Fictoid #8:
The Lie Detector

"US Congressman Gary Condit has passed a lie detector test in which he was asked if he had harmed missing Washington intern Chandra Levy," the BBC reported on July 13,2001, quoting his lawyer as saying "Mr Condit had been exonerated by the test." It was not surprising Congressman Condit would use a "lie detector" to to try to dispel suspicion. Lie detectors, or Polygraph machines, as they are also called, are used throughout the federal government by the FBI, Secret Service, CIA, Drug Enforcement Administration, National Security Agency, Department of Energy, Department of Defense, Bureau of Alcohol, Tobacco and Firearms, Defense Security Service, and the U.S. Marshall's Service. That they can detects lies, or exonerate a subject, is however a fictoid that has persisted in the media decades.

In his secret testimony before the Warren Commission in 1964, J. Edgar Hoover, said that the "polygraph, often referred to as a lie detector, is not in fact such a device." He explained that its value to law enforcement agents was as a tool of intimidation: if a subject believed the central deception that the machine could detect lies, he would have an incentive not to lie when strapped in the machine. More recently, in 1983, the Office of Technology Assessment concluded "the available research evidence does not establish the scientific validity of the polygraph test for personnel security screening." There are still no peer-reviewed tests using randomly distributed true and false answers. As recently as 2000, the U.S. Supreme Court, in a decision upholding the absolute ban on the use of polygraph tests in court-martial proceedings said, "There is simply no consensus that polygraph evidence is reliable." In fact, there is no epistemological basis for believing that the polygraph machine is even designed to detect lies. It measures emotional responses that can proceed from many factors including fear, anxiety and nervousness. Whether or not such emotions are connected to deception cannot be determined from the data.

Intelligence agencies know that the polygraph machine is not a lie-detector. If it actually worked, they would be out of the espionage business. since any mole that they recruited in enemy intelligence services would be revealed by a single polygraph test. But, as Aldrich Ames, and many other KGB moles in the CIA proved by lying without detection, this is not the case. The government agencies that use it— the FBI, CIA, Secret Service, NSA, DEA, Department of Energy (to examine thousands of scientists)-- while, aware that it is not a lie detector, use it for intimidation purposes.

Polygraphs are thus commonly designed but to deceive subjects by dazzling them with multiple sensors. The CIA's polygraph machine, for example, uses rubber hoses on both the chest and abdomen to measure changes in respiration, electrodes, which are attached to fingertips, to measure changes in sweat, skin temperature and vessel constriction and a blood pressure arm cuff to measure changes in the heart rate. If any of the three sensors were actually capable of measuring deception (which they are not), the other two devices would be redundant. But three sensors— a polygraph instead of a monograph— helps the deception by dazzling subjects. If only one sensor was used— say, for, example, a blood pressure cuff — subjects might focus on the issue of what blood pressure changes actually measure. Triple instruments make such a focus more difficult, which is why dazzling, or overloading the brain, is an effective technique in such deceptions.

The Fictoid persists in the media, as well as movies, because it appears to present a scientific solution to a vexing problem: telling truths from lies.

An entire organization, AntiPolygaph, is devoted to exposing this fiction.

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