The Polygraph Instrument

The polygraph machine or "lie detector" is an instrument or device that produces recordings of physiological phenomena that could be used to diagnose the truth or deception using a reliable technique. There are no specific physiological reaction linked to lying. The instrument can only record the physiological phenomena/changes that occur when the subject is deceptive. It cannot detect lies or deception. The examiner simply uses the instrument to attempt to detect deception.

Two Kinds of Polygraph Instrument

Most polygraph machines measure four to six physiological reactions that are recorded by three different medical instruments that are combined into one machine.

The Four Major Components of the Polygraph Instrument

The polygraph instrument is composed of four major parts: the pneumograph, the galvanograph, the cardiosphygmograph, and the kymograph. These components work simultaneously and help in the administration of the examination.

Tripod Foundation of Polygraph Technique

The two main sources of evidence relevant to the validity of polygraph testing are basic scientific knowledge about the processes the polygraph measures and the factors influencing those processes and applied research that evaluates the criterion validity of polygraph tests in specific settings. The following are the foundations of the polygraph technique that will help establish the relationship between the responses and the examination on the subject:

• Mechanical Leg Basic Premises The polygraph machine is capable of producing graphical records containing reliable information about physiological changes.

• Physiological Leg Basic Premises Physiological changes that occur automatically only after stimulation of a specific nervous system component

• Psychological Leg Basic Premises The specific nervous system component whose stimulation can thus be diagnosed is thus stimulated by the involuntary mental and emotional processes of the individual who is consciously attempting concealment of deceptions