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How to detect lies

Police generally uses lie detector, also known as polygraph, during interrogation.

The instrument works by recording our physiological functions such as blood pressure, heartbeat, respiration and perspiration. A pnuemograph tube is fastened around the subject’s chest and a blood- pressure – pulse cuff is strapped around the arm. Psycho galvanic skin reflex and flow of current between different parts of the body are also measured.

Sensitive electrodes are used to pick up the impulses that are recorded on a moving graph paper. The parameters are recorded when a suspect answers questions put to him by an operator. The data is then used as a basis for deciding whether the person is lying or not.

When a person lies, the graph deviates from the normal shape in one or more of the body functions. Such changes occur due to our emotional response to telling a lie.

Most of the questions asked are interrelated; some are included to improve the test’s accuracy. The questions are usually answered in ‘yes’ or ‘ no’ pattern only.

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