How does a lie detector or polygraph?

You hear about lie detectors in films, TV series, and in the course of police investigations, but sometimes even in our country the person applying for work in one way or another “serious” company, must pass a polygraph test. The purpose of a polygraph – aka a lie detector – is to understand whether the person speaks the truth or not answering certain questions. In Russia, the use of a polygraph is legal since 1975, but the official use of the instrument received in the 90-ies of the last century. But how reasonable the use of such technology, for the disclosure of murders, rapes, robberies, military interrogations?

How does a lie detector?

When a person passes a polygraph test, to it are attached four to six sensors. The polygraph is a machine in which the multiple (“Poly”) signals from sensors are recorded in the form of graphs (“Graph”) on the screen or on paper, depending on how you value the truth. The sensors usually record variables such as breathing, heart rate and blood pressure. Cuff blood pressure measures as blood pressure and heart rate.

Two tubes, one around the subject’s chest and a second around the abdomen measure breathing rate (air pressure in the tubes changes as the breathing). The electrodes, called galvanometers, which are connected to the fingertips measure perspiration. Let me remind you that sweat is a good conductor of electric current because it consists of water and dissolved mineral salts, as well as some products of metabolism. As the sweat level is increased, the electric current flows through the electrodes more freely. The polygraph records these physiological responses during interrogation. Sometimes polygraph records such things as the movement of arms and legs.

How is your interrogation on a polygraph?

Check on the lie detector starts with three or four simple questions to set the norm signal for each person. Then ask the real questions, check the polygraph, and all signals of the human body are recorded. The examiner develops an individual test system, containing from 100 to 200 questions. About 35-50 questions are intended to find out the answer to one question. Both during and after the test, the polygraph examiner can look at the charts and see how to change the indicators on any of the questions. It is believed that a significant change (eg, increased heartbeat, increased blood pressure, increased perspiration) indicates that the person is lying.

Accurate answers gives a polygraph?

In fact, the lie detectors in a primitive form existed for long time. Ancient Indians determined whether the person speaks the truth, instructing him to spit out a mouth full of rice on the sheet. The person who is telling the truth — spit you out without all the grains; and the one who will lie, rice will get stuck in your mouth. This process presumably depended on the dryness of the mouth, which is a physiological factor associated with lying.

The Creator of the polygraph, the cardiologist sir James Mackenzie invented this miracle in 1906 and used it purely for medical research. In 1921, a student of Harvard University William M. Marston — American psychologist and author of the comic book “Wonder woman”, invented the modern polygraph. And after 86 years, the lie detector is digitized. This increased its accuracy and efficiency in the definition of a lie. Most experts generally hold the view that the test of the digital polygraph gives 97% accuracy. However, any results with a confidence of 99.9% is not – it is just a publicity stunt of some polygraph examiners who want to get order at any cost. Real, a fair percentage of the result is between 85% and 97%.

When a well-trained examiner uses a polygraph, it can detect lying with high accuracy. However, as the interpretation of expert subjective and different people react differently to lying, a polygraph test is not perfect and the lie detector can be fooled. Therefore, the discussion about the need for the use of the polygraph does not cease to this day, and its parties take diametrically opposed positions.

It turns out, the world was split into supporters and opponents of the polygraph.scientists agree that polygraphs are able to measure bodily changes, but disagree about whether polygraphs and other lie detectors to accurately distinguish truth from falsehood. Opponents of this hypothesis argue that the polygraph test detects bodily changes associated with anxiety, but because none of them is a reliable way to recognize a lie. Besides, polygraph tests take a variety of forms and are used by different testers in different ways.

Among the factors that affect the results of polygraph tests are the following:

  • Extreme emotional tension or nervousness
  • Anger
  • Concern over neglect of duty or responsibility that made possible the Commission of a crime
  • Physical discomfort during the test
  • Excessive number of test questions
  • The use of drugs
  • Bad wording of the question
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