How does a lie detector work?
Are lie detectors efficient in detecting lies? The concept of a lie detector is centuries old. The ancient Chinese had a suspect chew dry rice while he was being questioned. After questioning, the rice was examined. If it was dry, the suspect was assumed to be guilty. As was assumed then and is currently supported by more recent evidence the nervous tension created by lying slowed or blocked the flow of saliva. Thus, the dry mouth lead to dry rice and a guilty verdict. The modern lie detector the polygraph does not use dry rice. (“Poly-” means “many,” and “graph” refers to “something that writes or records.”) The polygraph records several different activities at the same time. Typically it involves a pneumograph, a sphygmomanometer and the galvanic skin response. The pneumograph (“NEW-mow-graf”) involves a hose, which is pleated like an accordion, that is put around the suspect’s chest. It records the depth and rate of respiration. The sphygmomanometer (“SFIG-mow-meh-NOM-eh-ter”) is me
A polygraph (commonly yet incorrectly referred to as a lie detector) is a device that measures and records several physiological variables such as blood pressure, pulse, respiration and skin conductivity while the subject is asked and answers a series of questions. The measurements are posited to be indicators of anxiety that accompanies the telling of lies. Thus, measured anxiety is equated with telling untruths. However, if the subject exhibits anxiety for other reasons, or can control his anxiety level voluntarily, a measured response can result in unreliable conclusions. A polygraph test is also questionably used as a psychophysiological detection of deception (PDD) examination. History The idea that lying produces physical side-effects has long been claimed. In West Africa persons suspected of a crime were made to pass a bird’s egg to one another.[citation needed] If a person broke the egg, then he or she was considered guilty, based on the idea that their nervousness was to blame
They’re not really very accurate and you can get around them. It’s called glavanic skin response. A lie detector works by measuring changes in skin conductance on the basis of sweating. It uses the fact that when you lie, your skin usually goes up in its conductivity because you sweat, and you sweat because you’re nervous. This is also linked to blushing. There’s another group of researchers who in the past few years have been looking at another way to tell if you’re lying, which is studying closely the blood flow across the face. Although this is probably still undergoing tests, they found that when people tell a lie, the blood flow around the eyes specifically changes and increases blood flow. Even if your eyes aren’t sensitive enough to pick it up, a clever camera can. So you can look at the heat or thermal changes in someone’s face and tell whether they’re trying to hide something. This would be useful, say, at the airport. If someone’s checking in and says no when asked if there’s
http://science.howstuffworks.com/questio… This link explains everything. Just have a quick read through and you’ll be good. Basically a lie detector or polygraph measures the person’s breathing rate, pulse, blood pressure and perspiration, and sometimes record any sudden twitchy movements in the arms and legs. The person taking the test is hooked up to the polygraph machine and asked simple questions in order to establish that the machine is working properly etc, then the real questions are asked. The results are studied by professionals at the end. If there is any significant changes in the person e.g. increased heart rate and blood pressure, increased sweating, twitchiness etc then it will be clear the person isn’t being honest. Just read through you’ll be fine.
