Polygraph Collects data from 2 pneumo tubes applied around the subject’s upper chest and stomach and the blood pressure cuff attached to the subjects upper left arm. Set of two fingerplate electrodes measure galvanic skin resistance are fitted to two fingertips of the right hand. Subject must sit still and not move to ensure the accuracy of data collected.

BIO-FEEDBACK POLYGRAPHS

A polygraph 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, on the basis that false answers will produce distinctive measurements. The polygraph measures physiological changes caused by the sympathetic nervous system during questioning (Wikipedia, 2008). Most humans have five senses from which messages are sent to the brain. If any threatening message is received by the brain via any of these senses, the autonomic nervous system activates a defence mode for the human to protect itself. This is also known as the fight or flight syndrome. This causes some physiological changes to take place in the human body such as a faster heart rate, changes in blood pressure; they will inhale additional oxygen and there will be an increase in sweat gland activity. The same changes will take place in any circumstance where a human experiences a threat and makes a decision what to do in order to attempt to protect him/herself. When a person is asked a question, about a crime or activity, of which he is well aware via his memory that he is guilty, a fight or flight syndrome response could be activated to tell a lie in order to protect him/herself. If the question did not threaten the person, the necessity to lie would not have been an option as an innocent person would have simply told the truth. The strong focus of the human being is to survive and therefore the fear of being caught out lying threatens your immediate well-being. The function of the polygraph instrument is to make use of physiological responses visible for analysing. The polygraph instrument records four major responses: 1. Thoratic respiration (chest). 2. Abdominal respiration (stomach). 3. Electro dermal activity (sweating). 4. Cardio vascular responses (relative blood pressure). The innocent person will naturally always be tense, because of the unfamiliar circumstances he finds himself in. The fact that he is being investigated, that he does not know the polygraphist, that he does not know how capable the polygraphist is and the fact that he does not know how the polygraph works all contribute to nervousness. Therefore the innocent person's physiological responses will be greater than normal, but will stay on equilibrium. This condition is also referred to as general nervous tension. The innocent person will not show significant and consistent physiological changes towards the relevant (target) questions on the test. The guilty person will focus all his attention to the questions on which he has fear of detection of deception. This will cause the fight or flight syndrome, which will cause significant and consistent physiological changes towards the target questions.