At Airports, a Misplaced Faith in Body Language

Like the rest of us, airport security screeners like to think they can read body language. The Transportation Security Administration has spent some $1 billion training thousands of “behavior detection officers” to look for facial expressions and other nonverbal clues that would identify terrorists.

But critics say there’s no evidence that these efforts have stopped a single terrorist or accomplished much beyond inconveniencing tens of thousands of passengers a year. The T.S.A. seems to have fallen for a classic form of self-deception: the belief that you can read liars’ minds by watching their bodies.

Most people think liars give themselves away by averting their eyes or making nervous gestures, and many law-enforcement officers have been trained to look for specific tics, like gazing upward in a certain manner. But in scientific experiments, people do a lousy job of spotting liars. Law-enforcement officers and other presumed experts are not consistently better at it than ordinary people even though they’re more confident in their abilities.

“There’s an illusion of insight that comes from looking at a person’s body,” says Nicholas Epley, a professor of behavioral science at the University of Chicago. “Body language speaks to us, but only in whispers.”

The T.S.A. program was reviewed last year by the federal government’s Government Accountability Office, which recommended cutting funds for it because there was no proof of its effectiveness. That recommendation was based on the meager results of the program as well as a survey of the scientific literature by the psychologists Charles F. Bond Jr. and Bella M. DePaulo, who analyzed more than 200 studies.

In those studies, people correctly identified liars only 47 percent of the time, less than chance. Their accuracy rate was higher, 61 percent, when it came to spotting truth tellers, but that still left their overall average, 54 percent, only slightly better than chance. Their accuracy was even lower in experiments when they couldn’t hear what was being said, and had to make a judgment based solely on watching the person’s body language.

“The common-sense notion that liars betray themselves through body language appears to be little more than a cultural fiction,” says Maria Hartwig, a psychologist at John Jay College of Criminal Justice in New York City. Researchers have found that the best clues to deceit are verbal — liars tend to be less forthcoming and tell less compelling stories — but even these differences are usually too subtle to be discerned reliably.

One technique that has been taught to law-enforcement officers is to watch the upward eye movements of people as they talk. This is based on a theory from believers in “neuro-linguistic programming” that people tend to glance upward to their right when lying, and upward to the left when telling the truth.

But this theory didn’t hold up when it was tested by a team of British and North American psychologists. They found no pattern in the upward eye movements of liars and truth tellers, whether they were observed in the laboratory or during real-life news conferences. The researchers also found that people who were trained to look for these eye movements did not do any better than a control group at detecting liars.

“There is no Pinocchio’s nose — no one cue that will always accompany deception,” says an author of the eye-movement study, Leanne ten Brinke, a psychologist at the University of California, Berkeley.

She and some researchers argue that it may nonetheless be possible to detect certain kinds of “high stakes” lies by training experts to look for a constellation of body cues. Stephen Porter of the University of British Columbia says the poor success rate in studies is caused partly by the limitations of laboratory experiments in which subjects are often asked to lie about things that don’t really matter to them. Liars may show more stress in a real-life situation when much depends on being believed.

In a study last year, psychologists at the University of British Columbia trained professionals in forensics to look for an array of facial expressions and other signs of stress or inconsistency in someone telling a story. Then these professionals looked at news footage of people pleading for the return of a missing relative. Some of the pleaders were sincere, but others were lying (as eventually revealed by evidence that they had already murdered the relative). The trained professionals were able to identify the liars with an 80 percent accuracy rate.

That’s an impressive record, but it’s only one experiment, and many researchers question how reliably these techniques can be applied in the real world. Other studies, including ones involving police interrogations, have found that people are not always better at detecting high-stakes lies than lesser ones. The fear of being charged with a crime can make an innocent person look suspiciously nervous, too.

The T.S.A.’s administrator, John S. Pistole, defended its behavior-detection program last year by saying it identified “high-risk passengers at a significantly higher rate than random screening.” The accountability office report challenged the methodology behind that assertion and questioned the cost-effectiveness of the program. It noted that fewer than 1 percent of the more than 30,000 passengers a year who are identified as suspicious end up being arrested, and that the offenses (like carrying drugs or undeclared currency) have not been linked to terrorist plots.

In experiments at the University of Chicago, Dr. Epley and his colleagues have found that people vastly overestimate how much mind reading they can do by looking at someone’s facial expressions.

“Reading people’s expressions can give you a little information, but you get so much more just by talking to them,” he says. “The mind comes through the mouth.”

Why do we intuitively believe we can read body language? After writing a book on the topic — “Mindwise: How We Understand What Others Think, Believe, Feel, and Want” — Dr. Epley has an explanation.

“When you’re lying or cheating, you know it and feel guilty, and it feels to you as if your emotions must be leaking out through your body language,” he says. “You have an illusion that your emotions are more transparent than they actually are, and so you assume others are more transparent than they actually are, too.”

Even after completing his book, Dr. Epley fell victim to the same illusion this year when he gave his wife a present for her 40th birthday, a plane ticket to go by herself to New York to spend the birthday with her twin brother. When she opened it, she burst into tears, and Dr. Epley assumed she was upset at spending the birthday away from her husband and children.

“I was horrified,” Dr. Epley recalls. “I immediately started wondering if the plane ticket was refundable. After she regained her composure, she said, still in tears, that it was exactly what she was hoping to do but didn’t want to say for fear we’d feel bad. They were tears of joy, but I couldn’t tell that until she told me so.”