The “lie-detector” also called as polygraph machine which can detect lies. An earlier and less successful lie detector or polygraph machine was invented by James Mackenzie in 1902. Later John Larson, a University of California medical student, invented the Modern lie detector (Polygraph) in 1921.Commonly used in criminal interrogation and investigations since 1924.The lie detector is still controversial among psychologists, and is not always judicially acceptable.This device actually measures nervous excitement. It operates on the premise that if a person is telling the truth they will remain calm.
Does the polygraph work?
There has been a lot of controversy about whether lie detectors work. Some experts claimed that a high proportion of persons who “failed” the polygraph subsequently confessed to crimes. On the other hand, the test generates a lot of false positives, i.e., people who are telling the truth but whose polygraph test suggests they are lying.The main theory is that when a person lies, the laying causes a certain amount of stress that produce changes in several involuntary physiological reactions.A series of different sensors are attached to the body , and as the polygraph measures change in breathing, blood pressure, pulse and perspiration, pen record that data on graph paper.During a lie detector test, the operator asks a series of control questions that set the pattern of how an individual responds when giving true and false answers. Then the actual questions are asked, mixed in the filler questions.The examination lasts about 2 hours, after which the experts interprets the data.
Interestingly, the polygraph is quite good at identifying liars but does no better than chance at detecting honest people according to Lykken. In other words, there is a 50:50 chance that a polygraph test will say an honest person is lying (a 50 percent “false positive” rate).
