Medical experts in the USA and Britain say that it is quite possible for a suspected person to beat the lie detector. The trick is to make the responses to the control questions appear as similar as possible to the responses to the real questions. For an answer to be classified as ‘deceptive’, it must register much more strongly than the control answers.
Dr David Thoreson Lykken, professor of psychology and psychiatry at the University of Minnesota Medical School, writes in his book A Tremor in the Blood that the interviewee could identify the control questions during the pre-test interview. He could then do something to increase his response to control questions during the test – something different each time so as not to arouse suspicion.
‘After the first control question, I might suspend breathing for a few seconds, then inhale deeply and sigh. While the second control is being asked, I might bite my tongue hard, breathing rapidly through my nose. During the third control question, I might press my right forearm against the arm of the chair or tighten the gluteus muscles on which I sit. A thumbtack in one’s sock can be used covertly to produce a good reaction on the polygraph.’
Dr Archibald Levey, of Britain’s Medical Research Council, who wrote a report on lie detectors for the British Government in 1988, says that meditation techniques can be used to achieve the opposite effect – by lowering the responses to all questions.
The interviewee could think himself into a relaxed state, concentrating on a different subject or imagining himself to be somewhere else.
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