How does the polygraph work?
Surely you have seen the famous lie detectors or polygraphs on more than one occasion in movies, and you have wondered how the polygraph works . It is an instrument with which you can check if a person is telling the truth or not. Nowadays, these devices are widely used in companies, as part of the selection of personnel.
In this short article, we will talk to you about how this device actually works and how it is used.
What is a polygraph and how does it work?
The first thing to know is that the polygraph is not a police instrument, but a medical one. Even though many people believe that it tells you if a person is lying or not, these don’t work that way. The polygraph is responsible for recording the physiological activity of a person . And this information is generated from the individual’s own nervous system.
Knowing this, we have that it is a device that contains an arm with a needle at the tip (in older models, today they are digital). With this, the polygraph is drawing lines on paper according to the physiological responses that the person is having during the interview.
Obviously, with the result of these physiological responses , an expert can come to know if a person is lying or telling the truth. The human body has responses such as fear, doubt, shame, etc. Even if you hide this from other people, the truth is that your body and your physiological responses do not lie.
However, to manipulate and read the results of these devices requires experience and study. Therefore, not everyone is capable of reading and using a polygraph .
A little history about the polygraph
This instrument was born in 1921 and was created by John Larson, and he was in charge of recording changes in blood pressure. From this moment it was that this instrument began to be used to detect lies . Later, this was improved by Leonard Keeler in the 1930s who perfected it creating a much more effective and precise device. Since this not only measures blood pressure, but also the rate of pulse and respiration .
Years later Keeler developed graph paper to implement a new printing mechanism. This made the polygraph results last.
Years passed and more companies became interested in these devices and began to be sold commercially. Even in 1945 John Reid developed a system for recording muscle activity . This was achieved thanks to a special chair that measured the movements of the individual.
For the decade of 1992, Stoelting launches an improved version , which was the first digital polygraph . This, instead of printing on paper, the results were displayed on a computer screen. From here, polygraphs began to be more compact and precise. However, it is still possible to find some traditional needle polygraphs. Even John Larson’s first polygraph can be found at the Smithsonian Institution in the United States.