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A lie detector test measures a person’s physiological responses to questions to detect deception. It records breathing, sweating, and heart rate, and is used by law enforcement and employers. However, it can be manipulated and lead to erroneous results due to anxiety or subjective interpretation.
A lie detector test, also called a polygraph test, is a type of exam designed to uncover untruthful or deceptive behavior by using an instrument to measure a person’s involuntary responses to an examiner’s questions. Most lie detector tests work by attaching multiple sensors to a person’s body. As the person answers the examiner’s questions, sensors register the signals on a moving strip of paper. The signals measure the changing physiological responses when the subject is asked certain questions. These changes are recorded on a graph, which is subsequently analyzed by the examiner.
In general, a lie detector test records physiological data from different systems in a person’s body. Most tests record the person’s breathing, sweating, and heart rate. Some lie detector systems record blood pressure as well as arm and leg movements. Speech stress analysis is not usually part of a lie detector test.
Substantial changes in a person’s sensory responses typically indicate that the person is lying. For example, if a person’s heart rate increases when an examiner asks a certain question, the sensors detect it and record it on the graph. The examiner notes these changes as he analyzes the graph. Examiners who have had a good deal of training and experience are usually able to pick up on the signs of lying with a great degree of accuracy.
The lie detector test is often used by law enforcement when examining criminal suspects. Private employers also occasionally use lie detection systems when hiring prospective employees. For example, some government agencies, such as the Central Intelligence Agency (CIA) in the United States, require certain employees to undergo lie detector tests as a condition of employment.
A lie detector test can prove unreliable. Because the test records bodily responses, it can be manipulated to some extent. For example, a person may take sedatives to reduce nervous reactions before taking a test. A subject may even bite off certain areas of their mouth to produce a constant physiological response to questions and to prevent the machine from detecting changes in vital signs.
In some circumstances, a lie detector test can lead to erroneous results. For example, a person prone to anxiety may be extremely nervous during the test and thus skew the results. The way an examiner phrases questions can also lead to errors. Also, how an examiner interprets the results of a lie detector test is subjective and can lead to some inaccuracies.
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