IF you’re like most people, lying makes your heart race. It makes you pant. It drives up your blood pressure and makes you drip sweat. A polygraph machine detects lies by looking for signs of these physiological changes.
The goal of a lie detector is to see if the person is telling the truth or lying when answering certain questions.[ihc-hide-content ihc_mb_type=”show” ihc_mb_who=”2,3″ ihc_mb_template=”1″ ]
When a person takes a polygraph test, four to six sensors are attached to him. A polygraph is a machine in which the multiple (“poly”) signals from the sensors are recorded on a single strip of moving paper (“graph”). The sensors usually record: The person’s breathing rate, pulse, blood pressure and perspiration
Sometimes a polygraph will also record things like arm and leg movement.
When the polygraph test starts, the questioner asks three or four simple questions to establish the norms for the person’s signals. Then the real questions being tested by the polygraph are asked. Throughout questioning, all of the person’s signals are recorded on the moving paper.
Both during and after the test, a polygraph examiner can look at the graphs and can see whether the vital signs changed significantly on any of the questions. In general, a significant change (such as a faster heart rate, higher blood pressure, increased perspiration) indicates that the person is lying.
When a well-trained examiner uses a polygraph, he or she can detect lying with high accuracy. However, because the examiner’s interpretation is subjective and because different people react differently to lying, a polygraph test is not perfect and can be fooled.
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