How is a lie detector test done?

A lie detector test is done using a polygraph machine. It was invented by John Augustus Larson in the early 19th Century. It’s called a “poly” graph machine because it records various physiological indices like blood pressure, the pulse, respiration pattern, and skin conductivity of a person.

The person who undergoes a polygraph test, is asked a series of questions and any change in his blood pressure, breathing pattern, pulse rate, or skin conductivity determines whether he is lying or not. A polygraph machine is being used since years for questioning probable suspects of criminal cases.

Polygraph tests are also done on applicants for jobs that are of top secrecy like the FBI or CIA where the credibility and honesty of the applicant matters a lot. People conduct polygraph tests for determining infidelity as well. So, we can conclude that a lie detector test is used for legal, government, professional and personal purpose.

The polygraph test when conducted by a well-trained person can give maximum accurate results. However, it’s a scientific procedure and not magic. This is why there are ways to manipulate this test and people can get away even if they lie. It all depends on confident you are when you take the test and how you control your calm while responding to the questions.

Generally, when the subject who is undergoing the test is being asked questions, his responses are recorded on a carbon paper which is fixed on a rolling drum. This is what the “graph” in a polygraph represents. However, the person can always cheat this test even if he’s lying.

The easiest way is to have control over yourself when you lie and not get worried at all. But that can be done only by a few people who have expertise in lying. Normal people tend to sweat and worry when they are asked things to which they cannot respond honestly. The other way a polygraph test can be cheated is by understanding the procedure carefully and manipulating it.

The test starts with a few simple questions to the subject which may not be directly related to the case or actually topic of the questioning. These initial questions are called control questions. The person will obviously answer them without any worries and the physiological indices under measure will come up with a reference graph which is then used to check if the person is lying or not in the following questions.

A person can be nervous and try to increase his heart beat rate and breathing rate during these control questions to maximum so that later on when the actual questions are asked, these rates won’t be higher than the reference rates even if the person is lying and is nervous. This will prove that the person is speaking truth even when he is lying. This is one among the worst draw backs of  a polygraph test.

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