The Polygraph which is often referred to as a “Lie Detector” is an instrument that records physiological reactions caused by the autonomic nervous system. A polygraph examination is a combination of both a psychophysiological testing technique and an interview. The instrument itself is a combination of several recording devices routinely used in the medical and scientific community and it records the physiological changes responses which occur when the subject is asked questions during the test. The polygraph records respiration, cardiovascular activity and electro dermal activity.
- The first phase is the pre-test interview, which includes; obtaining a statement of consent to conduct the test; the completion of a medical questionnaire; an explanation of the equipment; obtaining background data from the examinee and their version of events. During this period, the examiner will discuss the questions to be asked and familiarize the examinee with the testing procedure All test questions are thoroughly reviewed giving the examinee an opportunity to qualify or explain any of their answers
- The next phase is the collection of data and initially consists of the attaching of the components which routinely includes breathing tubes which are attached around the examinee upper and lower chest area. These tubes record breathing rate, breathing volume and breathing pattern. A standard blood pressure cuff is attached to the examinees upper arm and is inflated to a light pressure immediately prior to the commencement of the test, to record a constant reading of the examinees heart rate and pulse rate; the pressure is then released at the end of the test. Electrodermal activity finger cuffs are attached to two fingers to measure skin conductance (sweat gland activity) and a photo-plethysmograph is attached to another finger to measure blood rate volume. The examinee will be seated on a sensor movement mat. Following this, the examiner will analyse the charts and render an opinion as to the truthfulness of the person taking the test. The examiner, when appropriate, will offer the examinee an opportunity to explain physiological responses in relation to one or more questions asked during the test. It is important to note that a polygraph does not include the analysis of physiology associated with the voice. Instruments that claim to record voice stress are not polygraphs and have not been shown to have scientific support
- Chart analysis and post-test interview
In most cases it is easy for a qualified examiner to determine if an examinee is attempting to alter the outcome of a test. When such behaviour is identified, a result of “purposeful non cooperation” is given.
Additionally it is beneficial to look for a polygraph examiner who has professional affiliations and memberships with recognised associations that set professional standards for its members, such as the American Polygraph Association or the British Polygraph Association. Currently there is no Irish Polygraph Association.