused

It warrants mention that in this type of discriminationexperiment inaccurate responding need not imply that thesubject is musically insensitive because musical sensitiv-ity can actually confound discriminative accuracy if bothstimuli are musically plausible or stylistically similar In-deed throughout this experiment the stimuli were moni-tored through a speaker in the laboratory office and S+ andS became so familiar and the pitch-track-reversed Ssounded so pleasing that human observers occasionallybecame confused as to which reinforcement contingencywas in force in the tank

The finding that Oro did not need timbre cues to dis-criminate melodies contrasts sharply with the result in ratsreported by Poli and Previde (1991) Using as stimuli for-ward and pitch-track-reversed versions of the melodyldquoFregravere Jacquesrdquo they tested for discrimination on the basisof melodic pattern The rats had neither previous experi-mental experience nor prior familiarity with music In anattempt to preclude the exploitation of local features suchas the absolute pitch of distinctively positioned notes each15-sec stimulus presentation began at a randomly chosenposition within the melody Different groups of subjectswere asked to discriminate two melodic stimuli that dif-fered in melody only in timbre only or in both attributesHowever the stimuli were never heard as unitary melodiesfrom start to finish and were presented in a continuousstream of randomly sequenced exposures with responsesin the presence of S+ being reinforced only on an FR-5schedule This would seem to be such a formidable task asto make it unsurprising that animals failed except when tim-bre a consistent property of every note in each stimuluswas available as a discriminant However Poli and Previdedid suggest that rats might well prove able to discriminatemelodies without timbre cues under other conditions

CONCLUDING REMARKS

The distinction between local features and pattern fea-tures although it arose in connection with melody dis-crimination is equally relevant to the categorization ex-periment To say that in classifying music as blues orclassical the koi might have been responding to deepgeneric attributes is not to say that they were necessarilyusing anything other than local cues because the diag-

nostic property could have been a particular combinationof timbre loudness pitch brief rhythmic or melodic fig-ures and other such local features A human scanning aradio dial requires only a fraction of a second to identifythe genre of a given station hardly enough time for patternfeatures to manifest themselves so a brief sample of musiccould well contain something recognizable to an animalthat had a rote store of auditory feature memories Localfeatures might control classification behavior even whenthere is extensive exposure to a stimulus Conceivably an-imals could acquire a functional understanding of musicentirely on the basis of the distribution and frequency ofvarious combinations of essentially local features with-out regard to the artistic pattern features in terms of whichmusical genres are commonly defined

Prior to this series of experiments the prevailing opinionappeared to be skepticism as to whether koi could dis-criminate one piece of music from another under any cir-cumstances Now it appears that these animals can discrim-inate polyphonic music discriminate melodic patternsand even classify music by artistic genre As far as I knowthese experiments presented the most complex auditorystimuli to which fish have ever been shown capable ofmaking sophisticated discriminative responses Howeverthere remains the task of elucidating the stimulus controlfunctions of the constituents of that complexity such aspattern features local features and simple properties of thestimulus as a whole The present work was intended as ex-ploratory rather than explanatory and the results clearly ex-tend the known envelope of auditory capabilities in fish

REFERENCES

Baron M R (1965) The stimulus stimulus control and generaliza-tion In D I Mostovsky (Ed) Stimulus generalization (pp 62-71)Stanford CA Stanford University Press

Chase A R amp Hill W (1999) Reliable operant apparatus for fishAudio stimulus generator response button and pellet-dispensing nip-ple Behavior Research Methods Instruments amp Computers 31 470-478

Coombs S Jannsen J amp Montgomery J C (1992) Functional andevolutionary implications of peripheral diversity in lateral line sys-tems In D B Webster R R Fay amp A N Popper (Eds) The evolu-tionary biology of hearing (pp 267-294) New York Springer-Verlag

DrsquoAmato M R amp Salmon D P (1982) Tune discrimination in mon-keys (Cebus apella) and rats Animal Learning amp Behavior 10 126-134

DrsquoAmato M R amp Salmon D P (1984) Processing of complex au-ditory stimuli (tunes) by rats and monkeys (Cebus apella) AnimalLearning amp Behavior 12 184-194

Fay R R (1988) Hearing in vertebrates A psychophysics data-bookWinnetka IL Hill-Fay Associates

Fay R R (1992) Analytic listening in goldfish Hearing Research 59101-107

Fay R R (1994) Perception of temporal acoustic patterns by the gold-fish (Carassius auratus) Hearing Research 76 158-172

Fay R R (1995) Perception of spectrally and temporally complexsounds by the goldfish (Carassius auratus) Hearing Research 89146-154

Fay R R (1998) Auditory stream segregation in goldfish (Carassiusauratus) Hearing Research 120 69-76

Fay R R amp Ream T J (1986) Acoustic response and tuning in sac-cular nerve fibers of the goldfish (Carassius auratus) Journal of theAcoustical Society of America 79 1883-1895

Hartman W M (1988) Pitch perception and the segregation and inte-

MUSIC DISCRIMINATIONS BY CARP 351

the S+ and the S nonresponse percentages [two-tailed two-sample t test assuming unequal variances contrasting themean difference between S and S+ nonresponse per-centages before and after the change 8 observations just be-fore the stimulus change vs 8 observations just after t(11) =277 p lt 019] This implies that the rather subtle artifactsin the original S had indeed been exploited as discrimi-nants

One oddity is the fact that although the stimuli changedsignificantly in Sessions 54 (second-generation S ) and62 (removal of the first note of S+ and S ) in each case

a pronounced anomaly in Ororsquos performance occurred inthe following session

Studies of melody discrimination in animals have oftenfound that the behavior was controlled by local featuressuch as timbre pitch register or the absolute pitch of the ini-tial note rather than by the melodic patterning per se(DrsquoAmato amp Salmon 1984 Hulse amp Cynx 1985 Hulseamp Page 1988 Poli amp Previde 1991) (In this paper for theterm local properties I follow the convention of referringnot only to features like distinctive individual notes whichare clearly local in a temporal sense but also to features

0

25

50

75

100

Tri

als

wit

h N

o P

ress

0 10 20 30 40 50 60 70

Session Number

S+

S-

= Piano= Down a fifth= wo 1st note= wo 1st 7 amp last 4 notes

S+S-ITI

Figure 13 Experiment 4 (melody discrimination) trials with no responses The MIDI timbre was violin except for 13 sessions ofpiano as marked The corrected S was introduced at Session 54 The first notes of S+ and S were removed at Session 62 The sixinitial and four final notes were removed at Session 69 Crosses denote silence

Figure 14 Experiment 4 (melody discrimination) all responses Sessions terminated with the S+ trial in which the 55th pel-let was dispensed Crosses denote silence

0

20

40

60

All

Pre

sses

0 10 20 30 40 50 60 70

Session Number

S+

S-

Oro

S+S-ITI

352 CHASE

like timbre and pitch register which although recogniz-able in any local segment can be constant over the dura-tion of the stimulus and which therefore might arguablybe called global properties) It should not be surprisingthat with sequential stimuli such as sound animals oftenexploit local features in preference to global pattern fea-tures In the acoustic domain features that are instantly rec-ognizable presumably confer a survival advantage not onlyon listeners but also on creatures in whose interest it is tobe identifiable by sounds they make Oro did not have tim-bre available as a discriminant but there is no conclusiveevidence that he did or did not use other local features andit is not known which if any global features he might haveused

It warrants mention that in this type of discriminationexperiment inaccurate responding need not imply that thesubject is musically insensitive because musical sensitiv-ity can actually confound discriminative accuracy if bothstimuli are musically plausible or stylistically similar In-deed throughout this experiment the stimuli were moni-tored through a speaker in the laboratory office and S+ andS became so familiar and the pitch-track-reversed Ssounded so pleasing that human observers occasionallybecame confused as to which reinforcement contingencywas in force in the tank

The finding that Oro did not need timbre cues to dis-criminate melodies contrasts sharply with the result in ratsreported by Poli and Previde (1991) Using as stimuli for-ward and pitch-track-reversed versions of the melodyldquoFregravere Jacquesrdquo they tested for discrimination on the basisof melodic pattern The rats had neither previous experi-mental experience nor prior familiarity with music In anattempt to preclude the exploitation of local features suchas the absolute pitch of distinctively positioned notes each15-sec stimulus presentation began at a randomly chosenposition within the melody Different groups of subjectswere asked to discriminate two melodic stimuli that dif-fered in melody only in timbre only or in both attributesHowever the stimuli were never heard as unitary melodiesfrom start to finish and were presented in a continuousstream of randomly sequenced exposures with responsesin the presence of S+ being reinforced only on an FR-5schedule This would seem to be such a formidable task asto make it unsurprising that animals failed except when tim-bre a consistent property of every note in each stimuluswas available as a discriminant However Poli and Previdedid suggest that rats might well prove able to discriminatemelodies without timbre cues under other conditions

CONCLUDING REMARKS

The distinction between local features and pattern fea-tures although it arose in connection with melody dis-crimination is equally relevant to the categorization ex-periment To say that in classifying music as blues orclassical the koi might have been responding to deepgeneric attributes is not to say that they were necessarilyusing anything other than local cues because the diag-

nostic property could have been a particular combinationof timbre loudness pitch brief rhythmic or melodic fig-ures and other such local features A human scanning aradio dial requires only a fraction of a second to identifythe genre of a given station hardly enough time for patternfeatures to manifest themselves so a brief sample of musiccould well contain something recognizable to an animalthat had a rote store of auditory feature memories Localfeatures might control classification behavior even whenthere is extensive exposure to a stimulus Conceivably an-imals could acquire a functional understanding of musicentirely on the basis of the distribution and frequency ofvarious combinations of essentially local features with-out regard to the artistic pattern features in terms of whichmusical genres are commonly defined

Prior to this series of experiments the prevailing opinionappeared to be skepticism as to whether koi could dis-criminate one piece of music from another under any cir-cumstances Now it appears that these animals can discrim-inate polyphonic music discriminate melodic patternsand even classify music by artistic genre As far as I knowthese experiments presented the most complex auditorystimuli to which fish have ever been shown capable ofmaking sophisticated discriminative responses Howeverthere remains the task of elucidating the stimulus controlfunctions of the constituents of that complexity such aspattern features local features and simple properties of thestimulus as a whole The present work was intended as ex-ploratory rather than explanatory and the results clearly ex-tend the known envelope of auditory capabilities in fish

REFERENCES

Baron M R (1965) The stimulus stimulus control and generaliza-tion In D I Mostovsky (Ed) Stimulus generalization (pp 62-71)Stanford CA Stanford University Press

Chase A R amp Hill W (1999) Reliable operant apparatus for fishAudio stimulus generator response button and pellet-dispensing nip-ple Behavior Research Methods Instruments amp Computers 31 470-478

Coombs S Jannsen J amp Montgomery J C (1992) Functional andevolutionary implications of peripheral diversity in lateral line sys-tems In D B Webster R R Fay amp A N Popper (Eds) The evolu-tionary biology of hearing (pp 267-294) New York Springer-Verlag

DrsquoAmato M R amp Salmon D P (1982) Tune discrimination in mon-keys (Cebus apella) and rats Animal Learning amp Behavior 10 126-134

DrsquoAmato M R amp Salmon D P (1984) Processing of complex au-ditory stimuli (tunes) by rats and monkeys (Cebus apella) AnimalLearning amp Behavior 12 184-194

Fay R R (1988) Hearing in vertebrates A psychophysics data-bookWinnetka IL Hill-Fay Associates

Fay R R (1992) Analytic listening in goldfish Hearing Research 59101-107

Fay R R (1994) Perception of temporal acoustic patterns by the gold-fish (Carassius auratus) Hearing Research 76 158-172

Fay R R (1995) Perception of spectrally and temporally complexsounds by the goldfish (Carassius auratus) Hearing Research 89146-154

Fay R R (1998) Auditory stream segregation in goldfish (Carassiusauratus) Hearing Research 120 69-76

Fay R R amp Ream T J (1986) Acoustic response and tuning in sac-cular nerve fibers of the goldfish (Carassius auratus) Journal of theAcoustical Society of America 79 1883-1895

Hartman W M (1988) Pitch perception and the segregation and inte-

352 CHASE

like timbre and pitch register which although recogniz-able in any local segment can be constant over the dura-tion of the stimulus and which therefore might arguablybe called global properties) It should not be surprisingthat with sequential stimuli such as sound animals oftenexploit local features in preference to global pattern fea-tures In the acoustic domain features that are instantly rec-ognizable presumably confer a survival advantage not onlyon listeners but also on creatures in whose interest it is tobe identifiable by sounds they make Oro did not have tim-bre available as a discriminant but there is no conclusiveevidence that he did or did not use other local features andit is not known which if any global features he might haveused

It warrants mention that in this type of discriminationexperiment inaccurate responding need not imply that thesubject is musically insensitive because musical sensitiv-ity can actually confound discriminative accuracy if bothstimuli are musically plausible or stylistically similar In-deed throughout this experiment the stimuli were moni-tored through a speaker in the laboratory office and S+ andS became so familiar and the pitch-track-reversed Ssounded so pleasing that human observers occasionallybecame confused as to which reinforcement contingencywas in force in the tank

The finding that Oro did not need timbre cues to dis-criminate melodies contrasts sharply with the result in ratsreported by Poli and Previde (1991) Using as stimuli for-ward and pitch-track-reversed versions of the melodyldquoFregravere Jacquesrdquo they tested for discrimination on the basisof melodic pattern The rats had neither previous experi-mental experience nor prior familiarity with music In anattempt to preclude the exploitation of local features suchas the absolute pitch of distinctively positioned notes each15-sec stimulus presentation began at a randomly chosenposition within the melody Different groups of subjectswere asked to discriminate two melodic stimuli that dif-fered in melody only in timbre only or in both attributesHowever the stimuli were never heard as unitary melodiesfrom start to finish and were presented in a continuousstream of randomly sequenced exposures with responsesin the presence of S+ being reinforced only on an FR-5schedule This would seem to be such a formidable task asto make it unsurprising that animals failed except when tim-bre a consistent property of every note in each stimuluswas available as a discriminant However Poli and Previdedid suggest that rats might well prove able to discriminatemelodies without timbre cues under other conditions

CONCLUDING REMARKS

The distinction between local features and pattern fea-tures although it arose in connection with melody dis-crimination is equally relevant to the categorization ex-periment To say that in classifying music as blues orclassical the koi might have been responding to deepgeneric attributes is not to say that they were necessarilyusing anything other than local cues because the diag-

nostic property could have been a particular combinationof timbre loudness pitch brief rhythmic or melodic fig-ures and other such local features A human scanning aradio dial requires only a fraction of a second to identifythe genre of a given station hardly enough time for patternfeatures to manifest themselves so a brief sample of musiccould well contain something recognizable to an animalthat had a rote store of auditory feature memories Localfeatures might control classification behavior even whenthere is extensive exposure to a stimulus Conceivably an-imals could acquire a functional understanding of musicentirely on the basis of the distribution and frequency ofvarious combinations of essentially local features with-out regard to the artistic pattern features in terms of whichmusical genres are commonly defined

Prior to this series of experiments the prevailing opinionappeared to be skepticism as to whether koi could dis-criminate one piece of music from another under any cir-cumstances Now it appears that these animals can discrim-inate polyphonic music discriminate melodic patternsand even classify music by artistic genre As far as I knowthese experiments presented the most complex auditorystimuli to which fish have ever been shown capable ofmaking sophisticated discriminative responses Howeverthere remains the task of elucidating the stimulus controlfunctions of the constituents of that complexity such aspattern features local features and simple properties of thestimulus as a whole The present work was intended as ex-ploratory rather than explanatory and the results clearly ex-tend the known envelope of auditory capabilities in fish

REFERENCES

Baron M R (1965) The stimulus stimulus control and generaliza-tion In D I Mostovsky (Ed) Stimulus generalization (pp 62-71)Stanford CA Stanford University Press

Chase A R amp Hill W (1999) Reliable operant apparatus for fishAudio stimulus generator response button and pellet-dispensing nip-ple Behavior Research Methods Instruments amp Computers 31 470-478

Coombs S Jannsen J amp Montgomery J C (1992) Functional andevolutionary implications of peripheral diversity in lateral line sys-tems In D B Webster R R Fay amp A N Popper (Eds) The evolu-tionary biology of hearing (pp 267-294) New York Springer-Verlag

DrsquoAmato M R amp Salmon D P (1982) Tune discrimination in mon-keys (Cebus apella) and rats Animal Learning amp Behavior 10 126-134

DrsquoAmato M R amp Salmon D P (1984) Processing of complex au-ditory stimuli (tunes) by rats and monkeys (Cebus apella) AnimalLearning amp Behavior 12 184-194

Fay R R (1988) Hearing in vertebrates A psychophysics data-bookWinnetka IL Hill-Fay Associates

Fay R R (1992) Analytic listening in goldfish Hearing Research 59101-107

Fay R R (1994) Perception of temporal acoustic patterns by the gold-fish (Carassius auratus) Hearing Research 76 158-172

Fay R R (1995) Perception of spectrally and temporally complexsounds by the goldfish (Carassius auratus) Hearing Research 89146-154

Fay R R (1998) Auditory stream segregation in goldfish (Carassiusauratus) Hearing Research 120 69-76

Fay R R amp Ream T J (1986) Acoustic response and tuning in sac-cular nerve fibers of the goldfish (Carassius auratus) Journal of theAcoustical Society of America 79 1883-1895

Hartman W M (1988) Pitch perception and the segregation and inte-

MUSIC DISCRIMINATIONS BY CARP 353

gration of auditory entities In G M Edelman W E Gall amp W MCowan (Eds) Auditory function Neurological basis of hearing (pp 623-645) New York Wiley

Herrnstein R J (1992) Levels of stimulus control A functional ap-proach In C R Gallistel (Ed) Animal cognition (pp 133-166) Cam-bridge MA MIT Press

Herrnstein R J (1994) Animals as classifiers Lecture given at theRowland Institute for Science Cambridge MA 20 April 1994

Hulse S H amp Cynx J (1985) Relative pitch perception is con-strained by absolute pitch in songbirds (Mimus Molothrus Sturnus)Journal of Comparative Psychology 99 176-196

Hulse S H amp Page S C (1988) Toward a comparative psychologyof music perception Music Perception 5 427-445

Hulse S H Takeuchi A H amp Braaten R F (1992) Perceptual in-variances in the comparative psychology of music Music Perception10 151-184

Jacobs D W amp Tavolga W N (1968) Acoustic frequency discrim-ination in the goldfish Animal Behavior 16 67-71

Malott R W amp Siddall W (1972) Acquisition of the people con-cept in pigeons Psychological Reports 31 3-13

Nelson J S (1984) Fishes of the world (2nd ed) New York WileyPoli M amp Previde E P (1991) Discrimination of musical stimuli by

rats (Rattus norvegicus) International Journal of Comparative Psychol-ogy 5 7-18

Popper A N amp Fay R R (1993) Sound detection and processing byfish Critical review and major research questions Brain Behavior ampEvolution 41 14-38

Popper A N Platt C amp Saidel W (1982) Acoustic functions inthe fish ear Trends in Neurosciences 5 276-280

Porter D amp Neuringer A (1984) Music discriminations by pi-geons Journal of Experimental Psychology Animal Behavior Processes10 138-148

Segal M amp Harrison J M (1978) The control of responding by au-ditory stimuli Interactions between dimensions of stimuli Journal ofthe Experimental Analysis of Behavior 30 97-106

Sturdy C B Phillmore L S Price J L amp Weisman R G (1999)Song-note discriminations in zebra finches (Taeniopygia guttata)Categories and pseudocategories Journal of Comparative Psychol-ogy 113 204-212

Vaughan W Jr amp Greene S L (1984) Pigeon visual memory ca-pacity Journal of Experimental Psychology Animal Behavior Processes10 256-271

Watanabe S amp Sato K (1999) Discriminative stimulus propertiesof music in Java sparrows Behavioural Processes 47 53-57

APPENDIX Music Bibliography

ClassicalJohan Sebastian Bach 3 Oboe Concertos BWV 1053 1055 and 1059

Philips 412851-2 G F Handel Trio Sonatas Denon 38C37-7026 Wolfgang Amadeus Mozart amp Giuseppe Ferlendis Oboe Concertos

Philips 420 179-2Ludwig van Beethoven The Sonatas for Piano amp Cello CBS M2K

42446Antonio Vivaldi 3 Cello Concertos amp Sonatas Decca Record Co 433

052-2Antonio Vivaldi Guitar Concertos Philips 412 624-2Franz Schubert Trout Grammophon 413-453-2Baroque Favourites Naxos 8550102Johan Sebastian Bach Brandenburg Concertos 1ndash3 MCA Classics

MCAD-5956Johan Sebastian Bach amp Antonio Vivaldi Concerti for 2 Violins CBS

MK 37278Maurice Andre Baroque en Famille EMI 5-55488-2J S Bach C P E Bach J C F Bach amp W F Bach Trio Sonatas CBS

MK-37813

BluesJohn Lee Hooker Blues Before Sunrise Masters CLCD 61028-2John Lee Hooker The Real Folks Blues Chess CHD-9271 MCA (Ex-

cluded Track 9)John Lee Hooker Boom Boom K-TEL 3676-2 Muddy Waters Irsquom Ready CBS ZK 34928Koko Taylor I Got What It Takes ALCD 4706The Best of Chess Blues Volume 2 Chess CHD-31316 MCAThe BluesmdashVolume 3 Chess CHD-9276 MCABlending the Blues MCA MSD-36021 (Excluded Tracks 9 11 amp 14)Legendary Blues Volume 1 Blues Journey SS1896Sonny Boy Williamson The Real Folk Blues Chess CHD-9272 MCAEssential Blues 2 House of Blues (2 CDs) Platinum Entertainment Inc

514161183 2The Blues Story Masters MCAD 61056-2

(Manuscript received May 11 2001 revision accepted for publication August 3 2001)