Methods for detecting lies have been around for as long as people have been telling them. There is something comforting in the notion that even the most skilled liar will unconsciously betray himself by some subtle cue--a reddening of the ears, a fidgeting of the hands, an uncontrollable shift of the eyes. But attempts to turn the art of lie detection into a science have always been controversial.

Although an automated version of psychologist Paul Ekman's system for analyzing facial microexpressions to detect deceit may soon be deployed in counterterrorism settings (see "Telling"), and at least two companies are now marketing what they claim is a superior lie detection test based on functional magnetic resonance imaging (fMRI), the polygraph remains the best-known and most widely used lie detector nearly a hundred years after its invention. The polygraph is based on the principle that lying causes a physiological response in the teller that can be reliably measured by a machine and interpreted by a trained technician. In January 1981, a TR report on their then-prevalent use by employers described a typical examination: