Brain scans detect lies more accurately than the polygraph
It’s a common scene from an episode of a TV crime drama: A suspect is strapped to a polygraph machine. He sweats. He squirms. His eyes dart from one direction to the other. The needle on the polygraph machine swings wildly, indicating that the suspect is lying.
In fact, increases in one’s blood pressure or pulse, or the presence of sweaty palms, are no longer seen as telltale signs of lying: Since the 1980s, polygraphs have been deemed inadmissible as legal evidence in a majority of jurisdictions in the U.S. and for most pre-employment screenings.
However, polygraphs remain the only biological method of lie detection in use in the U.S. in certain instances, such as government background checks and security clearances.
In recent years, researchers have successfully used functional magnetic resonance imagining, or fMRI, to map brain activation patterns associated with intentional deception. Neuroimaging studies have also shown that fMRI is fairly accurate in detecting deception in individuals. However, experts agree that use of fMRI in real-life police or forensic work remains impractical without extensive testing and validation.
Daniel Langleben, a professor of psychiatry; his colleagues at the Perelman School of Medicine; and Ronald Barndollar, a FBI supervisory agent and polygraph examiner, set out to fill in one of those gaps by comparing the polygraph and fMRI in lie detection. The study, published in the Journal of Clinical Psychiatry, found that experts reading fMRI data were 24 percent more likely to detect a lie from a study participant than professional examiners reviewing polygraph recordings.
The study was the first to compare polygraph testing and fMRI under nearly identical conditions and in the same participants—which was no small task, says Langleben, since the tests are administered and evaluated differently.
He explains that with a polygraph, an examiner asks questions of the subject until there is enough data to make a determination. The recordings are usually read by the same person who administers the test. Although automated software packages for scoring polygraph data are included with most digital systems, examiners rarely rely on them to make determinations.
Comparatively, fMRI tasks are programmed in advance and do not change between participants; the scanner operator interacts with the testee via intercom and only in an emergency. Experts do not compare results. It is, as Langleben says, “an almost ideal experimental environment.”
The challenge, he says, was in setting up an experiment where two dissimilar technologies are used under conditions similar enough to allow a head-to-head comparison.
“We decided that since it’s new technology that needs to prove itself against the old—or to be polite, ‘state of the art’ technology—the old technology should be the starting point. In our case, this meant that MRI examiners were asked to act as if they were polygraph examiners,” Langleben says. “The point of the study was not to achieve the best performance either technology is capable of [but] to compare their performance under identical techniques.”
The researchers gave 28 participants the “Concealed Information Test,” which is designed to see if people have specific knowledge that in a real-life situation could be incriminating, through a series of questions, some of which have known answers. A researcher asked participants to write down a number between three and eight, keep it hidden, and not admit to having written a number. Next, participants were hooked up to a polygraph or were scanned by a fMRI machine and asked whether they had written a certain number. People were instructed to answer “no” to all questions, making one of their answers a lie. At the end of the session, participants handed their hidden notes to the designated team member who placed them in a sealed envelope in a locked box. The results were analyzed by three polygraph and three neuroimaging experts independently of one another and then compared to see which technology was more accurate in detecting the lie of each participant.
Overall, fMRI experts were 24 percent more likely to detect the lie. Langleben and his colleagues discovered another important point, too: When everyone agreed on the number that the participant was lying about, fMRI and polygraph experts turned out to be 100 percent correct. This happened in 17 cases and suggests the two tests may complement each other.
Langleben says the study was not designed to prove this unexpected observation, but it points to a potentially useful approach in countries that adhere to the “guilty until proven otherwise” principle. If the suspect can pass sequential MRI and polygraph tests, “the chances he/she is lying are very low,” he says. “This could be brought up as evidence of ‘reasonable doubt’ leading to acquittal or reduced punishment.”
Langleben says people should be open to the possibility and power of a brain scan.
“Imaging is the most powerful technology that we have so far for looking at how the living brain works,” he says. “This work is important not only as a lie detection project, but especially because it opens doors and windows to all kinds of related fundamental phenomena, such as delusions, self-deception, and insight.”
