Polygraph examiners, also known as Forensic Psycho-physiologists, administer polygraph tests. First there is a pre-test interview with the person concerned to establish the reason for the test, then personal particulars and medical histories are obtained to ensure suitability for the test.
People are generally not good at picking up when another person is lying, unless trained to know what to look out for. Facial and body movements, as well as conversation, offer clues as to whether a person is lying or not. None of these clues is foolproof, but they may provide some insight when investigators interrogate possible crime suspects. Polygraph testing is very controversial but there is a growing demand for it in the South African corporate world. The polygraph examiner observes the examinee for visual, verbal and behavioural cues which may expose a subtle lie, and take these observations into account when considering the result of the polygraph test.
The way the polygraph works is loosely based on the physiological changes the human body undergoes when a person is telling a lie. These reactions are then digitally recorded and interpreted by a qualified polygraph examiner. The changes in the human body are controlled by the autonomic or involuntary nervous system. What makes the autonomic nervous system so useful to an examiner conducting a polygraph test is that the person being tested is unable to control these reactions.
When a person is telling a lie, their body perceives the person being lied to as a threat and it will then enter the “fight or flight” mode, producing adrenalin. The person’s heart beats more rapidly, the pupils of the eyes dilate and the hands and fingers sweat. All these changes occur naturally to enable the person to strike harder, sprint faster or lift heavier loads, in order to escape threatening situations.
The polygraph device records all these reactions through four channels. A blood pressure cuff placed on the upper arm measures changes in blood volume. A sensor placed on the tip of a finger determines whether there is more sweat gland activity. Two sensors running across the chest and stomach also measure changes in the breathing pattern of the examinee. Some examiners use an additional sensor, which focuses on the eye and records changes in the size of the pupil.
The questions asked by a polygraph examiner are a combination of so-called “relevant” questions and “control questions”, for example about an office burglary. A person not involved in the burglary will show a strong physiological response to a question unrelated to the case under investigation, yet show no response to the relevant questions asked. The culprit, however, perceiving a relevant question, “were you involved in the burglary at your offices?” to be the more of a threat than the control question, would show a marked response when confronted with this direct query.
Whether polygraph tests are considered to be accurate or not, depends on who you ask. Those in favour of such tests claim that the new computerised polygraph systems are almost 100% accurate. Those opposed to polygraphs point out that the general consensus amongst scientists is that using the results obtained from polygraphs is not a scientific basis for determining guilt.
Polygraph testing in South Africat is still in its infancy. At this stage, there is no legislation controlling the use of the test, nor is there legislation protecting an employee’s rights against abuse of the test results obtained. Polygraph examiners have been accepted as expert witnesses.
A polygraph examiner will conduct four to five tests a day on average, go to clients, get case information and either conduct tests in the office or at a client’s premises. They also have to type reports, obtain statements and may be called upon to testify in court.