Proceedings Fonetik 2009 - Institutionen för lingvistik

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Proceedings, FONETIK 2009, Dept. of Linguistics, Stockholm UniversityFalse Acceptances / Foil in Target Absent (TA) and TargetPresent (TP)Nr302520151050JL MM TN KG CF JÅ MS JL MM TN KG CF JÅTA TA TA TA TA TA TA TP TP TP TP TP TPFigurant7-8 y11-12 yAdultsAllFigure 1. False acceptances for each figurant speaker in the 3 age groups and the sum (all) for bothtarget absent (TA) and target present (TP).we are only interested in the general tendenciesof the false acceptances (the picking of thewrong voice) and the true, i.e. correct identifications.In Figure 1 we present the false acceptancesgiven by the different age groups and alltogether.In Figure 1 it is very clear that false acceptanceis biased toward certain speakers such asspeaker CF followed by MM and JL. It is noticeablethat correct acceptances in TP was 27and that can explain the decrease in FA for MMand JL, however, the degree of FA for speakerCF is even higher in TP (28).N/second76543210Articulation RateCF JÅ JL KG MS MM NS TN PoCSpeakerFigure 2. Articulation rate (produced syllables persecond) for the speakers in the line-up.In Figure 2 we can see that the target (PoC)was produced with a fast articulation rate. Severalspeakers follow with rather average valuesaround 5 syllables per second. The speakerwith the highest AR compared to PoC is CF. InFigure 3 we take a closer look at pausing.ARPauses tend to increase in duration with higharticulation rate (Goldman-Eisler, 1961).N/min (%)454035302520151050Pausing for Line-up SpeakersCF JÅ JL KG MS MM NS TN PoCSpeakersPausdur/minPaus_N/minPaus_%Figure 3. Pausing (pause duration per minute, numberof pauses per minute and percentage pause fromtotal utterance duration) for the speakers in the lineup.The pausing measurement shows a bias towardsspeaker CF, which might explain some of thefalse acceptances.The perception test resultsBoth listening tests separately (controlled anduncontrolled) show significant inter-rateragreement (Cronbach’s alpha = 0.98 for thecontrolled and 0.959 for the uncontrolled test).When both datasets are pooled the inter-rateragreement remains at the same high level (alpha= 0.975) indicating that listeners in bothsubgroups have judged the voices the sameway. This justifies using the pooled data from188
Proceedings, FONETIK 2009, Dept. of Linguistics, Stockholm Universityboth groups (52 subjects altogether) for the furtheranalysis of the perception test results.Mean similarity4,543,532,521,510,50Mean Voice Similarity Judgement Speakers vs. PoCJÅ JL KG MM MS PoC NS TN CFSpeakerFigure 4. Mean voice similarity judgment by listenerscomparing each speaker against target PoC. Thecloser to 1 the more similar voice according to judgments.The voice similarity judgments indicate thesame as the line-up regarding speaker CF, whois judged to be closest to the target followed byJL and MM. It is also noticeable that thosespeakers are among the speakers who get thehighest mean overall similarity judgmentscompared to all the other speakers.Table 1. The table shows speaker ranks based onmean similarity judgment for both listener groupspooled.Speaker JÅ JL KG MM MS PoC NS TN CFJÅ 1 4 5 3 6 8 9 7 2JL 3 1 8 5 7 4 2 9 6KG 5 9 1 2 3 7 8 6 4MM 4 5 2 1 3 8 9 7 6MS 7 8 6 5 2 9 3 1 4PoC 5 3 6 4 9 1 7 8 2NS 6 2 8 5 3 7 1 9 4TN 6 9 5 4 1 7 8 2 3CF 2 9 6 7 3 5 8 4 1Mean 4.3 5.6 5.2 4.0 4.1 6.2 6.1 5.9 3.6rankStd dev 2.0 3.2 2.4 1.8 2.6 2.5 3.2 2.9 1.7The mean rank in table 1 indicates how thespeaker is ranked compared to the other voicesin similarity judgment.PoCthat CF is generally judged as most similar tothe target speaker (even more than the actualtarget in the TP line-up). We have also foundthat the result can partly be explained by thesimilarity in speaking tempo parameters. However,since the result is also confirmed in theperception experiment it must mean either thatthe tempo parameters are still obvious in backwardspeech or that there is something else thatmake listeners choose certain speakers. Perhapsthe indication that speakers are generally highranked, or wolves (term from speaker verification,see Melin, 2006), in combination withsimilar aspects of tempo make judgments biased.More research to isolate voice quality isneeded to answer these questions in more detail.AcknowledgementsMany thanks to the participants in the listeningtest. My deepest gratitude to the AllEars projectLisa Öhman and Anders Eriksson for providingme with data from the line-up experiments beforethey have been published.ReferencesFrench, P., and Harrison, P. (2007) PositionStatement concerning use of impressionisticlikelihood terms in forensic speaker comparisoncases, with a foreword by PeterFrench & Philip Harrison. InternationalJournal of Speech Language and the Law.[Online] 14:1.Künzel, H. (1997) Some general phonetic andforensic aspects of speaking tempo. ForensicLinguistics 4, 48–83.Goldman-Eisler, F. (1961) The significance ofchanges in the rate of articulation. Lang.and Speech 4, 171-174.Öhman, L., Eriksson, A. and Granhag, P-A.(2009) Unpublished Abstract. Earwitnessidentification accuracy in children vs.adults.Comparison of results and discussionThe purpose of the study was to compare thegeneral results from the line-up study and theresults of the perception experiment presentedhere. A comparison between the results show189
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Proceedings Fonetik 2009 - Institutionen för lingvistik

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