Lie detector is a device that helps determine whether a person is telling the truth. It is also called a polygraph. A lie detector records physical changes that occur in the body as a person answers questions. Such changes include alterations in the blood pressure, pulse rate, perspiration, and respiration that may occur when an individual lies. These changes are caused by the person’s emotional response to telling a lie.
Lie detectors help police and other investigators question suspects about their possible involvement in a crime. They are also used to screen applicants for sensitive jobs, such as positions with law enforcement or intelligence agencies. The Employee Polygraph Protection Act (1988) does not permit most nongovernment employers to administer lie detector tests to employees.
A person who agrees to take a lie detector test sits in a chair while answering a series of “yes or no” questions. The lie detector records the changes in the person’s body functions by drawing lines on a moving graph. A lie detector examiner interprets the test results. The effectiveness of a lie detector test depends on a number of variables. These include the types of questions, the manner in which they are asked, and the training and experience of the examiner. Some of the questions asked during a lie detector test are related to the matter being investigated. Others are unrelated or only slightly related. They are included to improve the test’s accuracy. If a person lies, the graph normally shows a change in one or more of the body functions being recorded.
The United States Supreme Court ruled in United States v. Scheffer (1998) that the results of lie detector tests may be banned in military courts. But the decision of whether to accept lie detector results as evidence is left up to individual jurisdictions. Some states, for example, ban their use in court. In others, lie detector test results may be used as evidence if all parties involved in a case agree beforehand to their use. The evidence must also meet certain scientific standards. No defendant or witness may be forced to take a lie detector test.
Many legal experts believe that testimony obtained by using lie detectors is not accurate enough to be used in court. Some also say that such testimony may violate the Fifth Amendment to the Constitution. The Fifth Amendment protects people from testifying against themselves.
John A. Larson, a California police officer with a doctorate in physiology, developed one of the first lie detectors in 1921. In 1966, a number of lie detector organizations joined to form the American Polygraph Association. The association helps supervise the use of lie detectors and establishes qualifications for the examiners.
