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Kunstformen der Natur (1904) by Ernst Haeckel
Kunstformen der Natur (1904) by Ernst Haeckel

A polygraph, popularly referred to as a lie detector, measures and records several physiological indices such as blood pressure, pulse, respiration, and skin conductivity while the subject is asked and answers a series of questions. The belief underpinning the use of the polygraph is that deceptive answers will produce physiological responses that can be differentiated from those associated with non-deceptive answers; the polygraph is one of several devices used for lie detection.

The polygraph was invented in 1921 by John Augustus Larson, a medical student at the University of California, Berkeley and a police officer of the Berkeley Police Department in Berkeley, California. The polygraph was on the Encyclopædia Britannica 2003 list of greatest inventions, described as inventions that "have had profound effects on human life for better or worse."

The efficacy of polygraphs is debated in the scientific community. In 2001, a significant fraction of the scientific community considered polygraphy to be pseudoscience. In 2002, a review by the National Academies of Science found that in populations untrained in countermeasures, polygraph testing can discriminate lying from truth telling at rates above chance, though below perfection. These results apply only to specific events and not to screening where it is assumed that polygraph would work less well. Effectiveness may also be worsened by countermeasures.

In some countries polygraphs are used as an interrogation tool with criminal suspects or candidates for sensitive public or private sector employment. US law enforcement and federal government agencies such as the FBI and the CIA and many police departments such as the LAPD use polygraph examinations to interrogate suspects and screen new employees. Within the US federal government, a polygraph examination is also referred to as a psychophysiological detection of deception (PDD) examination.

Polygraph testing is designed to analyze the physiological reactions of subjects. However, research has indicated that there is no specific physiological reaction associated with lying and that the brain activity and mechanisms associated with lying are unknown, making it difficult to identify factors that separate liars from truth tellers. Polygraph examiners also prefer to use their own individual scoring method, as opposed to computerized techniques, as they may more easily defend their own evaluations.

The validity of polygraph testing is again called in to question with the relevant-irrelevant testing technique, designed to gauge reactions of subjects against crime questions and other non-crime related questions. Studies have indicated that this questioning technique is not ideal, as many innocent subjects exert a heightened physiological reaction to the crime relevant questions.

The control question test, also known as the probable lie test, was developed to combat the issues with the relevant-irrelevant testing method. Although the relevant questions in the probable lie test are used to obtain a reaction from liars, it can also gain a reaction from the innocent subject who is afraid of false detection. The physiological reactions that "distinguish" liars, may also occur in individuals who fear a false detection, or feel passionately that they did not commit the crime. Therefore, although a physiological reaction may be occurring, the reasoning behind the response may be different. Further examination of the probable lie test has indicated that it is biased against innocent subjects. Those who are unable to think of a lie related to the relevant question, will automatically fail the test.

Polygraph examiners, or polygraphers, are licensed or regulated in some jurisdictions. The American Polygraph Association sets standards for courses of training of polygraph operators, though it does not certify individual examiners.



Earlier societies utilized elaborate methods of lie detection which mainly involved torture; for instance, the Middle Ages used boiling water to detect liars as it was believed honest men would withstand it better than liars. Early devices for lie detection include an 1895 invention of Cesare Lombroso used to measure changes in blood pressure for police cases, a 1904 device by Vittorio Benussi used to measure breathing, and an abandoned project by American William Moulton Marston which used blood pressure to examine German prisoners of war (POWs). Marston’s machine indicated a strong positive correlation between systolic blood pressure and lying.

Marston 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. Marston's main inspiration for the device was his wife, Elizabeth Holloway Marston. "According to Marston’s son, it was his mother Elizabeth, Marston’s wife, who suggested to him that 'When she got mad or excited, her blood pressure seemed to climb'" (Lamb, 2001). Although Elizabeth is not listed as Marston’s collaborator in his early work, Lamb, Matte (1996), and others refer directly and indirectly to Elizabeth’s work on her husband’s deception research. She also appears in a picture taken in his polygraph laboratory in the 1920s (reproduced in Marston, 1938)."

Despite his predecessor's contributions, Marston styled himself the "father of the polygraph" . Marston remained the device's primary advocate, 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. In 1938 he appeared in advertising by the Gillette company claiming that the polygraph showed Gillette razors were better than the competition.

A device recording both blood pressure and breathing was invented in 1921 by Dr. John Augustus 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. As Larson's protege, Keeler updated the device by making it portable and added the galvanic skin response to it in 1939. His device was then purchased by the FBI, and served as the prototype of the modern polygraph.

Several devices similar to Keeler's polygraph version included the Berkeley Psychograph, a blood pressure-pulse-respiration recorder developed by C. D. Lee in 1936 and the Darrow Behavior Research Photopolygraph, which was developed and intended solely for behavior research experiments.

A device which recorded muscular activity accompanying changes in blood pressure was developed in 1945 by John E. Reid, who claimed that greater accuracy could be obtained by making these recordings simultaneously with standard blood pressure-pulse-respiration recordings.

Notable cases

Polygraphy has been faulted for failing to trap known spies such as double-agent Aldrich Ames, who passed two polygraph tests while spying for the Soviet Union.

See also

See also

The polygraph shoul dnot be used as a means to discover truth, but as a machine to coherse victims into confessing even when they are not guilty.

Unless indicated otherwise, the text in this article is either based on Wikipedia article "Polygraph" or another language Wikipedia page thereof used under the terms of the GNU Free Documentation License; or on original research by Jahsonic and friends. See Art and Popular Culture's copyright notice.

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