What is a Polygraph?
The term polygraph means many writings. The name refers to the manner in which selected physiological activities are simultaneously collected and recorded. The polygraph is like a recorder, except instead of recording sounds, the polygraph instrument will record physiological changes occurring within the examinee’s body as the polygraph examiner asks a series of test questions. The polygraph instrument is basically a combination of medical devices that are used to monitor changes occurring within the examinee’s body. As an examinee is questioned about a certain event or incident, the examiner records and monitors the relative changes in the examinees heart rate, blood pressure, respiratory rate, and electro-dermal activities.
The term “polygraph” literally means “many writings”. The name refers to the manner in which selected physiological activities are simultaneously recorded. Polygraph examiners may use conventional instruments, sometimes referred to as analog instruments, or computerized polygraph instruments. It is important to understand what a polygraph examination entails. A polygraph instrument will collect physiological data from at least three systems in the human body. A typical polygraph examination will include a period referred to as a pre-test, a chart collection phase and a test data analysis phase. In the pre-test, the polygraph examiner will complete required paperwork and talk with the examinee about the test. During this period the examiner will discuss the questions to be asked and familiarize the examinee with the testing procedure. During the chart collection phase the examiner will administer and collect a number of polygraph charts. Following this, the examiner will analyze the cha
The polygraph measures predictable changes in a person’s body that are associated with the stress of deception. These changes include alterations in heart rate, breathing, and electrodermal activity (emotional sweating). Many other changes occur as well: the pupils get larger, digestion slows, the body’s blood supply is redistributed away from the skin and gastrointestinal regions and toward the muscles, etc. The measures used by the polygraph were selected in the 1920’s and 1930’s because they were simple to record (as opposed to brain waves or gastrointestinal activity), they were sensitive (even minor changes in stress levels caused these physiological changes to occur), and they were accurate.
