Blatchford&Foulkes

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The International

Journal ofSpeech,Languageand the Law

doi : 10.1558/ijsll.2006.13.2.241

Article

Identi cation of voices in shouting

Helen Blatchford and Paul Foulkes

AbstractTwo experiments were carried out to assess the ability of lay listeners to identify familiar voices from shouted samples. e experiments were conducted a er a murdercase in which a witness claimed to recognise the voice of a masked gunman based ontwo shouted words: get him! Our experiments were designed to explore the extent towhich a listener can identify a known voice from a shouted sample, and also whethera two word sample is su fficient for identi cation. Recordings were obtained from a group of nine females who formed a close social network, plus six foils. Two shoutedutterances were extracted for listening tests: for Test 1, get him! , and for Test 2, facedown on the ground and hands behind your back now! irteen listeners from thesame social network participated in the tests. Listeners correctly identi ed familiarspeakers in 52% of cases in Test 1 and 81% in Test 2. ere was considerable variationin results across listeners, and also with respect to individual voices. e results suggestthat recognition of shouted voices is far from perfect , even in closed tests carried outamong a close network. e variability in performance emphasises the need to subjecta witnesss ability to identify a voice in a forensic case to formal testing wherever this

is feasible. K : , , ,

Affi liationsHelen Blatchford: City University, London

Paul Foulkes: J. P. French Associates and University of York

Correspondence: Paul Foulkes, Department of Language and Linguistic Science, University of York, York YO105DD, UK

email: [email protected]

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Introduction

In 2003 two young women, Letisha Shakespeare and Charlene Ellis, were shotand killed in a drive-by shooting in Birmingham, UK. e incident was appar-ently gang-related, although the women were not the intended victims. e carfrom which the shots were red continued along the road, and further shotswere red at Leon Harris, who at the time was sitting in a parked car. Harrisgot out of the car and ran away. As he did so the masked gunman shouted gethim! Harris gave a description of the characteristics of the voice and namedTafarwa Beckford as the perpetrator. e two had spent time together in ayoung off enders institution some time previously, but that appears to have

been their only form of contact.J. P. French Associates were subsequently engaged by Beckfords defenceteam to produce a report on Harriss evidence (French and Harrison 2005).Analysis was undertaken to assess whether Harriss description was a goodmatch for Beckfords voice. Tests were also made of the reliability of theidenti cation given Harriss fairly limited experience of Beckfords voice, andthe fact that it was made on the basis of only two shouted words. EventuallyHarriss evidence was withdrawn by the prosecution. Following problems withother evidence against Beckford the jury were instructed to return a verdictof not guilty for him.

e experiments we report in this article were carried out to explore someof the key issues in the Beckford case in a more general context. Our aim wasto provide further evidence on the reliability of witness identi cation of voiceswhen hearing short and shouted samples. We begin with a brief summary ofprevious research on speaker identi cation by lay listeners, focusing on theeff ects of familiarity with the speaker, sample length, and shouted stimuli. Wethen describe the experiments we performed, before nally drawing conclu-

sions on the forensic implications of our results.

Speaker identi cation by lay listeners

Speaker identication is a task performed as a matter of routine, for examplewhen answering the telephone or hearing voices outside ones o ffice. However,it is a well known fact, at least among linguists, that the task of identifying afamiliar voice is not always performed successfully. When answering the phone,for example, we may fail to recognise the voice of someone we know, we may

mistakenly believe we recognise the voice of a stranger, or we may attribute afamiliar voice to someone else we know rather than to the actual speaker.It is of great forensic importance that we should understand how reliable

listeners are at speaker identi cation, and that we isolate the factors whichhave an impact on the identi cation process, in order that courts can assess


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evidence such as that described in the Beckford case earlier. Evidence suggeststhat lay-people thus potential jurors overestimate the ability of listeners

to identify familiar voices and to reject unfamiliar ones (Yarmey et al . 2001,Yarmey 2004). In reality everyone makes mistakes from time to time, for anumber of reasons (reviewed by Bull and Cli ff ord 1984). Contributory factorsto variation in performance include the age and hearing ability of the listener,the length of delay between initial exposure to a voice and the identi cationtask, the nature and extent of any disguise in the voice sample, and the degreeto which the listener is familiar with the voice. e two factors of particularrelevance here are the duration and nature of the sample upon which identica-tion is performed.

With respect to duration, there is some debate as to whether identi ca-tion rates correlate with length of the stimulus. Bull and Cli ff ord (1984: 108)conclude that duration is not particularly important provided that at least onesentence is presented. Studies which have used long samples report relativelyhigh rates of successful identi cation of familiar voices. In a closed identi ca-tion task using samples of 2.5 minutes, for example, Hollien et al . (1982) foundthat a group of ten listeners identied familiar voices in 98% of cases. Far lowerrates have been reported when very short stimuli have been used. For example,

Ladefoged and Ladefoged (1980) report a success rate of 31% in a test using thesingle wordhello, in which Peter Ladefoged (in)famously failed to recognise hisown mother. Varied sample lengths of similar sounding voices were used in aset of tests by Rose and Duncan (1995). eir results support the conclusiondrawn by Bull and Cliff ord (1984). When the stimuli consisted of hello, cor-rect identi cation averaged 57%. Identi cation rates were 85% when stimulicontained either a four word sentence or 45 seconds of speech.

Identication rates are further aff ected by the nature of the sample, includingits specic content, the medium of transmission, and whether it consisted ofmodal or non-modal speech. Yarmey (2004) carried out a series of closedtests using four speakers. He found that short samples consisting of linguisticmaterial elicited higher rates of identi cation than non-linguistic ones such aslaughter, coughing or moaning. Several studies, including Rose and Duncan(1995) and Foulkes and Barron (2000), have noted that listeners are able toidentify some voices more readily than others in the same test. is suggeststhat listeners attend to salient acoustic or linguistic cues in the samples such asreexes of voice quality or regional accent. e medium of transmission has

also been shown to aff ect identi cation. In particular, transmission through atelephone results in lower performance levels compared with tests using speechthat has been recorded under optimal conditions (Rathborn et al . 1981). In astudy with an open task and nine second samples of telephone speech, Foulkesand Barron (2000) found identi cation rates to average 68%.


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Finally, rather little research has been carried out on the accuracy of speakeridenti cation when the sample of speech is shouted. While this was not a

central concern in the study by Yarmey (2004), it is noteworthy that his par-ticipants scored 47% with the shouted utterance help me! compared with 68%for hello spoken normally. However, it has been established that the acousticcharacteristics of shouting diff er systematically in a number of ways from thoseof normal speech (Rostolland 1982, 1985, Traunmller and Erickson 2000).For example, segmental durations, formant values and suprasegmental featuresare all aff ected by a change from modal speech to shouting. In short, therefore,shouting is not simply loud speech. It has been suggested that shouted voicesare less discriminable due to increased uniformity in f0 compared with modalspeech (Rostolland 1982). We can therefore also hypothesise that listenerswho are familiar with a particular voice might not be as accurate in identify-ing that voice when they hear it in a di ff erent mode of vocal e ff ort such asshouting. Support for this hypothesis is provided by Brungart et al . (2001).

ey trained listeners to identify eight previously unfamiliar voices, four maleand four female, in three modes of speech: normal conversation, whisper andshouting. When listeners heard test stimuli in the same mode as the trainingstimuli, correct identi cations were high (90%-86% for conversational speech,

87%-95% for shouting, 6967% for whisper; the

rst

gure in each case formale talkers and the second for females). Identi cation rates were far lowerwhen the test stimuli were in a di ff erent mode from that used in training. Forexample, when shouted stimuli were given to listeners who had been trainedwith conversational material, identi cation rates dropped to 70% for maletalkers and 43% for females.

In summary, previous research has shown that short samples can pose aserious problem for speaker identi cation. Less clear is the eff ect of shoutedsamples, but the available evidence also indicates that shouting may impairlistener performance. We turn now to our own experimental investigation. Inlight of the evidence in the Beckford case, the main issue to be addressed wasthe accuracy of speaker identi cation by lay listeners when presented withshort, shouted samples of familiar voices.

Experimental design

Participants

Previous studies have shown that degree of familiarity aff ects listener perform-ance in identi cation tasks (e.g. Hollien et al . 1982). All things being equal,the more familiar the voice the better the identi cation rate. Some studieshave controlled for this factor by training listeners to identify a set of voices


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which were, prior to the test, unfamiliar. However, while this strategy gains incomparability across listeners, it loses in terms of the naturalness of the task. We

therefore elected to recruit a pre-existing group of participants to act as speakersand listeners. e group, henceforth referred to as the network, consisted of14 (nine female, ve male) nal-year undergraduate students of French at theUniversity of York. is network, which included therst author, comprised theentire cohort for their year. At the time of the experiment the network membershad known each other for three and half years. ey had studied as a group forat least four hours a week for the duration of their acquaintance. ey had alsoformed close social bonds, with all members of the group having had extensivesocial interaction with all other members. All were native British Englishspeakers, from a variety of regional backgrounds. None reported any historyof speech or hearing problems. Most had studied linguistics and phonetics aspart of their degrees but none (apart from the rst author) had specialised insubjects directly relevant to the task at hand.

Naturally the social contacts between some members were stronger thanothers, but all appeared much more rmly established than that between LeonHarris and Tafarwa Beckford. We were therefore con dent that our networkmembers could justi ably be described as having a high degree of familiarity

with each others voices.

Speakers

e nine female members of the network were asked to provide materials tobe used in the listening tests. Six female foils were also recruited who wereunknown to any of the participants other than the rst author. e foils wereall native English speakers, and included two Americans.

Listeners

irteen participants undertook the listening tests: eight of the nine womenwho had acted as shouters, and the ve male members of the network. eonly network member who did not participate, for obvious reasons, was therst author.

Voice samples

All voice samples were recorded in a sound-proof studio with a Neuman V87microphone and Adobe Audition so ware at a sample rate of 44.1 kHz. espeakers were rst asked to read aloud both a short text and a list of sentences,three times and in a normal voice. e sentences included get him! , the phrase


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used in the Beckford case, and a number of longer items. All sentences wereconstructed to be feasible in a criminal context. e act of reading at a normal

level was designed to enable the speakers to get accustomed to the materialsand to the setting of the recording laboratory. ey were then asked to shoutthe sentences as loudly as possible, standing approximately one metre awayfrom the microphone.

Some participants showed understandable reluctance to shout on cue (anda seventh potential foil in fact refused to do so, withdrawing from the experi-ment). ey were therefore asked to repeat the exercise until the administratorswere happy that the shouts were of a reasonably natural amplitude. Successfulelicitation was aided by the fact that most participants were close friends of therst author, who in some cases demonstrated the appropriate level of shoutingin order to help participants lose their inhibitions. e material eventuallyobtained undoubtedly varied across participants in terms of vocal e ff ort, butwe were satised that all materials could be classi ed as genuine shouts.

Sound levels were monitored during the practice shouts in order to set therecording levels as high as possible without circuit overload. Once the recordinglevels had been adjusted participants were recorded shouting each sentencethree times.

Listening tests

Sections of the recordings were extracted for use as stimuli in two listening tests.e original .wav soundles were edited using Audacity 1.2.4 soware. For Test

1, tokens of the phrase get him! were extracted. Test 2 was designed to assess theeff ect of a longer sample for comparison. e twelve syllable item face down onthe ground and hands behind your back now! was chosen for this purpose. Foreach test 39 tokens were obtained: three each from the nine network membersand two each from the six foils.

Stimuli were not normalised further for amplitude, on the reasoning that variability in the level of shouting might have served as a cue to speaker identity.However, exploratory analysis of responses to the stimuli with highest andlowest amplitude revealed no distinct patterns. Given the limited sample ofstimuli and number of voices available in these experiments, we elected not toconsider relative amplitude any further.

For presentation to listeners the stimuli were compiled into a PowerPointle.

e use of PowerPoint allowed them to be played automatically, supported by visual information on the structure of the test and the identi cation numberof the stimulus being heard. e playback order was random, except that noadjacent pair was taken from the same speaker. A delay of eight seconds was


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inserted between each stimulus. A set of six stimuli was also used to provide apractice run before listeners participated in the main tests. Listeners were given

an answer sheet containing the nine names of the possible shouters. ey werealso off ered two other choices: unknown to indicate an unfamiliar speaker,and dont know. e nature of the task was explained at the beginning of thePowerPoint presentation. Listeners participated individually in the tests via aDell Inspiron 510m laptop and Sony MDR-V250 headphones in a quiet room.Test 1 was administered three weeks a er the recordings were made, and Test 2was carried out two weeks a er Test 1.

e tests were therefore closed, which marks a departure from the forensicscenario in which Leon Harris found himself. However, the nature of thenetwork meant that members of the group were aware that others were par-ticipating in the recordings and it was therefore not practicable to constructan open test.

Results

A summary of the results is provided in Table 1. Further details are given inthe discussion that follows.

Table 1 Summary of results

Familiar shouters Foils

Syllables Correct % Range forlisteners

Range forvoices

% rejected % falsepositives

Test 1 2 52 2296% 1983% 27 45

Test 2 12 81 48100% 31100% 64 19

Test 1: get him!

As indicated in Table 1, the overall proportion of correct responses to familiar voices was 52% in Test 1. ere was, however, considerable variation acrosslisteners. e results for the 13 individual listeners are given in Figure 1. eshaded bar to the right represents the overall mean. e results for eleven of the

listeners were close to the overall mean, at c. 4060%. One listener, A, registeredan almost perfect performance, with just one error for the 27 stimuli. ListenerF, on the other hand, scored only 22% (6/27).


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Figure 1 Results for individual listeners, Test 1 (n = 27 per listener, total N = 348).

Results also varied for individual voices. Figure 2 shows the relative proportionof correct responses for each voice, with responses from all listeners pooled(black bars). Also shown are the proportion of false positives (i.e. incorrect

naming of another network member) and the proportion of dont knowresponses. e rightmost bar represents the mean scores for all listeners. It isapparent that the voices can be split into two groups. Voices 15 were identiedmore accurately than voices 69. Correct responses for voices 15 were at least60%, and as high as 83%, while voices 69 were identied in at most 33% ofcases. False positives and dont know answers were thus also higher for thelatter group. Across all nine voices 33% of the responses were false positives.

Figure 2 Results for individual voices, Test 1 (n = 42 per voice, total N = 348).

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Foils were rejected in only 27% of cases. e best performance by a listenerwas to reject 75% of foils (9/12). One particular foil was rejected much more

frequently (61%) than the other ve (732%). Almost half the foils (45%)were incorrectly attributed to network members. e two American foils were

misidenti ed just as frequently as the British foils, and of particular note is thefact that one foil was incorrectly identi ed as the same network member noless than 15 times.

Test 2: Face down on the ground and hands behind your back now !

e performance of listeners improved markedly in Test 2, in which they heardthe longer samples. Correct identi cations rose to 81% compared to the 52%found in Test 1. Figure 3 shows the results for all listeners individually (blackbars). e scores from Test 1 are repeated for the sake of comparison (grey bars).It can be observed that 11 of the 13 listeners made a higher number of correctidenti cations in Test 2. e exceptions to this were A (the best performer intest 1) and L, but the performance of these two did not fall signi cantly. Sixlisteners showed a statistically signi cant improvement in performance, asindicated by asterisks (comparisons made with chi square tests). Variation

across listeners was again observed, however. One listener, C, attained 100%correct identications, eight managed scores over 80%, but the worst perform-ance (L) was 48%.

Figure 3 Results for individual listeners, Tests 1 and 2 (n = 27 per listener, total N = 348;signicant diff erences across tests: * p < .05, ** p < .01).

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Figure 4 illustrates responses to the nine familiar voices. For this test we canobserve that seven of the voices were handled well by listeners. Two voices (2

and 5) were correctly identi ed in all instances. Scores for voices 8 and 9 weremarkedly lower than those for the rest of the network. False positives accountedfor 15% of responses overall.

Figure 4 Results for individual voices, Test 2 (n = 42 per voice, total N = 348).

e rejection rate for foils showed a substantial increase in Test 2, to 64%,with 19% false positives. One listener managed to reject all foil stimuli. eAmerican foils were this time the most consistently rejected (89% and 93%compared with 1871% for the others).

Discussion

e proportion of correct identi cations of familiar voices in Test 1, 52%, waswell above chance (11%, given that there were nine candidates), and closelycomparable to the results reported in similar studies where short and/orshouted stimuli were used (e.g. Rose and Duncan 1995, Yarmey 2004). Resultsfor Test 2 were predictably better. Again, the proportion of correct responseswas comparable to that reported in similar studies (e.g. Bull and Cli ff ord 1984,Rose and Duncan 1995). e longer samples presumably provided listenerswith more material to process in order to make their decisions. e diff erencein duration enabled several listeners to register signi cant improvements intheir performance with familiar voices, and also led to a far higher rejectionrate for foils.

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To focus solely on mean scores in the tests, however, is to underplay the com-plexity apparent in the ndings. e results suggest that robust identi cation

can be made on the basis of short, shouted samples, but successful identicationdepends very much on both the listener and the voice. Even in Test 1, wherethe material presented was simply get him! , one listener managed to identifythe shouters in all but one case. In Test 2 one listener scored perfectly and threeothers made only one or two errors with 27 stimuli. Two voices in Test 2 werecorrectly identi ed in all instances by all listeners.

Two particular factors can be isolated which may contribute to the variationin results. First, we should recall that although participants were undoubtedlyfamiliar with each others voices, the degree of familiarity was inevitably vari-able across the network. It could be observed informally that the best performerin Test 1 was a particularly prominent member of the network who, by her ownaccount, based her social life around the group. e best recognised voicesalso belonged to particularly popular members of the network, while the two voices which proved most difficult to identify (8 and 9 in Test 2) were those ofrelatively peripheral group members. Degree of familiarity might therefore beof relevance in assessing listener performance, as other studies have concluded(e.g. Hollien et al . 1982).

A second important factor in explaining the results is the relative salienceof individual features in the voices tested. e better recognised voices werethose which contained marked sociolinguistic or regional features relative tothe rest of the group (cf. Rose and Duncan 1995, Foulkes and Barron 2000).

e participant who was most frequently identi ed in both tests was originallyfrom Liverpool, a city renowned for its distinctive accent (Wells 1982). Shehad a very noticeable regional accent compared with the other participants. InTest 2 the other voice identied accurately in 100% of cases contained a stronglylabiodental realisation of /r/, apparent in the word ground , which is an emergent variant in many dialects in England (Foulkes and Docherty 2000). Note alsothat the American foils were consistently rejected in Test 2.

Concluding comments

e experiments described here were designed to explore the accuracy andreliability of listeners in identifying familiar voices from shouted samples.As expected, the short duration and non-modal nature of the stimuli createdproblems for a group of listeners who knew each other well, although thesamples did not present an insurmountable obstacle to listeners. However, anoverall rate of 52% in Test 1 is of course well below the level of reliability thatcould reasonably be tolerated by a court in a case, like that against Beckford,where identi cation evidence of this type is central. Even the correct rate of


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81% in Test 2 surely still falls below a judicially acceptable level (cf. Knzel1994, Rose and Duncan 1995). Familiarity with a voice in everyday interaction

therefore does not guarantee successful identi cation of that voice when it isheard shouting.Although the experiments were conducted in light of the Beckford case, we

refrain from making direct comment on the evidence which was to be givenby Leon Harris since there are potentially signi cant diff erences between thetasks carried out in our listening tests and the identication made in the originalincident.

First, we cannot accurately assess how much variation there was in degree offamiliarity with the voices concerned. However, our participants certainly kneweach other well, and from what is known about the relationship between Harrisand Beckford it is likely that our network members had had considerably longerand richer experience of each others voices than Harris had of Beckfords.

Secondly, our results indicated that there was substantial variation in howwell individual voices were identi ed. Some voices were identi ed more accu-rately and more consistently than others, which in part may be due to thespecic acoustic, phonetic and linguistic characteristics of the voice concerned.It remains a moot point whether the salience of certain characteristics is a

relative phenomenon i.e. some features may make a voice stand out rela-tive to others in a particular community of speakers or whether there arefeatures which have universal salience to listeners. Either way, we cannot besure whether Harris wouldnd Beckfords voice more or less easily identiablethan any other. (Harris did in fact claim that the assailants voice was distinc-tive, and described a number of features of the voice which underpinnedhis identi cation of Beckford, but the investigation by French and Harrison(2005) raised questions about the distinctiveness of these features relative toBeckfords peer group.)

irdly, our experiments also showed considerable variation in the ability oflisteners to perform the task. Some did very well, even with the stimulus gethim! On the other hand, even with the longer sample in Test 2 one participantstill identied fewer than half of the voices.

Previous research on voice identi cation has highlighted the range of factorsthat can aff ect performance. Although we also set out to investigate some ofthese factors, in terms of varied duration and the use of shouting, we considerthat the most important nding from the forensic perspective is the variation

in the results. Listeners displayed highly divergent abilities to perform theidenti cation tasks. Furthermore, some voices proved easier to identify thanothers. Such variation means that the ability of a witness to identify a voicecannot be taken on trust.


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Naturally, caution must be exercised when extrapolating the results of acontrolled experiment using a closed test in ideal listening conditions to a real

forensic situation. Harris heard his assailants voice in a street and under whatmust have been highly stressful circumstances. e chances of his correctlyidentifying his assailant under those conditions cannot be predicted directly onthe basis of experimental data. e variation inherent in our results would allowus only to predict a listeners ability in an identi cation task within a relativelybroad range. is emphasises the need to subject a witnesss ability to identifya voice to formal testing whenever it is feasible to do so, particularly when thesample at issue was short or shouted.

Acknowledgements

Versions of this material were presented at the 2005 IAFPA conferencein Marrakech, the 2006 BAAP colloquium in Edinburgh, and the 2006Sociolinguistics Symposium in Limerick. We are grateful to colleagues at thosemeetings, as well as two reviewers, for their comments. We also record our thanksto Peter French and Philip Harrison for sharing their data and report concerningthe Beckford case, and to Huw Llewellyn-Jones for technical assistance.

References

Bull, R. and Cliff ord, B. R. (1984) Earwitness voice recognition accuracy, in G. L. Wellsand E. F. Lo us (eds) Eyewitness Testimony : Psychological Perspectives. Cambridge:Cambridge University Press, 92123.

Brungart, D. S., Scott, K. R. and Simpson, B. D. (2001) e inuence of vocal eff ort onhuman speaker identi cation, Eurospeech, 2001: 74750.

Foulkes, P. and Barron, A. (2000) Telephone speaker recognition amongst members of a

close social network, Forensic Linguistics: e International Journal of Speech, Languageand the Law, 7: 18198.

Foulkes, P. and Docherty, G. J. (2000) Another chapter in the story of /r/: labiodental variants in British English, Journal of Sociolinguistics, 4: 3059.

French, P. and Harrison, P. T. (2005) Lay-witness voice description and identi cation:consideration of shouting, pitch and accent, paper presented at paper presented at theIAFPA conference, Marrakech, Morocco.

Hollien, H., Majewski, W. and Doherty, E. T. (1982) Perceptual identi cation of voicesunder normal, stress, and disguise speaking conditions, Journal of Phonetics, 10:13948.

Knzel, H. (1994) On the problem of speaker identi cation by victims and witnesses,Forensic Linguistics: e International Journal of Speech, Language and the Law, 1:4558.


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Ladefoged, P. and Ladefoged, J. (1980) e ability of listeners to identify voices, UCLAWorking Papers in Phonetics , 49: 4351.

Rathborn, H., Bull, R. and Cliff ord, B. R. (1981) Voice recognition over the telephone, Journal of Police Science and Administration, 9: 28084.

Rose, P. and Duncan, S. (1995) Naive auditory identi cation and discrimination of simi-lar voices by familiar listeners, Forensic Linguistics: e International Journal of Speech, Language and the Law, 2: 117.

Rostolland, D. (1982) Acoustic features of shouted voice, Acustica, 50: 11825.

Rostolland, D. (1985) Intelligibility of shouted voice, Acustica, 57: 10321.

Traunmller, H. and Erickson, A. (2000) Acoustic e ff ects of variation in vocal eff ort bymen, women, and children, Journal of the Acoustical Society of America, 107: 334851.

Yarmey, A. D. (2004) Common-sense beliefs, recognition and the identi cation of famil-iar and unfamiliar speakers from verbal and non-linguistic vocalizations, International Journal of Speech, Language and the Law, 11: 26777.

Yarmey, A. D., Yarmey, A. L., Yarmey, M. J. and Parliament, L. (2001) Commonsensebeliefs and the identi cation of familiar voices, Applied Cognitive Psychology , 15:28399.

Wells, J. C. (1982) Accents of English. (3 vols.) Cambridge: Cambridge University Press.

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