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Do Lie Detectors Work?
A polygraph reads many physical changes at the same time, it does not detect lies.
Credit: Gabriel Rodr

When candidates square off in debates, the truth seems to get stretched at least a few times, at minimum.

Now two politicians vying for an Indiana congressional seat say they'll be hooked up to polygraphs, or lie detectors, during a debate. But will it work?

Lie detectors have a long and controversial history.

The thinking goes, apparently, that pulling the truth out of Washington types takes savvy technology. But a polygraph is not actually a lie detector.

The term "polygraph" means "many writings" and refers to the fact that polygraph devices measure many physiological changes simultaneously.

Rather than alerting authorities when said person blurts out untruthful information, polygraphs detect physiological changes linked with lying in some people. To do this, a polygraph monitors, apparently with high accuracy, respiratory rate, heart rate, blood pressure and electrodermal response (a method to detect tiny changes in perspiration, usually from the fingertips).

In 2002, a study by the National Academy of Sciences revealed that "polygraph tests can discriminate lying from truth telling at rates well above chance, though well below perfection." The Academy scientists reported the polygraph "rests on weak scientific underpinnings despite nearly a century of study."

In addition, polygraphs have a high rate of false positives, in which the detector calls out an actual truth as a lie.

Some alternative ways of outing a liar include brain scans using functional MRI, which highlight regions of the brain with high blood flow (considered active regions). And recently, researchers have pinpointed certain brain areas linked with telling lies. Neuroscientists disagree on the usefulness of fMRI as a lie-detecting tool. Some have doubts on interpretations of fMRI results and others are iffy about the legality and ethics of invading a person's thoughts with brain imaging, according to scientists who attended a 2007 symposium entitled "Is There Science Underlying Truth Detection," hosted by the American Academy of Arts and Sciences.

Perhaps the human belly would be a better truth-meter than the brain or heart. A past study showed that telling lies gets the juices flowing in a person's stomach and "electrogastrograms" can pick up these gastric changes.

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