A polygraph, or lie detector, is an instrument that attempts to determine whether a person is telling the truth by measuring and recording physiological changes in the body while the subject answers a series of questions. The word polygraph literally means “many writings” and comes from the fact that the instrument simultaneously records a number of different body responses, and the responses are graphically recorded. Polygraph tests are based on the theory that lying causes stress, which in turn causes physiological changes in the body. Sensors are attached to the body to mechanically record these changes (in breathing, blood pressure, pulse, and perspiration), which are then measured to indicate whether the subject of the exam is answering the questions truthfully. Polygraph use is controversial ...