How to spot a fibber

Liars give the game away by taking longer to answer questions than people who are telling the truth, new research reveals.

Scientists have discovered that being dishonest requires significantly more thought than telling the truth - and fibbers therefore need longer to concoct their reply than those answering honestly.

Their findings reveal that conventional lie-detectors, which pick up medical readings such as heart rate and blood pressure, focus on the wrong signals and are far more complex than necessary.

Instead, they say the vast majority of liars can be caught out using a simple computer test measuring how long they take to respond to questions. Dr Aiden Gregg of the University of Southampton's Department of Psychology, who led the study, said: "Our studies clearly show that it takes people longer to lie than to tell the truth. It seems the process of lying is more confusing and complicated, slowing them down.

"Assuming that truth-tellers are striving to be truthful, and that liars are striving to lie, the task can tell the difference between the two groups nearly 90 per cent of the time."

Businesses and intelligence agencies across the world have invested millions in the quest to find a foolproof way of spotting lies. Devices include a scanner that picks up brainwaves, a machine to detect facial heat and technology identifying changes in the pitch and tone of people's voices.

Conventional lie-detector machines, known as a polygraphs, are used by detectives in the US but are considered too inaccurate in Britain.

In three studies, about 50 volunteers were presented with a list of statements about themselves and the world, some of which were true, and some of which were false. They were asked to repeatedly confirm or deny the statements by pressing one or two keys on a computer as quickly and accurately as they could. Some of the group were told to lie about some of the questions.

The results revealed that those who had to lie took significantly longer to complete the task than truth-tellers. The research team claims the system has a success rate of more than 90 per cent.

The team, whose findings will be presented at the British Psychological Society's conference today, believe the system could become a valuable tool for British police. Suspects would be asked to respond to simple statements such as the ones in the study, allowing detectives to work out their response times when lying or telling the truth, before being asked crucial questions about their involvement in the crime.

Dr Gregg, who is working on computer software to market to businesses and intelligence agencies, added: "Our system would not be used to provide actual evidence for or against someone, but could provide a very useful insight."