To Catch a Liar

For some reason I'm not sure about, this post, which originally appeared on Poe's Deadly Daughters in September 2011, has been used in two textbooks published by Pearson, and now I've received a request for its use in a third. Since few people read it the first time around, I thought it might find some new readers here.
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Do you think you’re pretty good at spotting a liar?

Sorry, but I’ll bet you’re not as sharp as you think you are.

Researchers have found that most people have a dismally low success rate, even in a lab setting where they know for certain that some of those they’re studying are lying. If we’re especially vigilant, we might spot half of all lies – which means we’ll miss half. Police officers aren’t much better than the rest of us, although they improve with experience. Those super-cops who can always detect a lie, like the fictional Special Agent Gibbs on the TV show NCIS, do exist in reality, but they’re extremely rare and psychologists have yet to determine how they do it.

Since the detective’s ability to spot lies is crucial to crime-solving, some scientists are finding ways to teach the skill to cops. Scientific American Mind magazine’s September/October issue reports on experiments conducted by one of them, social psychologist Aldert Vrij of the University of Portsmouth in England. Vrij’s work is based on the human mind’s inability to think along multiple tracks simultaneously. Lying is more demanding than simply telling the truth, so if the interrogator gives the suspect’s mind too much to process at one time, the person being questioned is likely to slip up if he’s trying to sell a phony story.

Here’s the premise: The liar has to worry about keeping his story consistent and believable, first of all – which means suppressing all thought of the truth so it doesn’t inadvertently slip out – but he also has to “look honest” by controlling his expression and body movements.  And he’s constantly monitoring the cop’s reaction to what he’s saying. All that is exhausting, and if the interrogator adds even a little more pressure, that may be enough to trip up a liar.

Vrij and his colleagues have found several useful strategies for applying that extra pressure.

First, discount sweating and general nervousness. Even an honest person will be nervous under police scrutiny.

One way to trip up a liar is to ask the suspect to tell his or her story backward, beginning at the end. Devising a false story and keeping it straight is hard enough without the burden of having to recount phony events in reverse. In lab tests, this greatly increased mistakes and the likelihood of catching a liar.

Interrogators can also rattle a suspect by insisting that he maintain eye contact. Liars have trouble concentrating on their stories if they’re looking directly into the eyes of the people they’re lying to.

Asking suspects to draw pictures of what they’re describing can also reveal the liars. Their pictures will show fewer details than those drawn by truth-tellers, and often the pictures won’t be consistent with verbal descriptions.

These easy techniques have proven highly effective in the lab and should help police in the real world do their work more efficiently. Best of all, they’re simple enough to be used by fictional cops who aren’t endowed with the special mental powers of Special Agent Gibbs.