In the late 1960s, Paul Ekman–then a young psychology professor at the University of California, San Francisco, School of Medicine and just commencing his life’s work–filled a San Francisco Victorian with a library of films showing 40 psychiatric patients’ faces as they were interviewed. Ekman, who is now a leading figure in his profession, wanted to know whether he could isolate facial expressions to help diagnose mental disorders. A woman named Mary, who had attempted suicide three times before, smiled and spoke cheerily on her tape. As it happened, she was angling for a weekend pass–so that she could go home and kill herself.

“Mary was how I first discovered microexpressions,” Ekman told me when I caught up with him on the set of Lie to Me, the Fox television drama inspired by his decades of research into how facial expressions, gestures, and other nonverbal behaviors reveal our emotions and–most pertinently–our deceptions. “Some young psychiatrists I was teaching asked whether I could help identify when a suicidal patient was telling the truth or lying about improving,” he said. “Some of their patients had left the hospital and killed themselves within an hour. Mary, however, had confessed before she left that she’d been lying during a [previous] interview I’d filmed. Looking at the film, I couldn’t see any evidence. So I went through it frame by frame for a week, and these microexpressions showed up–two instances, each a 25th of a second, out of 12 minutes.”

In Mary’s case, her features had fleetingly exhibited despair when the interviewing doctor asked about her plans. Ekman learned that the human subjects he studied betrayed their emotional state through microexpressions, however much they tried to suppress them. He identified 46 facial-muscle movements that, across cultures, signal such basic emotions as fear, distrust, and distress.

“What I didn’t know at the beginning,” Ekman told me, “was you could train people to recognize these microexpressions in real time.” He developed the Facial Action Coding System, or FACS, in the 1970s as an exhaustive taxonomy of all facial expressions, including these telltale muscle behaviors. Since then, trained FACS users have generally demonstrated better than a 75 percent success rate in reading faces. Lie to Me–which stars the estimable Tim Roth as Dr. Cal Lightman, the character based on Ekman–is very average entertainment in the genre of Fox’s great success House, where a maverick expert solves cases that establishment types cannot. In reality, however, a lot of FACS users are establishment types–cops, FBI agents, members of the U.S. Secret Service.

It requires no innate gift to apply Ekman’s research in practice. “You could go online now [www.mettonline.com] and learn the microexpression recognition, which is one part, in an hour,” Ekman says. With practice, most of us could decode these fleeting expressions in real time. “Initially, everybody believes they’ll never do it,” he says. “By the end, they’re asking, ‘Are you slowing these things down?’ We’re not, but your eyes have learned to see them.”

Other studies bear out Ekman’s claims. In research conducted in 2006, neuroscientist Tamara Russell of the University of London’s King’s College showed that an hour of microexpression training enabled people with schizophrenia to identify facial expressions as accurately as healthy people.