Give him the lie
The 'lie detector', or polygraph, makes marks on a strip of moving paper as the suspect talks. It works on the theory that lying causes stress, triggering changes in bodily functions that can be recorded, explains Prakash Chandra.india Updated: Jan 15, 2007 00:09 IST
When did you last wonder if somebody was lying or telling the truth? After all, a clear conscience could also be due to a bad memory. Pinocchio had an inbuilt lie-detector system, but criminal investigators have to rely on methods like hypnosis, fingerprint testing, handwriting evidence, and DNA analysis to extract information from suspects. Psychoanalytical tests like the ‘lie detector’ or polygraph test, brain mapping, and narcoanalysis are more recent techniques.
The ‘lie detector’, or polygraph, makes marks on a strip of moving paper as the suspect talks. It works on the theory that lying causes stress, triggering changes in bodily functions that can be recorded. The ancient Chinese knew this and would first ask a suspect an easy question like, say, ‘Is it raining?’ They would then tell him to put a handful of rice, whose grains they’d counted, into his mouth and spit it out before asking a tough one like, say, ‘Did you steal?’ When he spits out the rice now, if more grains come out, they’d know he’s lying as the stress makes his mouth drier, making fewer grains stick in it. The polygraph, of course, doesn’t use rice; instead, sensors record breathing rate, blood pressure, perspiration, and limb movements.
But this is controversial as it’s no better than flipping a coin to determine who’s lying and who isn’t. A good alternative is brain ‘fingerprinting’ that matches information in the brain with information from the crime scene. An innocent suspect’s brain wouldn’t store certain information, unlike a perpetrator’s brain. In narcoanalysis, a person is given drugs — ‘truth serums’ — that suppress his reasoning power without affecting memory and speech. In this ‘twilight state’, he can be made to tell the truth. For a person lies by using his imagination, and once this is neutralised, his answers would be restricted only to facts he is already aware of. Sodium Pentothal, for instance, could make the suspect so garrulous and ‘confessional’ that he ‘sings like a bird’.
Medical detection of false testimony holds even more promise, as it’s easy to measure the presumed fear of detection better. Fear dwells in a brain region called amygdala, and its telltale activation can be recorded in an MRI scan. New research also focuses on the use of infrared cameras to detect temperature changes caused by variations in facial blood flow; lasers to spot muscular, circulatory, and other bodily changes; voice stress analysis, and brainwave monitoring. Some day, high-tech lie detectors may be impossible to fool, but so far the only guarantee is that they will stir up as much controversy as the original polygraph.
First Published: Jan 15, 2007 00:09 IST