In the ‘90s, psychologist Paul Ekman leapt to fame with his theory of "microexpressions"-the idea that when we lie brief, subconscious flashes of emotion register on our face to reveal our true feelings. People trained to pick up on these cues, Ekman said, can root out the truth with astonishing accuracy. His idea inspired a $1 billion TSA program and the TV show Lie to Me.

There's just one problem. There's no evidence that Ekman's theory has any basis. "It's hokum," says Yale psychologist Charles Morgan III. While something like the microexpressions that Ekman described do exist, truth-tellers exhibit them as well as liars. "There is no clue, no behavior, that always means that someone is lying, and never means something else," says Bella DePaulo, a psychologist at the University of California, Santa Barbara who studies lying (and fellow PT blogger). "All of these behaviors are just hints."

So can science help us unmask deception? Yes. But the key is not just to observe a suspected liar but to ask them the right kind of questions. Making up a story and keeping the details straight require more mental horsepower than just telling the truth. Researchers have found that if interrogators can place an extra "cognitive load" on a liar's intellect they'll likely push it to breaking point and cause the story to fall apart.

Dutch psychologist Aldert Vrij has tested several ways to accomplish this. In one experiment, he asked pairs of subjects to either go eat lunch together in a restaurant or to simply lie and say that they had. Vrij found that when it came to the kinds of questions that they probably expected to face -- "what did you do in the restaurant?" -- the liars were able to come up with such convincing stories that it was impossible to tell the two groups apart. But when he forced them to respond on the fly to unexpected questions, such as queries about spatial layout ("In relation to where you sat, where were the closest diners?''), the liars gave up the game 80 percent of the time.

So if you want to get the truth, sit your suspected liar down for a chat and lay some cognitive load on them. Here are four proven techniques based on experiments that Vrij and others have conducted.

  1. Ask them to tell the story in reverse. Having to relate a sequence of events in backward order is mentally taxing, and even more so when the storyteller can't just pull the pieces from memory. The extra effort should overload a liar's cognitive wherewithal.
  2. Tell them to look you in the eye as they tell the story. It's a myth that liars can't look you in the eye-some may even do so more than usual. But having to continuously direct their gaze into your eyes is a cognitively demanding task that could distract a liar's focus away from the story that he's trying to keep straight.
  3. Ask them to draw the scene. When someone is lying they generally make up a story with as little detail as possible. If you ask them to draw a picture of the scenario in question, they'll be forced to come up with additional visual details. Their pictures will be less detailed than a truth-teller's and may contradict what they've already told you.
  4. Don't show what you know. A up-and-coming new technique for police interrogators is called "strategic use of evidence," or SUE. It involves sprinkling pieces of information that you already know about the disputed circumstance into your line of questioning. By leaving the suspect guessing about how much you know, you'll force him to lie defensively-and hopefully, to give up facts you didn't already have.

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