Voice Identification: The effect of Age and Presentation Format

Abstract: Degree of Licentiate in Psychology Abstract Öhman, L. (2010). Voice ldentification: The Effect of Age and Presentation Format. Department of Psychology, University of Gothenburg, Sweden In some criminal cases the victim's or witness's memory of the perpetrator's voice may be an important clue and therefore have a vital role in both the investigative phase and in court. Examples of such situations are crimes committed under conditions of darkness or by disguised perpetrators, such as hooded rape or robbery. Another category is crimes committed over the phone such as obscene phone calls, fraud calls and other threatening phone calls. Although earwitness observations are not as unusual as one may think, witnesses' memory for voices is, compared to eyewitness identification, a much neglected research area. People of all ages can become victims of and/or witnesses to a crime, therefore it is important to assess voice identification performance for different age-groups. In the current thesis children and adults were tested with respect to their ability to identify an unfamiliar voice (Study I). The common use of mobile phones in today' s society is mirrored by the high number of criminal cases where mobile phones are involved. Hence, the present thesis investigates the effect of being exposed to a voice via mobile phone on voice identification accuracy (Study II). Both studies used the same setup, which included the exposure of an unfamiliar voice for 40 seconds, and a seven-voice lineup after a two week delay. The aim of Study I was to explore the earwitness performance of children aged 7-9 (N = 95) and 11-13 (N = 78), and adults (N = 91). Half of the participants were exposed to a target-present lineup (T-P), and the other half to a target-absent lineup (T-A). For both types oflineups the participants performed poorly. In the T-P condition only the 11-l3-year olds (with 27 % correct identifications) performed above chance level (12.5%, 8 possible alternatives). Furthermore, in the T-A condition all age-groups showed a high wiIlingness to make an identification (overall mean = 53%). For both groups of children, voice identification co-varied significantly with speaking rate and pitch level, as did pitch variation for the youngest children. Neither factor correlated significantly with the aduIts' identifications. The aim of Study II was to investigate the influence of presentation format (direct recorded voices vs. mobile phone recorded voices) on voice recognition accuracy. The participating adults (N = 174) were assigned randomly to one of the four conditions (Initial exposure: direct vs. mobile phone recorded voice; Lineup presentation: direct vs. mobile phone recorded voices). The overall accuracy for correct identification was 12.7%, which is expected by chance (12.5%), and more than half of the participants (57%) made a false identification. Further, the resuIts did not reveal any significant effect of presentation format or lineup format. These results suggest that the detrimental effect on voice recognition suggested by the poorer sound quaIity of mobile phone recordings is minimal. They also indicate that there is no benefit from conducting a mobile phone recorded lineup, ifthe voice is originally heard over a mobile phone. In sum, the effect of age and presentation format was found to be very small. However, the overall conclusion that follows from the present thesis is that earwitnesses seem to be poor at making a correct decision when confronted with a voice lineup. Actors in the legal system should therefore treat voice identification evidence with caution. Keywords: earwitness, voice identification, voice lineup, children, presentation format, mobile phone Lisa Öhman, Department ofPsychology, University of Gothenburg, P.O. Box 500, 405 30 Gothenburg, Sweden. Phone:+46317861934, E-mail: [email protected] ISSN l101-718X ISRN GU/PSYKJAVH--238--SE