20-02-2011, 05:59 PM
The POLYGRAPH and lie detection
The polygraph instrument (generally known as the lie detector) measures as well as records the various physiological signals such as BP, pulse, respiration, skin conductivity, body temperature, breathing rhythms,galvanic skin response or GSR(skin resistance) etc while the subject is asked the questions based on the crime. It is presumed that the false answers will produce measurements that are distinctive from the normal. The sympathetic nervous system causes the physiological changes during the questioning and this is measured by the polygraph.
A variety of physiological changes occur in the subject when he lies. The heart beats faster,breathing rate increases, and the BP shoots. The results are plotted on the graph sheet and the medical examiner can distinguish it from the normal.
The examiner first establishes a baseline for these physiological parameters. The deviation from these baseline is identified as a indicator of lying.
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