History: History “For centuries, humans have sought a reliable means to detect lies. In ancient Hindu and Chinese civilizations, authorities “detected” lies by asking the suspect to chew a grain of rice and spit it out. In china, a dry grain of rice would be indicative of the dry mouth of a liar. In India, rice stuck to the mouth would be the sign of guilt. Although these methods were primitive and non-scientific, they nonetheless highlight the fundamental assumption humans make in lie detection: the psychological state of lying can be detected by physiological signs.”
How it works: How it works “Of the three physiological signs recorded in modern polygraphs, cardiovascular activity was the first sign to be associated with lying. This association was first documented by an Italian criminologist named Lombroso in the late nineteenth century. Lombroso noted an increase in a subjects blood pressure and heart rate when the subject was giving untruthful answers.”
PowerPoint Presentation: While Lombroso studied cardiovascular activity; Larson added respiratory activity to the polygraph. He based his theories off of studies done in the early 1910’s that had indicated that breathing patterns change when a person is being untruthful.
PowerPoint Presentation: “A third physiological channel used in modern polygraphs would be in added in the 1920s by Leonarde Keeler. Keeler assumed that a lying person would sweat more than a truthful person, which would decrease skin resistance due to a higher concentration of negatively charged chloride ions on the surface of the skin.”
PowerPoint Presentation: A polygraph works by using two electrodes that usually are attached to one hand to measure changes in electrical conductivity of the skin. (This measures how much we sweat.) A blood pressure cuff is then attached to the upper arm just as it would be in a physicians setting. The blood pressure cuff monitors changes in cardiovascular activity while recording the results. The polygrapher is also trained in detecting mannerisms closely associated with lying. Eye movement or fidgeting, or changes in tone of voice may all be linked. This is why the control is so important. Without knowing how the subject normally converses we cannot prove that they are lying. The subject must be comfortable during the control and not feel as if they are being interrogated.