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What Data Form the Basis of Results in Polygraph Tests? For hundreds of years, humans have pursued reliable methods of detecting 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 be associated with the dry mouth of a liar. In India, if rice stuck to the mouth, it would be a sign of guilt. Even if these methods were archaic and non-scientific, they nevertheless underscored the basic supposition humans make in lie detection: lying can be detected through physiological signs. Every time a person lies or is asked a delicate question, his heart may start to race, increasing the body’s blood pressure. Also, the test subject may also hold his breath, inhale a large one, or perspire. Such physiological irregularities are spotted by the polygraph and read by the polygraph examiner. It is the discretion of the examiner to associate the sudden data changes with dishonesty. Cardiovascular Activity
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To record blood pressure and heart rate, an encircling, air-filled cuff will be placed on the upper arm. When there are changes in blood pressure, the air pressure in the cuff changes as well. Such changes are recorded by the polygraph machine and then displayed on a computer monitor, together with respiratory and perspiratory data.
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Respiration The respiration pattern of a subject is recorded by two pneumograph devices capturing thoracic volume change or movement as a person breathes. One pneumograph tube is fastened around the abdomen and the other around the chest. 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 Perspiration measurement, known scientifically as the measurement of galvanic skin resistance, is conducted with the use of a two-piece galvanometer connected to two of the subject’s fingertips. 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 is a poor electricity conductor. 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. Hence, the amount of electric current the galvanometer records, is a reflection of how much sweat that was produced in fingertips of the subject. Although not completely accurate, polygraph tests are often used by as an instructive tool by government authorities and especially law enforcement agencies. With the advancements in technology, humans will be able to better connect the psychological state of lying with physiological manifestations.