lie detector

lie detector, instrument designed to record bodily changes resulting from the telling of a lie. Cesare Lombroso, in 1895, was the first to utilize such an instrument, but it was not until 1914 and 1915 that Vittorio Benussi, Harold Burtt, and, above all, William Marston produced devices establishing correlation of blood pressure and respiratory changes with lying. In 1921 an instrument capable of continuously recording blood pressure, respiration, and pulse rate was devised by John Larson. This was followed by the polygraph (1926) of Leonarde Keeler, a refinement of earlier devices, and by the psychogalvanometer (1936) of Walter Summers, a machine that measures electrical changes on the skin. A more recent innovation is a device, developed in 1970, called the psychological stress evaluator, which measures voice frequencies from tape recordings. Although the lie detector is used in police work, the similarity of physical changes caused by emotional factors such as feelings of guilt to those caused by lies has made its evidence for the most part legally unacceptable. An assessment of such devices by National Research Council (an arm of the National Academy of Sciences) found that they also were too unreliable to be used in screening for national security purposes, but they are widely used for such purposes nonetheless, sometimes with inconsistent results from one government agency to another. The use of lie detectors to screen employees and job applicants is highly controversial.

Bibliography

See E. B. Block Lie Detectors, Their History and Use (1977); C. Gugas The Silent Witness (1979); D. T. Lykken, A Tremor in the Blood (1981).

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lie detector

 or polygraph

Instrument for recording physiological phenomena (including blood pressure, pulse rate, and respiration) of a human subject as he or she answers questions asked by an operator. These data (recorded as graphs) are used as the basis for judging whether the subject is lying. The phenomena usually chosen for recording are those not easily controlled voluntarily. The types of questions asked, their wording, and the mode of presentation have a tremendous effect on the results and their reliability. Used in police interrogation and investigation since 1924, the lie detector is still controversial among psychologists and not always accepted as evidence in courts.

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lie detector [′lī dī‚tek·tər]

(engineering)

An instrument that indicates or records one or more functional variables of a person's body while the person undergoes the emotional stress associated with a lie. Also known as polygraph; psychintegroammeter.