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What Data Are Measured in Polygraph Tests? For centuries, humans have looked for a reliable method to distinguish lies. In very old Hindu and Chinese communities, authorities “detected” lies by making the subject to chew a grain of rice and spit it out. A dry grain of rice would indicate the dry mouth of a liar. In India, if rice adhered to the mouth, it would mean guilt. Though these methods were ancient and non-scientific, they however stressed the elementary theory humans make in lie detection: lying may be detected by observing physiological signs. Whenever a person lies or is asked a critical question, his heart may begin to race, increasing his blood pressure. As well, the test subject may also hold his breath, inhale a big one, or perspire. These physiological irregularities are caught by the polygraph for the polygraph examiner’s interpretation. It is the judgment of the examiner to equate the significant data changes with dishonesty. Cardiovascular Activity
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An encircling, air-filled cuff placed around the upper arm records blood pressure and heart rate. Changes in blood pressure affect the air pressure in the cuff. The polygraph machine records such changes and displays them on a computer screen, side by side with respiratory and perspiratory data.
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Respiration Two pneumograph devices, which capture changes in volume or movements in the thoracic cavity, record the subject’s respiration pattern while he breathes. One pneumograph tube goes around the chest while the other is strapped around the abdomen. Like the arm cuffs used to detect cardiovascular changes in a subject, the pneumograph tubes are also filled with air and connected to the machine. During inhalation and exhalation, the tubing air pressure changes, and each change will be reflected in the polygraph machine. Perspiration Sweat measurement, scientifically referred to as the measurement of galvanic skin resistance, is conducted by attaching a two-piece galvanometer to two fingertips of the subject. Through the galvanometer, a small electric current is sent into the skin from one fingerplate, and the amount of current that got through on the other fingerplate will be recorded. Dry skin conducts electricity poorly. However, during perspiration, water and salt from the sweat drives down skin resistance, allowing a bigger amount of electric current to flow on the surface of the skin. In other words, whatever amount of electric current is recorded by the galvanometer, indicates the amount of sweat that fingertips of the subject produced. Despite not being totally accurate, polygraph tests are constantly used by government authorities, especially law enforcement agencies, as an instructive tool. Through rapid technological advancements, humans will soon to strengthen the correlation between the psychological state of lying and its physiological indications.