Detecting Lies

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Detecting another's lie is often difficult. Blushing doesn't always occur with deception.  So, criminal investigators sometimes turn to technology to help detect lies.

The lie detector often called a polygraph, works on the assumption that telling a lie causes emotional stress.  This alters the pulse and breathing rate, the amount of perspiration, and muscle tension.  All these physical changes can be detected by sensitive instruments and immediately graphed.  For example, the skin's ability to conduct electricity varies with the amount of perspiration produced.  If someone is ‘sweating the question', the machine will pick it up.

The graphs obtained when carefully selected questions are answered, are compared with those obtained in response to innocent questions, like "Is your name Fred Jones?"  The theory is that if a person lies, the machine will detect the changes caused by the stress of lying, and record them graphically.

But the polygraph is by no means foolproof, since some people are so nervous, they appear to lie, even when telling the truth.  Others can so control their emotions that they are able to lie with little change in polygraph traces.  In order to beat a lie detector they try various techniques to make their responses to the control questions appear as similar as possible to their responses to the real questions.

So next time you're tempted, the best advice is to stay stress-free by sticking to the truth.