How to Spot a Liar

Few things are easier than telling a lie, and few things are harder than spotting one when it's told to us. We've been trying to suss out liars ever since Cain fibbed to God about murdering Abel. While God was not fooled--hearing the blood of Abel crying out from the land--the rest of us do not have such divine lie-detection gifts.

But that doesn't mean we're not trying. In the post-9/11 world, where anyone with a boarding pass and a piece of carry-on is a potential menace, the need is greater than ever for law enforcement's most elusive dream: a simple technique that can expose a liar as dependably as a blood test can identify DNA or a Breathalyzer can nail a drunk. Quietly over the past five years, Department of Defense agencies and the Department of Homeland Security have dramatically stepped up the hunt. Though the exact figures are concealed in the classified "black budget," tens of millions to hundreds of millions of dollars are believed to have been poured into lie-detection techniques as diverse as infrared imagers to study the eyes, scanners to peer into the brain, sensors to spot liars from a distance, and analysts trained to scrutinize the unconscious facial flutters that often accompany a falsehood.

At last they may be getting somewhere. Next month No Lie MRI of San Diego, a beneficiary of some of that federal largesse, will roll out a brain-scan lie-detection service it is marketing to government and industry. Another company, Cephos of Pepperell, Mass., hopes to follow within a few years.

Even as those outfits ramp up, however, civil libertarians are sounding warnings. It's one thing for airport screeners to peek inside your shoes or squeeze your toothpaste tube. It's another when they pull you aside for questioning because you set off alarms on some scanning device whose reliability could be shaky. And who knows what techniques are already in use at Guantánamo and other extralegal holding pens?

"First, we need to determine how good this science is," says Stanford University law professor Hank Greely. "Then we must decide what it can be used for."

For a technology that so many people dream of improving, lie detection has been advancing at a glacial pace. It was 85 years ago that the venerable polygraph was introduced, and while its results are still not admissible in most criminal courts, it is at least based on a sound premise. Most of us lie easily, but we don't lie well, particularly when the truth could land us in hot water. Fibbing causes the heart to pound, breathing to accelerate and sweating to increase, and the polygraph measures all those things. Sometimes the machine works fine, but often the experience of being wired up to a piece of gadgetry and asked questions by an unfriendly stranger can produce the same symptoms as a lie. Moreover, the best liars tend to be the least troubled by their dissembling and produce the fewest outward clues. Polygraph advocates like to say the technology is 85% to 90% accurate in criminal investigations, but just three years ago the National Research Council of the National Academy of Sciences dismissed the machines as useless. Says University at Buffalo social psychologist Mark Frank: "Even the greatest technology used at gunpoint is worthless."