What tricks can you use to determine if someone is telling the truth?
In this report, Aldert Vrij of the University of Portsmouth, Anders Granhag of the University of Gothenburg, and Stephen Porter of the University of British Columbia review research suggesting that verbal methods of deception detection are more useful than nonverbal methods commonly believed to be effective, and that there are psychological differences between liars and truth-tellers that can be exploited in the search for the truth.
In an information-gathering interview suspects are asked to give detailed statements about their activities through open questions—for example, “What did you do yesterday between 3 p.m. and 4 p.m.?” This interview style encourages suspects to talk and allows for opportunities to identify inconsistencies between the answer and available evidence. Asking very specific questions that a suspect is unlikely to anticipate may also help in lie detection.
Lying can be more cognitively demanding than truth-telling—it requires more brain power to come up with a lie and keep track of it (e.g., who was told what) than it does to tell the truth. Imposing cognitive load on interviewees by asking them to recall the events in reverse order may also be useful in weeding out liars from those telling the truth.
One intriguing strategy is to demand that suspects tell their stories in reverse. Narrating backward increases cognitive load because it runs counter to the natural forward sequencing of events. It also disrupts the normal reconstruction of past events using mental schemas, which give coherence to isolated events. Since liars already have depleted cognitive resources, they should find this unfamiliar mental exercise more taxing than truth tellers do—which should increase the likelihood that they will somehow betray themselves. And in fact that’s just what happens in the lab: Vrij ran an experiment in which half the liars and truth tellers were instructed to recall their stories in reverse order. When observers later looked at videotapes of the complete interviews, they detected more clues to deceit in the liars who were burdened by this mental task. Indeed, observers correctly spotted only 42 percent of the lies in the control condition—way below average, which means they were hard to spot—but a remarkable 60 percent when the liars were compromised by the reverse story telling.
Another strategy for increasing liars’ cognitive burden is to insist that suspects maintain eye contact. When people have to concentrate on telling their story accurately—which liars must, more than truth tellers—they typically look away to some motionless point, rather than directly at the conversation partner. That’s because keeping eye contact is distracting, and makes narration more difficult. Vrij also tested this strategy in the lab, and again observers detected more clues to deceit in those who were required to look the interrogator in the eyes.