Derived from the Greek language, the term "polygraph" means "many writings". The name refers to the way in which certain physiological activities are continuously and simultaneously recorded.
A polygraph is a diagnostic instrument used by a polygraphist to collect, measure and record certain physiological activities when a person answers a series of questions about a specific event during a polygraph examination. This physiological data will be analyzed to determine if the person was telling the truth when answering the polygraph examination questions.
Sometimes a polygraphist may use a conventional instrument, also called an analog instrument. However, since the early 1990s, most polygraph examinations are administered using computerized polygraph instruments.
Conventional instruments record physiological reactions continuously and simultaneously in graphic form using ink pens on a moving paper roll.
The development of medical grade instrumentation and software has made it possible for computerized polygraphs to record physiological data directly to a software program and display the data on a computer screen. Graph analysis is done on a screen, rather than on a roll of paper, and can be printed as well.
During a polygraph examination, the polygraph detects, measures and records physiological data obtained from three major systems in the human body, each of which is controlled by the Autonomic Nervous System:
A) Cardiovascular system: Heart rate, blood pressure, blood volume.
B) Respiratory system: Respiratory activity.
C) Electrodermal system: Activity of the sweat glands.
The polygraph is used to detect and record human physiology. It is the job of the polygraphist to analyze, interpret and evaluate the physiological data obtained from the polygraph examination and then form a professional opinion as to the truthfulness of the statements made by a person based on the evaluation of these data.
The polygraph is often called the "lie detector".