Lie detector

The National Investigation Agency on Monday got permission from a Delhi court to conduct a lie detector test on LeT terrorist Mohammed Naved Yakub, who was captured by villagers after an attack on a BSF bus in Udhampur earlier this month which had left two of its personnel dead.

A polygraph, popularly referred to as a lie detector, measures and records several physiological indices such as blood pressure, pulse, respiration, and skin conductivity while the subject is asked and answers a series of questions.[1] The belief underpinning the use of the polygraph is that deceptive answers will produce physiological responses that can be differentiated from those associated with non-deceptive answers; the polygraph is one of several devices used for lie detection.

The polygraph was invented in 1921 by John Augustus Larson, a medical student at the University of California at Berkeleyand a police officer of the Berkeley Police Department in Berkeley, California.[2] The polygraph was on the Encyclopædia Britannica 2003 list of greatest inventions, described as inventions that "have had profound effects on human life for better or worse."[3]

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, informs howstuffworks.com.

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.