The polygraph, commonly known as a lie detector , has become part of our society since it became known in the late 1930s and was invented by John Augustus Anderson and Leonarde Keeler.

When this machine began to be used, many experts in the field asked themselves the same questions that, even in today’s society, are the order of the day: is the polygraph an effective procedure for all people who undergo or have undergone it, is its detection system easy to circumvent, and to what extent should it be considered an infallible method for detecting lies?

These are reasonable doubts, bearing in mind that the machine is capable of calling its victims into question and creating situations of ambiguity if it does not know how to respond to them. Next we will see how the polygraph works and how effective it is .

The origin of the polygraph

The Italian Cesare Lombroso (a prominent anthropologist of the last century), studied the relationship between the changes that take place in the cardiovascular system and the body’s reaction to lies. He focused his research on two aspects of the human being: heart rate and blood pressure . From this study, through new developments and progress in the technique of human behavior, they contributed to the creation of the polygraph, an invention of John Augustus Larson and Leonarde Keeler.

Since then, the polygraph has become an indispensable tool for some sectors, such as justice, police and army , mainly, in order to help detect people’s lies and/or deceptions.

How do you use it?

The operation of the device itself does not require great skill on the part of the expert handling it; he will “only” pay attention to the interviewee and the results coming out of the polygraph test.

First, the person with whom the polygraph is to be used participates in a conversation (previous interview to the polygraph test) with an expert interviewer by means of an analysis of the stimulation, better known as the Stim Test , with the aim of subjecting her/him to a series of lies and thus assess whether his/her body responds to neuro-linguistic changes.

Once this interview is concluded, the polygraph test enters the scene, in which the person is connected to a series of sensors that analyse his physiological reaction , and this is revealed on a paper printed by the same machine. On that paper appear the records of the physiological activity that the individual has had while each question was asked.

How does the lie detector work?

What the sensors placed on the skin measure is the electrical conductivity of the skin . These measurements are made in real time, and tell us about the way the pores of the skin open or close to let in sweat, the substance that makes electricity circulate. Other variables taken into account have to do with the heartbeat.

But the polygraph is designed to detect physiological changes in the person’s body, not to detect a lie as such. That is, the device is not trained to know what a lie is by definition , but rather, it shows the body changes that the person undergoes during the course of the polygraph test, without telling us why those changes occur. It is a way of isolating data and, from them, trying to deduce what the logic is that governs the person’s physiological activity and, from that, trying to find out whether he is lying or not.

The dilemma that arises from the reliability of the machine in question is in constant debate, given the infinite variables that human beings present in any type of situation. Thus, it is very complicated to scientifically assess whether a person is lying or not , because that depends, among other things, on whether has the ability to lie or whether he or she simply gets nervous by even telling the truth. The context in which the polygraph is applied is not emotionally neutral, and the subject who submits to the machine knows that a minor change in his body can cause him many problems in the future.

These are vitally important issues that should not go unnoticed by an expert if a fair test result is to be given with complete certainty. The polygraph tells us if a person is physiologically more or less activated (to a certain extent), but of course, technically it is far from being a lie detector.

Legal application of this machine

Its use, above all, is given in some government agencies of the United States of America (CIA or NSA to cite some examples) in order to find out if the person is lying or not. Far from the American continent, its use in European countries is carried out for the allocation of certain jobs in private companies and in security sector agencies.

Thus, the effectiveness of the polygraph in legal bodies is approved and legitimated, above all, in the United States and the countries under its influence , since they consider it to be fundamental evidence in a hypothetical judicial case. The same does not happen in the rest of the continents, since the doubts that have arisen over the years since its implementation in 1938, question the validity of its results.

However, the countries that use the lie detector approve of its use and the results it provides. It is considered as a determining test in a hypothetical case of submission of a person, so it could become an essential factor for the resolution of doubts in a judicial process .

How to Pass the Polygraph Test

Some tips for successfully passing a polygraph test:

1. Understand the operation of the machine

If you’ve made it this far, you should have met this requirement by now. Knowing what one of these tests is is a good way to feel less vulnerable.

2. Sleep well the day before

Arriving at a lie detector test having rested enough makes us more confident . The objective is that the polygraph does not point out supposed lies simply because we are unsure.

3. Tell the technicians about the medicines you take

If you are taking any drugs, it is important to know, as their effects could interfere with the test .

4. Take a deep breath during the test

When you have passed the stage where you are asked the relevant questions, make sure your blood is well oxygenated . To achieve this it is good that you have practiced before, so that you don’t think you are improvising.

5. Remains in a calm state after the interview

It’s possible that once the test is over, the technician will tell you that he knows you lied about something. This is usually a strategy to see how you react to hearing that.