We all want to know when someone is lying. The problem is that cues to deception are typically faint and unreliable.
One way to try to ascertain whether someone is lying is to actively elicit and amplify verbal and nonverbal cues to deceit. How can we do this? The short answer is by increasing the cognitive load on the possible liar.
Despite its impressive abilities, the human mind has a limited capacity for hor much thinking it can handle at any time. If you can increase the cognitive burden, it is possible to compromise normal information processing. Increasing the cogntitive burden aims to make it harder for liars to lie because this affects liars more then truth-tellers and results in more and, importantly, more blatent detectable behaviorial clues to deception.
Here are two strategies to increase the cognitive burden on the potential liar:
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.