Liar Liar Pants on Fire

Later, when questioned about the incident while hooked up to the EEG, the volunteers were instructed to claim they weren't involved.


The results of Vendemia's studies, so far involving about 260 volunteers, suggest that there are predictable patterns of brain activity when people lie. A series of characteristic fluctuations in electrical energy, known as event-related potentials, seem to occur less than half a second after someone tells a lie, according to Vendemia.


Scientists have recognized the connection between lying and brain waves since the early 1990s. Until then, it was known that when a person encounters something unusual-an English word buried in a list of Russian expressions, for example-the brain produces a distinctive wave that's called a P300 because it occurs about 300 milliseconds after the stimulus. But in 1991, psychologist Emanuel Donchin and Lawrence Farwell, his graduate student at the University of Illinois at Urbana-Champaign, took this "oddball paradigm" a step further. Using a mock-crime scenario, they showed that a "guilty" person produces a P300 when presented with a telltale detail of the incident within a group of unrelated words or images.


Based on this research, last year Farwell debuted a commercial lie detection method he calls Brain Fingerprinting. On the strength of it, he was named to Time magazine's list of Top 100 Next Wave Innovators. Farwell claims his machine can prove whether a suspect was at a crime scene based on whether he or she generates P300 waves when shown images of key details from the crime. For example, suppose a murder victim was wearing a green sweater; the killer should produce a P300 response when he sees a picture of the sweater among other articles of clothing, having been told that one of them was worn by the victim.


But like the polygraph, Brain Fingerprinting has its share of detractors, including Farwell's former collaborator Donchin. For instance, Donchin says, a person could produce a P300 spike when seeing the green sweater not because he murdered the man wearing it but because he saw a similar one at a store recently on sale for a surprisingly low price. Consequently, there's no way to ensure that the images shown to a suspect will elicit a response only from a guilty person. Moreover, because Brain Fingerprinting is useful only when specific evidence exists, the U.S. General Accounting Office concluded last October that it is of limited use for the more general screening done by the Pentagon, CIA, FBI, and Secret Service.