Shifting uncomfortably in your seat? Stumbling over your words? Can’t hold your questioner’s gaze? Police interviewing strategies place great emphasis on such visual and speech-related cues, although new research funded by the Economic and Social Research Council (ESRC) and undertaken by academics at the University of Portsmouth casts doubt on their effectiveness. However, the discovery that placing additional mental stress on interviewees could help police identify deception has attracted interest from investigators in the UK and abroad.
Police manuals recommend several approaches to help investigators decide whether they are being told the truth. The principal strategy focuses on visual cues such as eye contact and body movement, whilst the Baseline Method strategy sees investigators compare a suspect’s verbal and non-verbal responses during ‘small talk’ at the beginning of interview with those in the interview proper. A third, the Behavioural Analysis Interview (BAI) strategy, comprises a list of questions to which it is suggested liars and those telling the truth will give different verbal and non-verbal responses.
However, research has consistently found that cues offered in each of these scenarios are unreliable – a view confirmed by the ESRC-funded ‘Interviewing to Detect Deception’ study. A series of experiments involving over 250 student ‘interviewees’ and 290 police officers, the study saw interviewees either lie or tell the truth about staged events. Police officers were then asked to tell the liars from the truth tellers using the recommended strategies. Those paying attention to visual cues proved significantly worse at distinguishing liars from those telling the truth than those looking for speech-related cues. In another experiment, liars appeared less nervous and more helpful than those telling the truth – contrary to the advice of the BAI strategy.
Professor Aldert Vrij explained: “Certain visual behaviours are associated with lying, but this doesn’t always work. Nor is comparing a suspect’s responses during small talk, and then in a formal interview, likely to be much help. Whether lying or telling the truth, people are likely to behave quite differently in these two situations.”
He continued: “Evidence also suggests that liars are concerned about not being believed, and so are unlikely to come across as less helpful than truthful people during interview. If anything, guilty people are probably even keener to make a positive impression. All of this makes the investigator’s job very difficult.”
However, the picture changed when researchers raised the ‘cognitive load’ on interviewees by asking them to tell their stories in reverse order. Professor Vrij explained: “Lying takes a lot of mental effort in some situations, and we wanted to test the idea that introducing an extra demand would induce additional cues in liars. Analysis showed significantly more non-verbal cues occurring in the stories told in this way and, tellingly, police officers shown the interviews were better able to discriminate between truthful and false accounts.”
