Speech Science Forum - Kirsty McDougall (University of Cambridge)

Abstract:

Earwitness identification evidence may be called on if a perpetrator’s voice has been heard at the scene of a crime, but not recorded. If a suspect has been located, a voice parade containing a sample of the suspect’s voice alongside a selection of foil voices may be constructed and the witness asked if they are able to recognise the perpetrator’s voice in the parade. Earwitness identification of this sort can constitute crucial evidence, yet there remain many unanswered questions about the phonetic and psychological underpinnings of this type of identification and about the optimal way to collect such evidence. In England and Wales, the current procedure for carrying out a voice parade is outlined in a Home Office circular published in 2003. This procedure was developed as an extension of the police procedure for visual identification parades, as informed by the research on earwitness behaviour available at the time. However, developments in psychological research show that while there are some similarities between the processing of faces and voices, considerable differences exist, and further research is needed to determine the best settings of the relevant variables in voice parades (e.g. length of voice samples, number of foil voices, witness instructions, parade type) to minimise earwitness errors. This talk will consider recent findings from the IVIP (‘Improving Voice Identification Procedures’) Project which is investigating ways the Home Office procedure might be adapted to optimise earwitness performance. The talk will also consider issues relating to the assessment of listeners’ perception of voice similarity and the selection of foil voices for a voice parade.