Trying to spot a liar? Give them something to do as they fib, a new study finds

Since lying taxes the brain more than telling the truth does, an added task — a sort of cognitive load; numbers to remember or a list to memorise — could make it harder for a smooth talker to lie convincingly, a new study out of Portsmouth suggests.

Liars, on TV, invariably have a tell, a tic or gesture just pronounced enough to be noticed by the watchful viewer. The truth, in the real world, is that catching a person in a lie is far more difficult. The cues are far subtler and supremely wide-ranging. For some it may very well be a faint flicker in the eyes; but for many it can be something as imperceptible as a slight change in breathing patterns.

A still from the series Lie to Me (2009), about a psychologist who uses his skill at reading faces to help the police with criminal investigations.

Observe a subject over time and there are verbal cues that give it away too, psychological studies have found. But these cues also differ from person to person. Was there a way, then, to catch out a liar one had only just met? Aldert Vrij, author of Detecting Lies and Deceit (2008) and professor of psychology at the University of Portsmouth, England, has been conducting research in the field for three decades. This year, the results of his latest experiment were revealed: an attempt to use cognitive load to sift truth from untruth.

The experiment used as its foundation the hypothesis that lying must strain the average brain more than telling the truth. What if one were to strain the brain further, with, for instance, a task to be performed? Would a clearer difference emerge between liars and truth-tellers?

Vrij and his team tested their theory on 164 subjects in the UK (49 male and 115 female). Each subject was asked their opinion on three controversial news developments (Brexit, smoking bans, abortion, etc). The test group was made up of people who had been requested to lie, falsifying their opinions. The control group was truth-tellers asked to report their genuine feelings. And two-thirds of the volunteers across both groups were given an additional mental task: they had to remember a car-registration number and repeat it back to the moderator at the end of the discussion.

The results were revealing. In a study report published in the International Journal of Psychology and Behavior Analysis in May, Vrij and his team reported that the addition of a memory test caused changes in speech patterns among both liars and truth-tellers, but that the changes were intensified for the liars.

When measured on a scale created for the experiment, the liars with the car-registration number to remember suffered a 25% dip in immediacy, clarity and directness, when compared to truth-tellers with the same number to remember.

“The most diagnostic differences between truth-tellers and lie tellers occurred in plausibility, immediacy, directness and clarity,” the study report states. “If you distract interviewees during their story-telling task, lie tellers are more affected than truth tellers making the difference between the two more pronounced.”

Of course, as the study admits, there are plenty of people that can perform complex tasks while twisting the truth and making details up entirely. We see those on TV a lot too. Except they’re always on the news, and you can never really tell with them, can you?