Polygraphy test of Sanjay Roy, accused in Kolkata rape and murder case, is to be conducted today. After getting permission from the court, now CBI will do this test and through lie detector machine it will be possible to know how much lie and how much truth the last accused is telling. In such a situation, the question is, what is this polygraphy test and how does its machine find out whether a person is lying or not? Also let us know what questions keep arising regarding the machine. So let us know every single thing related to this machine…
What is polygraph test?
Many times, to get the accused to reveal the truth, the police conducts a polygraph test, in which an attempt is made to detect lies through a lie detector machine. In this, through the changes occurring in the body during the answer of the accused, it is ascertained whether the accused is answering the question correctly or not. In this test, the physical activities of the accused are read carefully and according to their reaction, it is decided whether the answer is true or false.
How does this machine work?
This is a machine, which has many parts. In this, some units are attached to the body of the accused. For example, machine units are placed on fingers, head, mouth and when the accused answers, data is received from these units, which goes to a main machine and detects the lie or truth. The units connected to the body include pneumograph, cardiovascular recorder and galvanometer. Also, pulse cuffs are tied on the hands and Lombroso gloves are worn on the fingers. Along with this, blood pressure, pulse rate etc. are also monitored through the machine.
Pulse rate and breathing etc. are monitored through a pneumograph in a device worn on the body. During the answer, lie and truth are judged through breathing. It has a tube, which is tied around the chest. Heart beat and blood pressure are monitored with a cardiovascular recorder, because when lying, there are abnormal changes in it, through which the truth can be detected. Also, the electrical conductivity of the person’s skin is checked through a galvanometer. Then this data is collected through a recording device.
How is the truth known?
First, normal questions are asked to the accused, which are not related to the case. Then most of the questions are asked in yes or no format and its experts find out the truth from the data of that machine. In this, results are obtained based on the data of pulse rate, blood pressure, breathing, skin changes and physical senses. A different signal comes out from the brain of the person who lies. When a person gives a false answer to a question, a P300 (P3) signal comes out from his brain. In such a situation his heart rate and blood pressure increases.
Can anyone get the test done?
To get polygraph test done, first permission has to be taken from the court and considering the need of polygraph test in the case, the court gives permission to get this test done.
Is the result always accurate?
But, the thing to keep in mind is that polygraph test is not always accurate. The test can sometimes show that a person is lying when they are actually telling the truth. Actually, the machine finds out the truth based on the reaction of the body, but sometimes the result can be wrong due to the mental condition of the accused. Simply put, a polygraph test does not detect lies, it detects signs of emotion.
What is the difference between narco and polygraph?
In polygraph test, truth or lie is judged through machines on the basis of data like pulse rate, breathing, blood pressure, sweat, skin changes etc. In this the accused remains in his full senses, but the narco test is different. Truth and lie are also detected through narco test, but in this the person is given an injection of a medicine called sodium pentothal. Then he becomes half unconscious and is unable to lie. In such a situation, truth or lie is ascertained from the accused.