Lie detector
From Encyclopædia
Lie detector is the common name for the polygraph, an instrument used to record certain physiological changes that take place in response to questioning; these changes presumably indicate the truthfulness of the statements made by the person being questioned. The reliability of polygraphy depends heavily on the skill of the polygraph operator, who uses the instrument data as the basis for a judgment as to whether or not the test subject is telling the truth.Attempts to correlate blood
pressure and respiration rate with lying had been made since the late 19th century. The first practical polygraph was devised (1921) by John A. Larson, a medical student at the
university of California. His instrument gave a continuous recording of blood
pressure and respiration. Later, a technique was developed for measuring
stress-induced variations in the electrical conductivity of the
skin (galvanic
skin reflex, or GSR); and a single three-channel instrument combining Larson's device with a GSR mechanism was marketed in the 1930s by Leonarde Keeler. Keeler's instrument quickly gained acceptance for use in criminal interrogation and for personnel selection and theft
Control in commercial institutions. In recent years the Psychological
stress Analyzer--an instrument that measures
stress-induced changes in the tonal quality of the voice--has also come into wide use.Polygraph use has given rise to important civil liberties and legal questions--as well as the continuing question of reliability. In 1988, Congress prohibited private businesses from requiring workers and job applicants to take lie-detector tests, with some exceptions involving security services and employees suspected of financial crime. The law banning polygraphs does not apply to federal, state, or local governments. Courts of law generally deny the admissibility of polygraph
evidence except when agreed to by both defense and prosecution with the judge's concurrence.Robert F. BorkensteinBibliography: Abrams, Stan, The Complete Polygraph Handbook (1989); Block, Eugene B., Lie Detectors: Their History and Use (1977); Ferguson, Robert J., et al., Preemployment Polygraphy (1984); Gale, Anthony, ed., The Polygraph Test: Lies, Truth and
science (1988).
