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Is there an easier way to detect lies than what you see on TV?

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ResearchBlogging.orgThe TV show Lie To Me focuses on the exploits of an expert in lie-detection as he solves perplexing crimes in his high-tech Washington laboratory. It’s actually fun to watch, especially since it appears to make some effort to get the science right (a real-life expert on lie-detection, Paul Ekman, serves as a science adviser on the show).

One of the show’s premises is that only highly-trained experts (most importantly, its protagonist, Cal Lightman) are capable of sniffing out a well-schooled liar. This too is based in fact. Most of us are very bad at spotting liars, taking their seemingly earnest facial expressions as the real thing. Ekman’s research, along with many others, has shown that it’s possible to detect subtle differences between inauthentic emotional expressions and the real thing. Since telling a lie invokes its own distinctive emotions, it’s possible to see remnants of these emotions by carefully watching a liar in the act of deceit, even when the liar masks his or her true feelings with a feigned emotion.

But what if there was a shortcut in sniffing out a lie, relying on our own instinctual behavior? Would it be possible to improve the lie-detecting abilities of ordinary people without all that training? A team led by Mariëlle Stel had a hunch that our tendency to mimic the physical and facial expressions of the people we are speaking to might help us to tell when they are lying.

They recruited 92 volunteers to participate in a very short conversation. The volunteers were paired up randomly, and one person from each pair was randomly assigned to be the truth-teller or liar. This person was asked before meeting the other participant if he or she would like to make a donation to Amnesty International, and then, randomly, told to either tell the truth or lie about it, with a one-euro reward if they could convince the partner they were telling the truth.

The partners were divided into three groups. The first group was told to mimic the liar/truth-teller’s facial expressions and body movements. The second group was told NOT to mimic. And a final group was given no instructions about mimicry.

Finally, the partners met, sat down, and talked about why the truth-teller/liar chose to donate (or not donate, depending on what they actually did and the instructions about whether or not to lie). After the conversation, the partner became the lie-detector, and was asked to rate on a scale of 1 to 7 whether they believed the other participant was telling the truth about donating to charity. This brief conversation was recorded on video, and trained coders watched each conversant separately, coding their facial expressions and movements. These were then compared, and if the truth-teller/liar’s movements or expressions were repeated by the lie detector within 10 seconds, it was counted as a match. Did the instructions make a difference? Here are the results:


As you might expect, those instructed to mimic did so significantly more than the other two groups. In fact, the amount of mimicking done by each group was significantly different, reflecting the fact that we do naturally mimic the movements of conversational partners.

So did the mimicking have an effect on ability to detect lies? Here are those results:


As you can see, both when the lie detectors were given instructions to mimic and when they were given no instructions, they rated lying as significantly more truthful than telling the truth (on a scale where 1 = “totally not truthful” and 7 = “totally truthful”). Only when lie detectors were explicitly told not to mimic did their truthfulness ratings actually correspond to the behavior of their partners: they rated lying as significantly less truthful than truth-telling.

So while the dozens of tricks employed in Lie To Me can help true experts detect lies, this simple study seems to show that simply telling interviewers not to mimic the behavior of the people they are talking to can make them much better at detecting lies. Unfortunately, that probably wouldn’t make for as exciting a TV show!

Stel M, van Dijk E, & Olivier E (2009). You want to know the truth? Then don’t mimic! Psychological science : a journal of the American Psychological Society / APS, 20 (6), 693-9 PMID: 19422628

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