There was a story about a little wooden puppet whose nose grew every time he told a lie. As the number of lies continued to grow so did his nose. This little puppet was named Pinocchio. As the story of the little puppet spread throughout time so did the myth that lie detector tests (also known as polygraph tests) measured the perfect indicators of lying through physiological and behavioral responses like how Pinocchio had shown through the growth of his nose. People are all too familiar with the lie detector tests, the media uses them constantly in their movies and television shows. The problem with this is that polygraph tests aren't 100% accurate when it comes to determining a guilty person from an innocent person. These tests measure the blood pressure, respiration, and skin conductance of the person that is being tested. There is a heightened autonomic activity in the body due to anxiety and the people being questioned are asked a series of questions that are relevant or irrelevant to the crime, and controlled. When a person is asked a question that is relevant to the crime and their autonomic activity level is high they are then labelled as deceptive because their autonomic response to the other questions were low, where if a person's activity level after a relevant question came up low they would be labelled as truthful.
Research studies have found that the polygraph test yields a high rate of false postives, meaning that a high number of innocent people are often labelled as guilty, and that the test often confuses responses of arousal with evidence of guilt. Researchers have made the comment that the detector has been misnamed and should be called the "arousal detector". Not only does the polygraph yield a high false positive rate but it also yields a high number of false negatives. People that are guilty have learned to beat the test, and therefore are labelled as innocent. The people who have learned to beat the test have done so by using countermeasures - methods designed to alter their responses to control questions. Finally, researchers have stated after proving the confusion of arousal and evidence of guilt that there is no such thing as the Pinocchio response.
The truth comes out about lie detector tests! I believe the use of these tests have no place in placing guilt on a person. There are definitely ways to hide true bodily responses. Although a bad example, in Oceans 13 one of the criminals has a electric pulse type gadget that masks his emotions and arousal. Against the most hardened criminals the test has to be ineffective because they know ways to beat it.