Damage to brain may concentrate mind on lie detection

People who lose their ability to understand words because of brain damage apparently compensate for the loss by becoming significantly better at detecting liars.

Damage caused by strokes or tumours can disrupt the circuitry which allows the meanings of words to be understood, a condition known as aphasia. Research published today in the journal Nature suggests, however, that aphasics are better able to recognise subtle facial expressions indicating the telling of an untruth.

Tests have shown that most subjects have no better than a 5050 chance of detecting a lie from a person's demeanour, says the report, whose lead author was Dr Nancy Etcoff of Massachusetts General Hospital East. "We found that aphasics were significantly better at detecting lies about emotion than people with no language impairment, suggesting that loss of language skills may be associated with a superior ability to detect the truth."

The subjects were shown videos in which volunteers described their emotional response to distressing or pleasant scenes. They told the truth on some occasions and lied on others.

These videos were in turn shown to 10 aphasics with damage to the left half of their brains, to 10 people with damage to the right half, to 10 controls and to a group of 48 students. The aphasics got it right 73 per cent of the time on average. They were also better at identifying lies if only facial clues were available.