Lie detector( Polygraph)

1016 Words5 Pages
Lie Detector Specific Purpose: To inform my audience all about the lie detector. Central Idea: The lie detector is used in our society to detect deceit and lies. Introduction: In West Africa persons suspected of a crime were made to pass a bird's egg to one another. If a person broke the egg, then he or she was considered guilty, based on the idea that their nervousness was to blame. In ancient China the suspect held a handful of rice in his or her mouth during a prosecutor's speech. Since salivation was believed to cease at times of emotional anxiety, the person was considered guilty if by the end of that speech the rice was dry (Wikipedia). These days we use a lie detector to detect physiological irregularities when asking a person certain questions about an event or incident. I. The lie detector is more commonly known as the polygraph and was made in 1921 by John. A Larson. This machine was first used in law enforcement work by the Berkley Police Department (Bellis). The theory is that when a person lies, the lying causes a certain amount of stress that produces changes in several involuntary physiological reactions. By asking questions about a particular issue under investigation and examining a subject's physiological reactions to those questions, a polygraph examiner can determine if deceptive behavior is being demonstrated (Bellis).Simply put, whether the subject is lying or not. II. The polygraph measures respiratory rate, sweatiness of the finger tips, and blood pressure. Some parts of the polygraph used to measure these physiological reactions are pneumographs, galvanometers, and blood pressure cuffs. A. Respiratory rate - Two pneumographs, rubber tubes filled with air, are placed around the test subject's chest and abdomen. When the chest expands, the air inside the tube is displaced. In an analog polygraph, the displaced air acts on a
Open Document