Modern lie detecting polygraph technique

In ancient times, people used different methods to detect the lies of a person but the era in which we are living adopt modern technique known as “Polygraph”.

Modern lie detecting polygraph techniqueIn some countries accused person were subjected to do water test. The people who sank were considered innocent and those who float were thought guilty.

In India, the accused person mouth was filled with some dry rice. Then they were asked to spit it out. If rice got stuck in their mouth they were thought guilty. Same some witchcraft methods were also implied which was not right for the people.

Some innocent people got hurt and punished for the crimes that they did not commit. So people developed more humane methods. With the passage of time and advancement in science the lie detection techniques have grown better and better.

Polygraph is a modern lie detecting technique. Poly means multiples or many and graph means to write. When a person takes a polygraph test, four to six sensors are attached to him.

A polygraph is a machine in which the multiple (“poly“) signals from the sensors are recorded on a single strip of moving paper (“graph“). The sensors usually record.

The instrument typically used to conduct polygraph tests consists of a physiological recorder that assesses three indicators of autonomic arousal: heart rate/blood pressure, respiration, and skin conductivity.

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Most examiners today use computerized recording systems. Rate and depth of respiration are measured by pneumographs wrapped around a subject’s chest. Cardiovascular activity is assessed by a blood pressure cuff. Skin conductivity (called the galvanic skin or electro dermal response) is measured through electrodes attached to a subject’s fingertips.

The recording instrument and questioning techniques are only used during a part of the polygraph examination. A typical examination includes a pretest phase during which the technique is explained and each test question reviewed. The pretest interview is designed to ensure that subjects understand the questions and to induce a subject’s concern about being deceptive.

Polygraph examinations often include a procedure called a “stimulation test,” which is a demonstration of the instrument’s accuracy in detecting deception. The little elevation in any of these can be considered as a lie. The polygraph technique can be carried out by two methods. First one involves the Controlled Question Technique.

In this, the examiner asks some relevant and control questions. The control questions are designed to control for the effect of the generally threatening nature of relevant questions. Control questions concern misdeeds that are similar to those being investigated, but refer to the subject’s past and are usually broad in scope.

A person who is telling the truth is assumed to fear control questions more than relevant questions. This is because control questions are designed to arouse a subject’s concern about their past truthfulness, while relevant questions ask about a crime they know they did not commit.

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A pattern of greater physiological response to relevant questions than to control questions leads to a diagnosis of “deception.” Greater response to control questions leads to a judgment of non deception. If no difference is found between relevant and control questions, the test result is considered “inconclusive.”

When the polygraph test starts, the examiner asks three or four simple questions to establish the norms for the person’s signals. Then the real questions being tested by the polygraph are asked.

Throughout questioning, all of the person’s signals are recorded on the moving paper. The lie can be detected through stress of lying or heart beat elevation.

Sometimes a polygraph will also record things like arm and leg movement. Second one is Guilty Knowledge test. In this the examiner not only tests the guilt but also the lie of the person.

Examiner asks person a question about the crime. To notice if there is any change in his statement. This will show us if he was present at the scene or related to the crime or not.

More quick and detailed answer can show us he was present. GKTs are not widely employed, but there is great interest in doing so. One limitation of the GKT is that it can be used only when investigators have information that only a guilty subject would know. The interpretation of “no deception” is also a potential limitation, since it may indicate lack of knowledge rather than innocence.

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Polygraph can give false positive results some times which can result in making some innocent person a criminal. Polygraph can be fooled by a trained individual who just need to control his physiological responses. But with trained examiner taking the test there is better chance of getting the result right.

A particular problem is that polygraph technique has not separated placebo-like effects (the subject’s belief in the efficacy of the procedure) from the actual relationship between deception and their physiological responses.

One reason that polygraph tests may appear to be accurate is that subjects who believe that the test works and that they can be detected may confess or will be very anxious when questioned.

If this view is correct, the lie detector might be better called a fear detector. Still ploygraph is better technique then other methods and still new advancements are being made making it more and more reliable.

Muntaha Dastgir
Author: Muntaha Dastgir

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