Polygraphs

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A polygraph (commonly referred to as a lie detector) is an instrument that measures and records several physiological responses such as blood pressure, pulse, respiration and skin conductivity while the subject is asked and answers a series of questions, on the basis that false answers will produce distinctive measurements. The polygraph measures physiological changes caused by the sympathetic nervous system during questioning. Within the Federal Government, a polygraph examination is also referred to as a psychophysiological detection of deception (PDD) examination. Several other technologies are also used in the field of lie detection, but the polygraph is the most famous.

History

The idea that lying produces physical side-effects has long been claimed. In West Africa persons suspected of a crime were made to pass a bird's egg to one another. If a person broke the egg, then he or she was considered guilty, based on the idea that their nervousness was to blame. In ancient China the suspect held a handful of rice in his or her mouth during a prosecutor's speech. Since salivation was believed to cease at times of emotional anxiety, the person was considered guilty if by the end of that speech the rice remained dry.

Early devices for lie detection include an 1885 invention of Cesar Lombroso used to measure changes in blood pressure for police cases, a 1914 device by Vittorio Benussi used to measure breathing, and an abandoned project by American William Marston which used blood pressure and galvanic skin response to examine German prisoners of war.

A device recording both blood-pressure and galvanic skin response was invented in 1920 by Dr. John A. Larson of the University of California and first applied in law enforcement work by the Berkeley Police Department under its nationally renowned police chief August Vollmer. Further work on this device was done by Leonarde Keeler. The first time the term "polygraph" was used was in 1906 by James MacKenzie in his invention the "ink polygraph," which was used for medical reasons.

Read more at Wikipedia.org