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Journal of Comparative an d Physiological Psychology1965, Vol.
59, No. 2, 298-300ACQUISITION OF SIDMAN AVOIDANCE RESPONDING AS
AFUNCTION OF S-S INTERVAL
RUSSELL C. LEAF1
Squibb Institute fo r Medical ResearchProcedures for producing
rapid and reliable lever-press Sidman avoidanceacquisition in 100%
of an unselected group of rats are described. Groups of12 rats were
exposed to schedules with an R-S interval of 20 sec., at S-S
in-tervals of 1, 3, 5, 10, and 20 sec., with a constant power
shocker. 1st sessionresponse levels were a monotonically decreasing
.function of S-S interval.The hypothesis that acquisition
probability is due to reduction of shockfrequency was supported,
but acquisition levels of responses with spacedIRTs were unrelated
to S-S intervals.
Although many experiments have replicatedSidman's (1953) finding
that rats can be trainedto perform avoidance responses without
extero-ceptive warning stimuli, little parametric in-formation on
Sidman avoidance acquisitionhas been reported. This lack is
probably due tothe fact that methods for producing
reliablelever-pressing Sidman avoidance learning inall Ss, from an
unselected group of rats, are notreadily available. The Es who have
trainedlarge groups of & have sometimes CVVeissman,1962)
reported a large percentage of trainingfailures, even when the
behavior was: studiedfor many training sessions.The present paper
reports procedures forproducing reliable and rapid acquisition
ofSidman avoidance responding in a single ex-perimental session.
The shock-shock (S-S)interval was systematically varied in order
toobtain data on the role of shock density reduc-tion in Sidman
avoidance acquisition. The onlyunusual feature of the training
conditions wasthe use of a relatively constant power
source(Campbell & Teghtsoonian, 1958; Hill, Fla-nary,
Kornetsky, & Wikler, 1962), rather thanconstant current, shock
source.
M E T H O DSubjects
The Ss were 40, 250-300 gm, male and 20, 200-250 gm . female
albino rats purchased from CammResearch Institute, Wayne, New
Jersey.Apparatus
The experimental space was a modified LehighValley Electronics
No. 1316 chamber, 7% X 12 X .8 in. It had two LVE 1352 levers
mounted sym-metrically on one 8 in. wall. The centers of the
1Stanley A. Muller provided assistance inanalysis of data, and
Peter L. Carlton commentedon preliminary manuscript drafts of the
workdescribed.
levers were 1 V 4 in . above the grid floor of thechamber, and
were 5 in. apart. The chamber, in anLVE 1316 C sound insulated
cubicle, was placedin a room separate from automatic programingand
recording equipment. The chamber blower fa nand a masking white
noise served to minimize theeffects of extraneous stimuli.The shock
source was a modified LVE 1311shocker. It consisted of (a) a
step-up isolationtransformer adjusted so that the voltage in
itssecondary coil was 725-v. ac, ( t > ) a 10 0 K ohmshunt
across this secondary, (c) a 136 K ohm re-sistance in series with
it, (d ) an oil-immersed gridscrambler, (e) 40-ft. parallel
wire-grid cable, (/)grid, and (g) S. This arrangement produced
about60 v. maximum across S, measured on a cathode-ray oscilloscope
(Tektronix Model 555), at rela-tively constant power, after
attenuation by thecapacitative reactance of scrambler, cables,
andgrid.Procedure
Each S was given one 6-hr, acquisition session.The naive S was
placed in a darkened experi-mental chamber. After 10 min., a 20-v.
GeneralElectric 304 house light was turned on, and theexperimental
contingencies started. The response-shock (R-S) interval was 20
sec. and shock dura-tion 0.3 sec. for all Ss. Lever presses did not
altershock duration. A small pilot light mounted aboveeach lever
was illuminated for 40 msec, each timethe lever was depressed.
Avoidance contingencieswere programed on only one lever for each S.
Theright lever was ,the avoidance lever for half themale and half
the female Ss, and the left leverwas the avoidance lever for the
remaining /Ss.The Ss were ran in 12 replications of 5 Ss.Each
replication contained only male, or onlyfemale, Ss. Within a
replication, Ss were randomlyassigned to order of training and to
one of fiveS-S intervals, 1, 3, 5, 10, and 20 sec.
RESULTSAll /Ss in the 1- and 3-sec. S-S interval groupsand 11
/Ss in the 5-sec. group learned to avoidreliably, but only 4 /Ss in
the 10-sec. and 1 S
298
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SUPPLEMENTARY REPORTS 299
R a n g e \ Interquart i leJ R a n e e M e a n
A V O I D A N C E L E V E RT O T A L S H O C K S
20 3" 5" 10"S - S Interval|" 3" 5" 10"S -S IntervalFIG. 1.
Means, interquartile ranges, an d ranges of relevant lever
responses, an d total shocks fo rexperimental groups with
acquisition S-S intervals of 1, 3, 5, 10, and 20 sec.
in the 20-sec. group did so. The reliable Ss allmade at least
1,000 responses on the avoidancelever, spent less than 50% of the
time in S-Sintervals, and showed steady rates of avoid-ance
responding during the last hour of thesession, as judged from
cumulative records.None of the & that failed to learn
reliablyhad steady terminal rates, and all of these Ssspent more
than 50% of the session in the S-Sintervals and made fewer than
1,000 responseson the avoidance lever.The effect of the S-S
interval on avoidancelever responding is shown in Figure 1.
Avoid-ance responding was a significant (H 28.1,d f = 4, p <
.001) monotonic decreasing func-tion of S-S interval. As Figure 2
shows, how-ever, this monotonic function was due pri-marily to the
levels of (a) rapid burst-likeresponses with interresponse times
(IRTs)less than 2 see., and (6) responses that oc-curred after the
receipt of an R-S shock(IRTs > 20 sec.). High levels of spaced
re-sponses, with IRTs of 2-20 sec., were observed;but these levels
were not monotonically re-lated to S-S interval. Each of the nine
classintervals of 2 sec. for IRTs from 2-20 sec.showed an inverted
U-shaped function relatingresponse level to S-S interval, with
peaks ateither 3 or 5 sec. All nine functions weresignificant (H
> 18.5, df = 4, p < .001 for eachdistribution).
In order to assess the effect of S-S interval,additional
analysis was carried out on the dataof only those < S s that
learned reliably (1,000responses, 50% S-S time, steady terminal
rates)
and were trained with 1, 3, and 5 sec. S-Sintervals. These &
showed no significant rela-tionship between avoidance responding
andS-S interval (H = 0.6, df - 2, p > .50). Whenavoidance
responses were categorized by IRTs,as shown in Figure 2, 0-2 sec.
IRT responseswere a nonsignificant decreasing function ofS-S
interval (H = 2.0, df - 2, p > .20), 2-20
RELEVANT LEVER IRT DISTRIBUTIONS
2142193017001600150014001300
U > 12001100g 10002 900K 800
700600500400300200100
0
; [
O '( 3
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1
r 1 i o n SS ' "3 " 5" 10" 20
cot
1
[
Means
InterquartileRangeRange
1AH
^
1 1
1
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IT 5" 10- 20- 1"3"5" 10" Iff 1'3"5- 10" 20-2"IRTS 2"-20"IRTS.
>20" IRTS
FIG. 2 . Interresponse time distributions for Sswith acquisition
S-S intervals of 1, 3, 5, 10, and20 sec. (Means, interquartile
ranges, and ranges ofthe frequency of responses with IRTs of 0-2
sec.,2-20 sec., and greater than 20 see. are shown foreach S-S
interval.)
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300 SUPPLEMENTARY REPORTSs e c . IRT responses were a
nonsignificant in-creasing function of S-S interval (H = 1.5,dj =
2, p > .30), and IRTs greater than 20s e c . were a significant
monotonic decreasingfunction of S-S interval (H = 10.8, df - 2,p
< .01). Thus, the number of avoidance leverpresses per shock
delivered was an increasingfunction of S-S interval over the range
from1-5 sec. The 5-sec. Ss responded almost as oftenas the 1-sec.
Ss, but received many fewershocks.The effect of S-S interval on
total shockswas nonmonotonic, but significant (H = 20.6,d f = 4, p
< .001). As Figure 1 indicates, thesignificance of this function
was partly due tothe restriction on the maximum total shocks in6
hr. imposed on S s with S-S intervals of 10and 20 sec.Responding on
the irrelevant lever was in-frequent for all S-S interval groups
(all meansless than 400 responses). Most irrelevant re -sponding
occurred early in the session beforeavoidance response rates were
stable.The observed behavior of all Ss in responseto shock
consisted of jumping and runningmovements. Every /S was observed
for at least20 successive shock presentations, and no in-stances of
crouching or freezing during shockwere ever observed. These
observations oftencovered as many as 100 successive shocks,and were
made at randomly selected timeperiods during experimental
sessions.
DISCUSSIONThe major findings of this experiment are (a)that
reliable acquisition of Sidman avoidancelever pressing can be
produced in 100% of anunselected group of rats under
appropriatetraining conditions; (6) that first session re-sponse
levels are a monotonically decreasingfunction of acquisition S-S
interval; and (c )that the first session frequency of responseswith
IRTs of intermediate latency is an in-verted U-shaped function of
acquisition S-Sinterval.These data confirm Sidman's (1962)
impres-sion that acquisition during early exposure toavoidance
contingencies is best at brief S-Sintervals. The monotonic function
observed isalso consistent with Black and Morse's (1961)findings,
with dogs in a shuttle box, that Sid-man avoidance acquisition
improved as S-Sintervals approached escape contingencies (0-s e c .
S- S interval).At the 1-, 3-, and 5-sec. intervals, under
conditions which all produced good acquisition,no significant
relationship was found betweenS-S interval and responses with IRTs
that werebriefer than the R-S interval. This finding isconsistent
with previous data (Anger, 1963)from well-trained animals, and is
consistentwith evidence that the major determinant ofSidman
avoidance IRT distributions is the R-Srather than S-S interval. The
nonsignificantdecreasing level of responses with 0-2 sec.IRTs
across S-S intervals of 1-5 sec. is prob-ably due to the fact that
repetitive respondingafter shock consists almost entirely of
re-sponses with brief IRTs. The nonsignificantincreasing level of
responses with IRTs of 2-20s e c . across S-S intervals of 1-5 sec.
is theascending limb of the significant invertedU -shaped function
relating such responses to S-Sintervals over the whole 1-20 sec.
range. Theconsistent appearance of an ascending limb,as part of an
inverted U-shaped function, atevery intermediate 2-sec. IRT
category from2-20 sec. deserves attention, even though be-tween
group differences of Ss trained at S-Sintervals of 1-5 sec. were
not significant. Itappears from these data that the conditionwith
the longest S-S interval among severalhighly effective training
conditions is the "best"Sidman avoidance training condition,
fromthe standpoint of responses performed pershock delivered.
REFERENCESA N G E R , D. The role of temporal discriminations
inthe reinforcement of Sidman avoidance be-havior. J. exp. Anal.
Behav., 1963, 6, 477-506.B L A C K , A. H., & M O U S E , P.
Avoidance learning indogs without a warning stimulus. J. exp.Anal.
Behav., 1961, 4,17-23.C A M P B E L L , B. A., & T B G H T S O
O N I A N , R . Electrical
and behavioral effects of different types ofshock stimuli on the
rat. J. comp. physiol.Psychol, 1958, 51, 185-192.HILL , H. E. , F L
A N A R Y , H. G. , KORNETSKT, C. H.,& W I K L E R , A.
Relationship of electrically in-duced pain to the amperage an d
wattage ofshock stimuli. /. din. Investig., 1962, 31,464-472.S I D
M A N , M . Avoidance conditioning with briefshock and no
exteroceptive warning signal.Science, 1953, 118,157-158.S I D M A N
, M. Reduction of shock frequency as rein-forcement fo r avoidance
behavior. J. exp.Anal. Behav., 1962, 5, 247-257.W E I S S M A N ,
A. Nondiscriminated avoidance be -havior in a large sample of rats.
Psychol. Rep.,1 9 6 2 , 10, 591-600.
(Received May 25, 1964)
