The polygraph (popularly referred to as a lie detector) is an instrument that measures and records several physiological responses such as blood pressure, pulse, respiration, and skin conductivity while the subject is asked and answers a series of questions. When conducted by a competent and experienced polygraph examiner, deceptive answers will produce physiological responses that can be differentiated from those associated with non-deceptive answers.
At the outset, the examiner obtains a complete background information on the case. The polygraph test or examination proper consists of 3 phases.During the first phase, the pre-test phase, the examiner discusses with the subject the test issue, thoroughly reviews all of the test questions that will be asked during the test, and assesses the subject’s emotional and physiological suitability to undergo the polygraph test.
The testing phase consists of a series of tests where the subject’s physiological responses are recorded as the subject answers a set of questions reviewed earlier. The polygraph theory, is based on psychophysiological principle, is that when the subject hears a question which he or she intends to lie, the brain interpreters and triggers automatic and uncontrollable physiological changes captured by the polygraph.
During the post-test phase, the examiner reviews all test data obtained and interprets the polygraph charts, from which the examiner will reach one of 3 conclusions – that the subject is telling the truth; that the subject is not telling the truth; or that the results are inconclusive. Upon completion of the test a verbal report will be given to the client, followed by a written report which consists of a synopsis of the case information, a list of the relevant test questions, the subject’s answers, and the examiner’s opinion as to the subject’s truthfulness or deception.
Polygraph tests are strictly voluntary in nature and do not violate a subject’s human rights. Each polygraph test normally lasts between 2 to 3 hours.