Liar Liar Pants on Fire

The U.S. government has long relied on polygraphs when checking the backgrounds of job applicants at intelligence agencies or of people who have access to classified information. And since the terrorist attacks of September 11, federal agencies have escalated their use of lie detectors. The FBI says it is planning to start hooking agents up to polygraphs more often to root out moles like Robert Hanssen, who sold secrets to Moscow for nearly two decades. The Justice Department has begun to test hundreds of workers at facilities where anthrax is stored, in hopes of discovering who sent the deadly spores through the mail last fall.


But even its most ardent advocates admit that the polygraph is accurate only about 90 percent of the time, and that its error rate rises when used for anything other than investigations in which enough evidence exists to formulate specific questions. The polygraph is unreliable because it doesn't read minds. Rather, it measures fluctuations in the rate and depth of breathing, and in perspiration, blood pressure, and pulse, on the assumption that when people lie, they become agitated. That's a recipe for false positives. An innocent person can easily become uncontrollably nervous merely from being strapped to a polygraph and peppered with questions that could land him in jail or get him fired. Mistakes occur frequently enough that a 1988 federal law forbids most private companies from using lie detectors to screen prospective employees. In only one state, New Mexico, are polygraph results admissible as evidence in court without prior agreement of both sides.


There is so much concern about the efficacy of polygraphs, in fact, that the Department of Energy recently sponsored an 18-month study by the National Academy of Sciences to define circumstances in which the device should be allowed. Besides analyzing the effectiveness of polygraphs, the study (which may be released before this article appears) will also evaluate several new lie detection methods that could complement or eventually even replace the polygraph.


What lie detection researchers are looking for is the so-called Pinocchio response-an unmistakable physical sign of deception. To that end, they are experimenting with high-tech brain imaging machines, electroencephalographs, even infrared cameras to find the telltale physiological evidence of a lie. But these researchers are up against more than scientific obstacles; what they have to contend with is the complexity and variety of lies themselves. It's virtually impossible to recreate a real lie-certainly one whose detection would result in meaningful consequences-in a laboratory.