The production and perception of emotional speech is of growing importance to forensic speech scientists. They are often asked by instructing parties to provide an opinion as to whether recordings representing a violent attack are genuine, and whether speech material reflects real distress. However, they are prohibited from making statements regarding the psychological states of speakers by the International Association of Forensic Phonetics and Acoustics Code of Practice (IAFPA 2004).
This study investigates two principal questions. First, it investigates how distress speech can be manifested acoustically. In so doing it proposes a taxonomy for comparing distress speech across speakers, assists in delimiting the boundaries of the vocal repertoire, and considers the extent to which acoustic measures of distress speech can distinguish between the vocalisations of real victims and actors. Second, it investigates whether listeners can discriminate between genuine and acted distress portrayals, and to what extent familiarity with forensic material increases listeners’ ability.
Recordings from authentic criminal cases involving violent attack are compared with re-enactments by trained actors. Acoustic analyses examine F0, intensity, vowel formant frequencies and articulation rate. The recordings are also used as stimuli in a perceptual listening test, comparing the performance of lay listeners, police call takers and forensic practitioners.
The findings lend support to the view that assessments of distress should be exercised with extreme caution. On the one hand, acoustic parameters can distinguish between non-distress and distress conditions, but cannot discriminate between acted and authentic distress, and so IAFPA’s refrain from such an assessment is justified. On the other, listeners who are familiar with authentic distress data, such as police call takers and forensic practitioners, are better able to differentiate between acted and authentic distress than lay listeners. Thus, if an assessment were to be made, the forensic practitioners may be the best group to do so.
