Lie Detection Test refers to an examination which is based on an assumption that there is an interaction between the mind and body and is conducted by various components or the sensor s of a polygraph machine, which are attached to the body of the person who is interrogated by the expert. The machine records the blood pressure, pulse rate and respiration and muscle movements. Lie Detection Test is conducted in three phases- a pretest interview, chart recording and diagnosis. The examiner, usually a clinical or criminal psychologist prepares a set of test questions depending upon the relevant information about the case provided by the investigating officer, such as the criminal charges against the person and statements made by the suspect. The subject is questioned and the reactions are measured. A baseline is established by asking questions whose answers the investigators know. Lying by a suspect is accompanied by specific, perceptible physiological and behavioural changes and the sensors and a wave pattern in the graph expose this. Deviation from the baseline is taken as a sign of lie. All these reactions are corroborated with other evidence gathered. The Lie Detection Test was among the first scientific tests to be used by the interrogators.

It was Keeler who further refined the polygraph machine by adding a Psycho-galvanometer to record the electrical resistance of the skin.

Lie Detection Test is also called Polygraph Detection Test or Polygraph Test.

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