Effects of Suspect Demeanour on Eyewitness Judgments

Eyewitness evidence plays a crucial role in forensic investigations. It can also be unreliable, with eyewitness reports and identifications vulnerable to distortion by various biasing influences. We investigated how eyewitness identification decisions are biased by subtle behavioural or demeanour cues. Specifically, a smiling face has been shown to enhance feelings of familiarity; consequently, the presence of this cue could make a lineup member appear more familiar than other non-smiling members. Witnesses viewed two mock-crimes for either a short or long exposure duration and attempted an identification of the culprits from culprit-absent photolineups. In one condition, all lineup members had neutral facial expressions; in the other, one had a smiling face. For witnesses with a weak memory of the culprit (due to a brief exposure at the time of the crime), the smiling (innocent) lineup member was more likely than other lineup members to be the one rated as being most like the culprit. The biasing effects of such demeanour cues increase the risk of mistaken eyewitness identifications. The broader implications of these findings for how judgment and decision-making in other forensic contexts (e.g., clinical forensic interviewing, evaluating the veracity of testimony) may be biased by demeanour cues will be discussed.