how does the polygraph work?
• When a person perceives a threat, the body reacts to the threat. This is referred to as the “fight or flight” reaction, as the body readies itself either to fight off the threat or to flee. When a person tells a lie, it is because for some reason, the truth constitutes a threat to that person. Consequently, certain physiological reactions take place in the person’s body which he/she cannot control and which can be measured by the polygraph (See “Human physiology: a basis for the detection of deception” on our web site for more details). A polygraph instrument collects physiological data from at least three systems of the human body. Pneumograph tubes are placed over the examinee’s chest and abdominal area to record breathing patterns and finger plates are attached to the fingers to record sweat gland activity. A blood pressure cuff will record cardiovascular activity. The reactions are charted by the polygraph instrument and reflected on charts printed from the recordings.
