Mind & Body

To Catch Someone in a Lie, Science Says Go Low-Tech

Since humans could talk, humans have also probably dreamed of an easy way to tell if others are lying — something obvious, like how Pinocchio's nose gets longer when he tells a fib. Nowadays you'd think technology could solve this problem, but so far, not so much. In fact, recent research suggests we are never going to be able to depend on any simple trick to detect deception. What does work is being smart and strategic about how you ask questions and listen to the answers.

Does Your Body Reveal That You're Lying?

Everyone's familiar with the lie detector machine, and not just as a prop in TV cop shows. This machine, known as a polygraph, is used by real-life law enforcement and intelligence agencies, including the FBI and the CIA. They use it not only for identifying criminals but also for employment screening. The polygraph measures physical signs, including heart rate, blood pressure, sweat, and breathing rate, with the idea that people who are lying are anxious about it and these physiological measures will give that away.

With such high-profile organizations putting their trust into the polygraph, it must be reliable, right? Not really. It's been known for quite a long time that it doesn't work. The problem is that while those measures will indeed show whether someone is anxious, anxiety isn't perfectly correlated with lying. Many truthful people are anxious during a high-pressure interrogation, so the test produces a lot of false positives. And people who are good at lying might not be anxious about it at all, so the test won't pick them out.

A more recent approach that claims to pick up on the physical cues that someone is lying is the Micro-Expressions Training Tool, or METT. Rather than a machine, the METT is a training strategy that teaches human beings to detect liars by looking for tiny, fleeting "micro-expressions" that people supposedly make when they aren't being truthful.

This approach is already used in many settings, including airport security, which is bad news considering that a recent study showed that it may, in fact, be worse than useless. In the study, 90 subjects were given either METT training, bogus "placebo" training, or none at all, and asked to watch videos of people either lying or telling the truth. The participants simply had to tell the difference between the truth and a lie. In the end, those who had been trained on METT were slightly worse at identifying liars than randomly guessing. Yikes.

Listening to Liars

Should we give up hope for a systematic way to keep bad guys from fooling us? Recent research shows that not all is lost, but the most effective methods are going to take more effort than just measuring Pinnochio's nose. In fact, the "trick" is — wait for it — listening to what people are saying.

To be fair, it's a little more than that; how you ask the questions is also crucial. Much of this research is based on the idea that telling a lie is simply harder mental work than telling the truth. Ask any writer: Making up a story takes more effort than simply transcribing something that happened. And like a writer, a liar has to make sure to keep all the fictional details in their memory and sound convincing when explaining them.

That means that if you add more cognitive challenges to that task, liars will struggle when the truthful don't. One trick that seems to work is asking the person to tell their story in reverse order. This is harder when the story isn't true and makes it easier for observers to tell that the subject is lying.

An even more basic approach that helps is to just ask more questions, especially unexpected ones. Truth-tellers can easily find more to say, but it's a challenge for a liar to come up with something that's not in his prepared story on the spot.

Some other science-backed techniques actually do match what fictional law enforcement might do. For example, research suggests that the investigator shouldn't lay all their cards on the table at the start, but only gradually reveal what evidence they have against the suspect. The liar's stories may then be inconsistent with that evidence, making it clear they're lying.

So it looks like there are ways to boost the chances of catching a lie; we've just been basing our approaches on the wrong stories. Systematic ways of tripping people up in conversation seem to work better than any hand-wavy pseudoscience about eye movement or science-fictiony lie-detector machines. To spot a liar, watch less and listen more.

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Everyone lies now and then, but in the book "Lying," best-selling author and neuroscientist Sam Harris argues that you can simplify your life by always telling the truth — even in those everyday situations where a lie makes sense. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Linda Lombardi October 11, 2019

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