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What is a lie detector test? All you need to know

A lie detector test is a test that is used to try to establish whether a person is telling the truth or whether they are lying. Some people call it a polygraph test. The test is based on the general principle that certain physiological changes occur in a person’s body when that person is lying.

  • The Principle Behind the Idea

    The whole idea behind using these detectors is that the rate or speed at which certain physiological functions occur when a person is lying is different from the rate at which they occur when the person is not lying. These physiological functions or processes are the respiration rate, the conductivity of the skin, blood pressure and heartbeat or pulse rate. The assumption is that if a person is lying their rate deviates  from the normal.

  • How are the Tests Carried Out?

    The tests are used in many countries which include the USA, Russia, South Africa, Japan and many others. The way it’s done in the different countries follows the same general guidelines and the technology used is basically similar. The first thing done is that the subject being tested undergoes a pre-test interview lasting approximately 20 to 40minutes. The aim is to help prime the subject on the questions to be asked and is also supposed to help the subject to relax. To further help the subject to relax, he is given a short practice test on the general subject matter. The interviewer explains to the subject how the actual test is going to be carried out. Then, the subject is hooked up to the machine. Respiration rate is measured by Pneumographs wrapped around the chest. Pulse rate is measured using a blood pressure cuff. Skin conductivity levels are measured via electrodes attached to the fingertips. If the answers to actual questions produce greater physiological changes than responses to the actual questions, then the subject is presumed to be lying and vice versa. 
  • What are They Used For?

    Different countries make different uses of these polygraph tests. In the United States, law officials like the FBI as well as CIA use the tests as an interrogation option to help them establish whether a suspect is telling the truth or lying. When some governments are screening candidates for high office in departments that handle sensitive information they make use of the detector test to try and make sure that candidates are giving accurate and truthful information about their backgrounds.

  • Are they Accurate?

    Now there is a question that has stirred controversy since the time that the lie detector test itself was invented. There are both supporters and opponents when the question of its effectiveness is raised. Assessments done by government forensic agencies and other scientists tend to condemn polygraph tests as being not accurate. Others are of the idea that sophisticated subjects can actually ‘fool the stupid machines’ to produce results that they themselves want. Others correctly point out that scientifically speaking, it is not possible to get physiological responses associated with not telling the truth and therefore they point out that it is foolish to regard it as being of any use in distinguishing between liars and truth -tellers.

  • How Reliable? 

According to the American psychological Association, a lot of psychologists dismiss the very notion that polygraph tests can be considered a reliable source in detecting lies. An interesting observation was made in 2002 by the National Research Council when they confirmed that polygraph tests seem to produce more accurate results when the subjects undergoing the tests have no idea of the purpose or the reason for the test. 

Other opponents of the lie detector test direct their attacks on the very principle on which it is based .They point out that the physiological responses that are attributed to lying could be due to something else, like nervousness caused by the atmosphere in the interview room. They also point out that it is unreasonable to expect a perfectly innocent subject who is being mistakenly accused of committing an offence to remain perfectly calm when being strapped up to the machine and bombarded with all those questions. The subject will obviously feel jittery and this will trigger those physiological responses leading to completely wrong conclusions.

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