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Technology

Liar, Liar, Face on Fire

The real truth is written all over your face.

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Polygraph lie detectors are notoriously unreliable: 10 percent of liars pass, and 20 percent of truth tellers fail. But the real truth is written all over your face, says cognitive scientist Marian Stewart Bartlett, at the Institute for Neural Computation in San Diego. Every emotion a person feels elicits an involuntary facial expression, but often just for a split second. When someone tries to cover those emotions, the expression passes so quickly most people miss it.

Now there's a way to catch liars in the act. Bartlett and several colleagues at the Salk Institute have developed a high-speed computer program that analyzes videotapes to automatically detect a subject's microexpressions. The program superimposes a grid over a baseline black-and-white photograph of the subject's face devoid of all expression. Any change in expression, no matter how subtle or fast, registers on the grid as a departure from baseline. For example, if eyebrows lower in anger, they leave their neutral position--a movement documented by the computer. "The method it uses," Bartlett says, "is based on the way the brain interprets vision." The neurons that deal with vision each look at a different part of an image, and the brain assembles the information.

Microexpression analysis provides other information conventional polygraphs can't. For example, a man accused of killing his wife could become angry and fail the polygraph--guilty or innocent. But with the same response in Bartlett's test, "We could see if his reaction was anger (at being unjustly accused). But disgust (at himself for his actions) would suggest that he might be guilty."

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