How Does A Polygraph Device Operate

How Does A Polygraph Device Operate?

Have you ever heard about a polygraph device? Do you know how the polygraph works?  Do you have any information about how to perform a polygraph test? These are the questions which the following article answers and explains. You will be more familiar with the way polygraph monitors biotic signs, the test process and the legality of the exam. Moreover, you will study about lie detection and the reasons people lie.

As you know, polygraph or lie detector is a machine that detects lie with the help of the person’s psychological and vital signals.

Why people Lie

The act of deceiving has many different types and lying is just one of them. indeed, lying is a form of communication and assertion that involves the deceiver and the deceived. At age three or four, we all start lying. At this stage of brain development, we understand that we have a magical tool named language. Gradually, we learn to use it in order to play with reality and impact the consequence of what’s happening. There are several reasons people lie. The following are some of the main reasons why people lie.

  • Protection – This can occur in two forms of protection for others and protection for oneself. For example, being threatened or reducing the damage, harm, or consequences.
  • Personal benefit – This includes loss of job, loss of reputation, personal humiliation, fear of judgment, loss of respect, loss of love, desire to keep the truth, criminal conviction, jail time, getting the attention of other people and etc.
  • Personal grudge – Some people lie because they feel harmed by that person and they held a grudge against them.

For whatever the reason, the fear of revealing the truth causes physiological changes the polygraph device records and the examiner analyzes.

Detecting lie

Lie detection is an important subject in psychology and law. It is also a principal field of applied psychology. Polygraph theory describes that the majority of the people who are lying, feel anxiety, fear and nervousness.

For this purpose, psychologists and practitioners invented different kinds of tools for analyzing behavior and speech as well as physiological responses to recording brain activity.

Frequently, telling lie is a defense mechanism in order to prevent problems from the law or rules and authorities. Polygraph or lie detector is a machine that observes and checks a suspect’s physiological reactions. As the polygraph etymology describes its meaning, it does not detect lies. It can just detect kinds of seductive behavior.

What is Polygraph >

Polygraph device and tools

The basis of using polygraph goes back to a hypothesis. Based on this hypothesis, the administer who works with the so-called lie-detector, can construe the conscious deception from certain involuntary physiological responses. This is exactly the way doctors correctly diagnose different diseases. Because scientists and psychologists proved that lies make emotional disturbances. In other words, this assumption describes when a person feels apprehension, fear, or emotional excitement, his or her respiration rate, blood pressure, and galvanic skin resistance strongly increase.

Actually, the device is a composition of various recording machine usually used in the medical and scientific community. The device simultaneously recorded chosen physiological activities while an examiner questions the examinee under controlled conditions. As a result, when a normal individual makes conscious mental effort to deceive someone, he shows physiological changes. Accordingly, the polygraph machine detects them. The autonomic nervous system that regulates the body’s internal environment drives these changes. One part of the autonomic nervous system is the parasympathetic nervous system. It is related to relaxed situations and performs functions such as digestion and maintenance of body temperature. In endeavoring to conceal the truth, no matter how much a person tries to prevent physiological changes, it is useless.

Some investigators are under the misinterpretation that if an examinee answers the questions without a feeling of guilt for committing the crime or moral reasons due to the upbringing and social background, this person is not a mendacious. This misinterpretation leads some people to believe that these suspects can deceive the examiner as well as polygraph device because of their background or deviant personality.

The aim of a polygraph test is to find whether somebody is telling the truth or lying while answering certain questions.

lie detector device polygraph device

Polygraph Device Components

What does the Lie Detector Test measure? How does a lie detector know you lying? These questions underscore the importance of the study and development of polygraph device. The lie detector test analyzes the response to the test stimulus.

The device is connected to various medical parts of the body.  To taking a polygraph test, four to six sensors will be attached to the person, often on the chest and fingers. The blood pressure cuff is wrapped on the person’s arm which records pulse and blood pressure. The rubber tubes place over chest and abdomen records respiration rate. In addition, two metal plates are attached to fingers in order to record perspiration or sweating. Also, a laptop is connected to polygraph device.

These sensors analyze and record the following things during the test:

  • The arm and leg movement
  • Muscular activity
  • Breathing rate
  • Number of beats/pulses
  • Blood pressure
  • Perspiration
  • Nervous excitement
  • And other psychological signals of the individual

Lying is followed by a rise in heart rate and blood pressure that is recorded by a cardiograph. Furthermore, rise in breathing rate is measured by a pneumograph or spirograph and perspiration (sweat) is evaluated and recorded by variation in electrical resistance of the person’s skin. When the person sweats, the electrolytes in perspiration or sweat are increased.


As the test is starting, the questioner asks simple questions like “Are you 43 years old?” and so on. Then, the basic questions will be asked and the recording all the person’s signals on the moving paper will be starting. The signals recorded on the moving paper shows if the signs altered remarkably in each of the questions. Generally, the remarkable changes demonstrated lying.

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