THE general public and the police alike are notoriously poor at spotting when people are lying. But now psychologists have shown that asking suspects to tell their story backwards could significantly aid lie detection. Professor Aldert Vrij and colleagues say the technique works because lying requires more mental effort than telling the truth, so liars are more affected than truth-tellers by the extra cognitive demand of telling their story backwards.
In an initial experiment, 80 undergraduate students were interviewed by a police officer about the theft of a wallet. Half the students had earlier seen the wallet being taken while they played a game of Connect Four, and they were to tell the truth about this in the interview. The remaining students, following a scenario set up by the researchers, had in fact taken a wallet earlier on in the day. They were to lie in the police interview, claiming that they, like the other students, had been playing Connect Four. Half the liars and truth-tellers were required to tell their story forwards, the others told their story backwards.
The demands of telling their story backwards exposed significantly more differences between the liars and truth-tellers than did the task of telling their story forwards. In the reverse story condition, the liars gave fewer auditory details, gave less contextual embedding, made more speech hesitations, and spoke more slowly, all of which are signs of increased cognitive load. They also moved their feet more and blinked more, which are signs of nervousness. By contrast, among the students who told their stories forwards, the liars differed from the truth-tellers only in the fact that they moved their hands and fingers less, probably because of a deliberate effort to appear calm.
In a second experiment, 55 police officers watched video clips of the students being interviewed. Of the students who told their stories forward, the police correctly identified 42 per cent of the liars, which is no better than if they had just guessed. By contrast, of the students required to tell their stories backwards, the police spotted 60 per cent of the liars - better than would be expected by guessing.
Writing in a paper to be published in the journal Law and Human Behaviour, the researchers commented: ‘We believe that the present findings are useful for professional lie detectors and can be adapted for police interviewers.’ Indeed, Professor Vrij told The Psychologist that he has been in contact with several police officers who are willing to try out the technique, and to date feedback from them has been positive. But if this approach became widespread, would it be undermined by criminals practising telling their stories backwards? Vrij acknowledged this is something that remains to be investigated. There also other ways of increasing cognitive load - for example by requiring suspects to maintain eye contact - that the researchers plan to test. CJ