Polygraphs

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. more...

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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.

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.

The origins of the modern polygraph date to 1913, when William Moulton Marston, a psychology student at Harvard University, used the systolic blood-pressure test as a method of lie detection. He wrote a second paper on the concept in 1915, when finishing his undergraduate studies. He entered Harvard Law School and graduated in 1918, re-publishing his earlier work in 1917. A more complex device recording both blood-pressure and galvanic skin response was invented 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. The first time the term "polygraph" was used was in 1908 by James MacKenzie in his invention the "ink polygraph," which was used for medical reasons.

Marston nevertheless remained the device's primary advocate, endlessly lobbying for its use in the courts. In 1938 he published a book, The Lie Detector Test, wherein he documented the theory and use of the device. Nevertheless he was not above a little faked publicity, and in 1938 appeared in advertising by the Gillette company claiming that the polygraph showed Gillette razors were better than the competition.

Testing Procedure

Today, polygraph examiners use two types of instrumentation, analog and computerized. In the United States, most examiners now use computerized instrumentation.

Read more at Wikipedia.org