I remember once when I was looking for a job there was an interview in one serious and famous company. The casting for the working place was divided into several stages. I successfully had passed two of them already and was waiting for the third one. To my surprise, next check was done with the help of a lie detector. Wow! I did not know almost anything about that and understood that my answers should be sincere and true.

This recollection inspired me to learn how the machine works. I became also curious when it was invented and who was that clever guy who had done that.

Lie detector was invented quite long time ago, in 1921 in California. The person who was smart enough to bring into life such a machine was a police officer John Larson. He based his invention on results of a pioneer in this field William Moulton Marston, having created a test on the ground of the systolic blood pressure. He was first to claim that when a person does not say the truth, his blood pressure would change.

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Lie detector, the other name is polygraph, is a device which records biological reactions and states (such as pulse, respiration, blood pressure and conductivity of skin) meanwhile a person answers some essential questions. If there some «response conflict» detected, it may be a signal that a person is lying.

WHAT IS THE PROCESS STAGES?

Testing process usually starts with a pre-test questions for the person to understand what everything is about and be sure that the questions are clear. There are used only yes-or-no questions during all the procedure.

It goes without saying that the tester explains what polygraph is, how it works and tries to persuade a person that any lie will be visible due to the machine. After that the interrogator puts different types of questions:

• irrelevant or neutral (e.g. Do you live in the USA?)
• diagnostic or important (e.g. Have you taken this camera?)
• relevant or control (e.g. Have you ever taken anything that did not belong to you?)

Why do they reveal the questions that will be asked at the main part? Because it is essential that the person think about the topic and is ready to understand all the questions the way they should be understood.

After the pre-test there is a stimulating test aiming at making sure that the person is completely believes that the technology is able to detect any lie. This stage is done with playing cards in most cases. After remembering one of them, the interrogator «guesses» what the card was. Thus, the polygraph records physiological reactions on saying the truth.

Finally, the main stage is coming up. Here different types of questions are asked like in pre-test part.
For example,
-- Do you live in the USA? - Yes.
-- Have you ever taken what did not belong to you? - No.
-- Have you taken this camera? - No.
-- Is your name Nick? - Yes.
-- Until 2010 did you do anything illegal? - No.
-- Have you taken the camera? - No.
-- Were you born in April? - Yes.
-- Have you ever lied to avoid problems? - No.
-- Are you connected somehow to the stealing of the camera? - No.

It is visible, that control questions are repeated very often to avoid accidental differences in body reactions.

The fourth stage includes test interpretation.

Obvious, that the role of interrogator in this process is the most important one, because he has to formulate control questions in such a way that they should provoke the strongest reactions in unguilty people. On the other hand, in people who are suspected in a crime the strongest reaction must be for diagnostic questions. So almost everything depends on the interrogator’s skills to hold such interviews.

However, it does not matter how genious this technology is, scientific community considers it inadmissible. The courts cannot accept its results as proof of guilt. But despite this, a lot of private organizations use it when they look for employees, as well as police departments take advantage of it doing investigations.

The world of science does not accept this technology because it claims that there is nothing to do with science, it is all about interrogation. The sign of sweat does not necessarily mean that the person is hiding something. Then, it becomes interesting is it possible to cheat the polygraph?

At first, visit the AntyPolygraph website presenting facts againts efficiency of a lie detector. For instance, they made a research suggesting that black people who are actually innocent are more likely to fail the test than innocent white people. They assert that the polygraph is trickey rather than a professional device. One of the proofs is that one of the most famous killers in the USA passed the test. Medicals say say that people with psychological problems can mix the reactions or do not feel any guilt about actions done.

Watch this video from the NSA.

And this one might be of interest as well.

Well, summing up, the idea of polygraph is very interesting in terms of checking how much people are sincere, but at the same time it has flaws making this device less reliable.
And what is your opinion?

Sources: 1, 2, 3, 4