The Polygraph Machine

Polygraph

Elephants cannot swim. How can you tell if I'm telling the truth? You can tell by testing me with a polygraph machine. Since civilization began, people have wanted a way to tell fact from fiction. In the middle ages, Europeans used torture because they thought that if you stress and hurt the body enough, it would cause a person who was lying to tell the truth. What this method has in common with today's lie detector, or polygraph, is that there is an involuntary physical response from a person when they are lying. The polygraph has a story of its own, but you'll have to decide for yourself if it is true or not. That story includes: how it was made, how it is used, and whether or not it works.

The polygraph machine is made of three main parts that are all made by different people. The first scientific instrument was used to measure physiological responses to lying was in 1895 when Italian psychiatrist, and criminologist Cesare Lombromso modified a preexisting piece of equipment to measure the physiological changes that occurred in the blood pressure and pulse rate of a crime suspect during a police interrogation. In 1921, a Canadian psychologist, John Larson, developed what many people think of as the original lie detector when he used both respiration rate and blood pressure. He named this device the polygraph. Several years later, in 1938, Leonard Keeler added the third physiological measuring component of the lie detector creating the polygraph we know today. This last device is called the psycho-galvanometer, and it measures the changes in the amount of galvanic activity, or sweat from a person. Once completed, the polygraph machine had many uses.

The polygraph test consists of many steps, it even includes a pretest. Before taking a polygraph test, the examiner asks the examinee several control questions to understand how the examinee responds to questions, and to help detect if he or she is lying during the actual polygraph test. This is important because the examiner will analyze the test afterwards to decide if the examinee was lying or not. Questions that would have special meaning to the criminal but not to others are often used. During a test usually only 3 out of 10 questions are relevant. The other questions are known as controls. Setting up a polygraph requires several different parts. In order to record changes in blood pressure and heart rate, an arm-encircling cuff is placed on the upper arm.