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How Do Lie Detector Tests Work?

July 15, 2017 lie detector 0

Subjecting a person to a lie detector test is one way to check his integrity and credibility regarding a specific situation. Polygraph machines are often used in such tests. But do you know how the actual mechanism of lie detector tests work? How can it truly check if a person is lying or not? Read on and find out more about how lie detector tests work.

The Polygraph Machine and What It Truly Detects

A polygraph is a machine used in lie detection tests. But have you ever reckoned if a polygraph senses your lies and alerts the examiner on such circumstances?

In reality, a polygraph machine is designed not to read a person’s mind and tell that he’s fibbing. Polygraphs actually determine changes in a person’s bodily responses in relation to fibbing.

Polygraphs detect body response changes and record them as line graphs on a continuous sheet of paper. Most modern polygraphs use computer technology, wherein these line graphs are recorded on a computer, alongside the particular questions asked during the time these physical responses were recorded.


Physiological Principles behind Lie Detection

Lie detection tests sit on the principle of physiological responses. The premise is that a person displays significant changes in their physiologic responses when they are lying.

It is easier to tell the truth than to actually lie. The human brain processes truth-telling faster than it can process the formation of lies. When you tell a lie, your brain has to work faster and harder in order for it to look as true as you want it to be.

Because of the brain’s increased work burden during lie formation, the body responds accordingly. Changes in bodily responses include the following:

A racing heartbeat – Lying creates a need for faster body responses, which then call for an increased oxygen circulation in the blood. The heart pumps oxygen-carrying blood faster around the body and towards the brain to compensate for the hard times that a person is trying to form a lie. This explains why heart rate suddenly goes higher during a lying spiel.

Faster breathing patterns – A person breathes in faster if he’s lying than if he’s telling the truth. This is because his brain needs to increase its oxygen levels taken from the environment. He breathes in faster to get adequate amounts of oxygen for his working-double-time brain.

Increased sudden sweating – A lying person experiences increased pressure within his bodily systems. His metabolism suddenly fires up, prompting him to form increased amounts of sweat during the period that he is lying. Sudden sweat found on a person’s face or palms may be indicative that he isn’t telling the truth.

Elevated blood pressure – Accompanying all abovementioned physical changes is an increase in blood pressure. It follows suit – when your heart’s pumping around more blood faster to your brain, pressure inside your blood vessels increases rapidly, leading to a higher blood pressure reading.

Significant changes in speech, tone, bodily gestures, and facial movements can also be observed during a lying spiel. These observations can complement physiologic changes that the polygraph has recorded, and can give a better picture of whether a person is lying or not.

Polygraph Testing Process

The person is led to a room where the polygraph machine and equipment are located. He sits on a special chair which is designed to monitor arm and leg movements. Clips connected to heart rate monitors are placed on his fingers. A blood pressure cuff is also wrapped around his arm.

A stimulation test is then done. Here, the examiner asks the person to lie blatantly. He then records the response and tells the person that the polygraph captured his response as a lie. The stimulation test is done to alert the person that the polygraph is indeed an accurate device, and any chance of him lying can really be caught.

After that, a series of questions will then be asked by the examiner, while he monitors body responses through his own subjective view and through the polygraph. The most typical questioning technique used is called Control Question Test (CQT). The examiner asks control questions that have broad scopes alternating with the real questions.

The test then ends after 2-3 hours. Polygraph results are reviewed, and a person is deemed to have told a lie in areas where physiological changes have spiked up. Physical observation of the person is also included in determining if the person has lied or not.

Final Thoughts

Lie detection tests work by using a polygraph to measure blood pressure, heart rate, and breathing patterns as a person answers questions about his circumstances. Polygraph testing uses the principles of physiological changes mixed with observations in speech, body gestures, and facial expressions, in order to catch if a person is indeed truthful or not.

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