The longest surviving lie

The lie-detector test is like the ancient practice of ‘trial by ordeal’ used to identify a witch.

A file photo of Indrani Mukerjea and her daughter Sheena Bora (Left) (Photo: PTI)

K N BHAT-Feb 17, 2016, 

In criminal cases when police resort to lie-detector tests it should be concluded that the investigation has reached a dead-end and other methods of discovering evidence or eliciting information, including procuring a confession, have failed. Take the recent instances of Peter Mukerjea in the Sheena Bora murder case and Salwinder Singh in connection with the Pathankot attack case — they both underwent the test and Mr Singh reportedly “cleared it”. Shashi Tharoor, in connection with the death of his wife Sunanda Pushkar in January last year is facing the threat of the lie-detector test.

In India the most popular form of lie-detector test is “narco analysis”, where the person is injected with a chemical — sodium pentothal — popularly known as the “truth serum”. The subject enters into a hypnotic trance and answers questions without having conscious control over the replies. Another test is the Brain Electrical Activation Profile (BEAP) test, also known as “P-300 wave test”, where electrical waves emitted from the test subject’s brain are recorded through electrodes attached to the scalp.

The subject is then exposed to external stimuli like sound and visuals relevant to the facts being investigated. The theory behind it appears to be that when exposed to material stimuli, the suspect emits P-300 waves on the basis of which the expert draws inferences.

According to Wikipedia, polygraph is a machine that can measure several physiological indices like blood pressure, pulse, respiration and skin conductivity simultaneously — hence named, polygraph — while the subject answers a series of questions.

The belief underlying the use of polygraph is that deceptive or untruthful answers will produce physiological responses that can be differentiated from those associated with non-deceptive or truthful answers. But, ultimately, the polygraph analysis is like any opinion, say that of a handwriting expert. Mr Singh clearing the lie-detector test means nothing because it is an established fact that the body of a habitual liar does not react differently while giving evasive answers or while uttering outright falsehood. At the same time, many innocent individuals passionate to establish their innocence fail the test due to the fear that the findings might possibly go wron

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