Mr. Herndon. On the current polygraph used throughout the field the instrument records three different physiological responses.
Mr. Specter. And would you identify those three physiological responses, please?
Mr. Herndon. The first physiological response recorded on the polygraph pertains to the pneumograph tracing, pneumo pertains to the respiratory pattern of an individual. In other words, it records the inhalation and exhalation tracings of the person as he is normally breathing. It also records what we call the respiratory ratio, the ratio of the inhalation stroke to the exhalation stroke.
The second component utilized in the polygraph technique today is generally called the psychogalvanic skin response.
Mr. Specter. Spell that, please.
Mr. Herndon. Actually, it is referred to as the galvanic skin response, galvanic. This particular response is obtained by electrodes placed on the examinee’s hands or fingers, a small minute amount of electrical current is passed through the skin, and the galvanometer will record the minute changes in the electrical skin resistance of the skin or the electrodermal response.
The third component utilized in polygraph technique is the cardiograph. This particular component measures the relative blood pressure changes and also the changes in the heart rate or pulse beat. The tracing is obtained by a pneumatic cuff being placed on the arm, usually the left arm, a certain amount of pressure applied so that the mean blood pressure can be obtained and the tracing is recorded on a moving sheet of chart paper.
Mr. Specter. Would you outline briefly the development of the polygraph instrument, please?
Mr. Herndon. Over the years psychologists and physiologists have been aware of the fact that many people seem to respond physiologically under emotional stress, one, of course, being under a stress of a deception.
The more serious lie a person tells, quite frequently he is likely to have a physiological response. Over the years people who have dealt with interrogation techniques have frequently noticed that when a person is deceiving, that they visibly respond emotionally. In other words, they may not look a person right in the eye.