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The polygraph test popularly known as the Lie detector test is a subject of curiosity and wonder among people. The nearest that most people have come to know this experience is through crime thriller shows or movies and it all seems very mysterious and fascinating. It has always been a subject of scrutiny over how accurate and reliable it is as a source of information. Regardless of how accurate it is, going on the box can shake the nerves of even the strongest person as it is a most intimidating process.

What is Polygraphy?

It is the process which is used for a comprehensive study of various responses, voluntary and involuntary, that the body produces while a person is asked to answer several questions. The observations are particularly dependent on these physiological changes-

  • Respiratory
  • Cardiovascular
  • Peripheral nervous response

The test mainly has three major stages

The Pre-test

During the pre-test, the examiner and the subject have a conversation during which they learn more about each other. It’s like a small ice-breaking exercise. Next, the examiner explains the process of the test to the subject, he shows how the equipment will be attached to his body and for what purpose, and he also answers any questions that the subject might have regarding the testing process. The matter for which the polygraph test is being conducted is then discussed while the subject narrates his or her side of the account of the events and the questions they’ll be asking are agreed upon after discussing. What the subject doesn’t realize is that he is under observation, even during this stage when he’s unattached to the polygraph. The examinee watches the subject closely, keeping him under his scrutiny from the very start, seeing his responses, the pattern of his speaking, note his body language, and tries to learn the most about his behavior as he can. This is the longest part of the test and usually takes an hour or more. It is extremely important as the examinee learns the subject’s behavioral responses by seeing how he processes the questions and react to them and how he actually answers to them.

The Test

This is the stage where the subject will go through the actual test and the polygraph will be attached to his body. There are two rubber tubes filled with air which is tied around the subject’s body. One tube is placed across his chest and another at his waist. This instrument is called a Pneumograph which is used to measure the respiration and movement when the subject breathes. It notes the changes in the air pressure inside the rubber tubes and sends this information to the monitor which is recorded.

After the Pneumograph, GSR (Galvanic skin response) which has small plates is attached to the subject’s fingers and it measures the changes in skin’s reaction. Our fingertips have many sweat glands and hence they’re ideal for attaching the GSR to them to detect perspiration.

The last piece is the Cardiosphymograph which is used to measure the subject’s heart rate and blood pressure. It is inflated with air, which carries the sound of the blood flowing in the veins to transmit it to the monitor.

The examiner observes the monitor throughout the examination process.

After all the equipment have been properly attached, the main part of the test begins. Usually, the examiner asks 10-11 questions, but only a few of them are relevant to the actual interrogation about the crime or issue. The rest of the questions are called control questions. These questions are very generic for eg, ‘Have you ever cheated in your life?’, – the question is very vague and broad and no one can really honestly deny doing that. This is how the examiner gets the idea about how the subject reacts when he’s being deceptive.

The questioning part takes about half an hour and the equipment is removed once it’s complete.

Post Test

The final phase is when the examiner analyses the physiological reaction and decides whether the person has lied. The results once received are provided to the subject immediately. If the test results say that the subject has failed, he is given a chance to explain the results and the deception at which the test result indicates.

It is alright to assume that everyone is nervous and anxious during the lie detection test, but it does not affect the results because the anxiety remains throughout the test and does not cause any significant fluctuations in the readings. However, the chances of human error are also there if the examiner misinterprets the subject’s responses but it is rare. These errors become more possible If the pre-test is not carried out properly which causes him to misread the data post test.