General Principle of the Use of Lie Detector Tests

Lie-detector tests can be used effectively in law enforcement.

Determining whether someone is telling the truth can be a difficult yet essential part of police procedure. Multiple forms of lie detection exist, some of which are used effectively in law enforcement.

Polygraph

The most familiar type of lie detector is the polygraph, an electronic machine that measures changes in various body systems to assess if an individual is telling the truth. The polygraph, when used by trained experts, is considered an accurate and effective measure of veracity.

Measurement

The polygraph measures changes in breathing, heart rate, blood pressure and sweat glands. The general theory is that the nervous system has an automatic response to stress that can be measured through physiological changes. The guiding assumption is that lying is stressful, and the body will react accordingly.

Interpretation

The crucial element of any polygraph is ensuring it is interpreted by a trained evaluator. The polygraph will indicate when there are physiological changes; it is up to the administrator of the test to assign meaning to those changes. Question selection is critical, as is pre-test screening to develop a baseline. The administrator of a polygraph must be able to distinguish between natural stress in response to the situation and the stress associated with telling a lie.

Additional types

There are additional lie-detection methods that are less common than the polygraph. A computer voice-stress analyzer measures vocal tremors that are said to be associated with increased stress. Pupillometrics is the study of changes in blinking and pupil dilation that can indicate whether an individual is telling a lie. Hypnosis and narcoanalysis, the use of drugs to assess truth, are other potential means of lie detection.

References

• Changing Minds: Lie Detectors
• Austin Peay State University: Police Lie Detection Procedures