Even though scientists question the accuracy of lie detectors, the CIA, FBI, and other federal agencies use polygraph machines to screen applicants and to hunt for lawbreakers. There are many researchers and defense attorneys who say polygraph is prone to a higher number of false results. Despite this it has emerged as a tool in the CIA’s effort to identify suspected leakers of government anti-terrorism tactics.
The polygraph machine measures various physiological changes such as blood pressure, respiratory rate, heart rate, and electro-dermal activity (sweat). The point is to determine when subjects are getting anxious. The idea is that deception involves an element of anxiety. The clincher is that an emotion (anxiety) can be triggered by many factors other than not telling the truth. As a result the experts feel that the tests can overlook smooth-talking liars while indicating innocent people who are simply rattled.
Polygraph tests results are generally inadmissible in federal courts and most state courts. On the other hand, statements or admissions made during the course of the test can be used in court. Some people seem to feel some of the polygraph’s value is in prompting people to tell the truth.
Questions which focus on whether people have memory of a certain event give far more reliable results than screening tests which rely on emotions triggered by a wide range of factors.
Polygraph examinations are designed to observe significant involuntary responses going on in the person’s body when that person is subjected to stress, such as the stress associated with deception. The exams are not capable of detecting if the person is lying.
How do liars beat the test? The exam is started out with baseline questions which provide the examiner with baseline physiologic responses. The liars simply increase their physiologic responses with exciting thoughts, altering one’s breathing pattern, or biting the side of their tongue. All these measures increase all the physiologic parameters that are being measured, thus providing these false numbers as their baseline. When later in the exam they tell a lie, these increased parameters are compared to the false baseline parameters and are viewed to be normal.
If you use the lie detector in your story, you may want to keep in mind how it is viewed, how it works, and how it can be beat. Lie detector results are not considered as valid by some and are not allowed in most courts. Remember that it cannot detect a lie, only if there is possible deception. And most of all, that the lie detector can be beat by someone who knows how.
Faye M. Tollison
Author of: To Tell the Truth
Upcoming books: The Bible Murders
Member of: Sisters in Crime
Writers on the Move