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Detecting Lies

From chewing rice to scanning brains, the perfect lie detector remains elusive

An early form of lie detection existed in India 2,000 years ago. Back then, a potential liar was told to place a grain of rice in his mouth, and chew. If he could spit out the rice, he was telling the truth. If he could not, that meant fear of being caught had parched his throat, and his deceit was confirmed.

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Since that time, scientists have searched for a truth tool more reliable than Uncle Ben's—one that can separate fibs from facts with the push of a button. Such a device could slash trial length, aid job screeners and protect borders. The person to fashion this magical instrument—as precise as DNA, and far more applicable—would shift the entire landscape of forensic discovery. It could create a gap in the dictionary between "periwinkle" and "perk," where "perjury" once stood, and a crater in the TV Guide, where "CSI" and all its spin-offs once reigned supreme.

But each advance in the field of lie detection has met with a hitch. Polygraph machines have drawn considerable scientific scrutiny and remain inadmissible in courtrooms. Functional imaging has pinpointed which areas of the brain become active when people lie, but the results are based on group averages and become less accurate when a single person is tested. Even people with incredibly accurate facial analysis skills, so-called lie detection "wizards," were called into question last month in the journal Law and Human Behavior.

What follows is an overview of the long and continued struggle to find the perfect lie detector.

The Polygraph

In the early 20th century, Harvard psychologist William Mouton Marston created his "systolic blood pressure test," more commonly known as the polygraph machine. Marston's hodgepodge of gizmos included a rubber tube and a sphygmomanometer—that childhood favorite the pediatrician wraps around a bicep and inflates with each squeeze of an egg-shaped ball. Polygraph 101 is clear enough: a person has typical levels of heart-rate, respiration and blood pressure when answering a basic question like "Is it true you live at 520 Elm Street?" If these levels remain the same during questions such as "Did you kill Jane Doe?" then the person is telling the truth. If not, he or she is lying.

Despite its reputation as the default lie detector, the polygraph has never received much credibility. In 1922, a federal judge ruled that Marston's device could not be used in a murder case; it did not hold "general acceptance" among the scientific community, wrote Justice Josiah Alexander Van Orsdel of the United States Court of Appeals. This decision, known as the "Frye standard," has essentially kept the polygraph out of courtrooms ever since.

In 2002, the National Academy of Sciences orchestrated a massive review of the polygraph. The Academy concluded that the tool was not consistent enough to be used as a screening device when hiring national security employees. The physiological responses measured by the machine can be the result of many factors other than lying, including mere nervousness.

"There are many people who will speak in favor of the polygraph," says William Iacono, who is a professor of psychology and law at the University of Minnesota. "The argument is, if the government uses it 100,000 times a year, how can it be so wrong? The reason they believe it is because of the nature of the feedback they get. Occasionally, people fail the test and they're asked to confess, and they do. But if a guilty person passes, he doesn't turn around on his way out and say: ‘Hey, I really did it.' They never learn of their errors, so they don't think there are any errors."

In the end, Marston's reputation made out better than that of his machine; he went on to earn fame as the creator of Wonder Woman.

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