Exposed: the rush of blood to the eyes of a liar

Bare-faced liars could soon be exposed by a new technique for detecting the blushes of expert fibbers whose dishonesty normally goes unchecked.

Scientists have designed a high-definition video camera that can pick up the minute changes in heat given off by a rush of blood to the skin around the eyes when a person lies. Many people who are "good" at lying are usually unable to supress blushing around the eye sockets – a phenomenon exploited by the inventors of the camera, which detects temperature changes of just 0.025C.

The inventors believe the camera could be used at airports and other sensitive facilities for quickly checking whether people are giving honest replies to security questions.

James Levine, a British-born endocrinologist from the Mayo Clinic in Minneapolis, and Ioannis Pavlidis, from Honeywell Laboratories, said the video camera was as good at detecting liars as the polygraph test, the legalised lie-detector used in the United States.

Dr Levine said: "When an individual is exposed to the thermal-imaging camera and is being deceptive, the computer detects the warming around the eyes. This isn't actually the same physiological phenomenon as cheek blushing. It's far more subtle than that and there's nothing you can actually see. The warming around the eyes may be a primal response to deception."

In a study published in the journal Nature, the scientists say the camera is quicker than the polygraph, can be used by non-experts and has the added advantage of not requiring someone to be wired up to the device while being interviewed.

"There is an urgent need to devise technologies that can be used for automated, high-throughput screening to identify individuals intending to perform acts of terrorism," Dr Levine said. "At present, practicalities dictate that we rely on subjective assessment of responses to brief questions such as 'did you pack your own bags?' and 'why are you entering this facility?'."

Traditional lie detectors are impractical for mass screening – they are time-consuming and the results must be interpreted by skilled operators whose judgement is often subjective. The new video technique, however, merely compares the flow of heat to the skin before and after a question is asked and identifies a potential liar when the difference is significant.

Dr Pavlidis and Dr Levine originally used the device to study the tiny heating of facial skin when someone is startled, an involuntary process beyond conscious control. They said: "Were this thermal signature to accompany lying, independently of startling, it could be used for instantaneous lie detection without the subject even being aware of the test."

To test the idea, they recruited 20 volunteers, eight of whom were asked to stab a mannequin and "rob" it of $20. Each person was then videoed with the camera as they were asked: did you steal the $20? The camera correctly identified six of the eight liars – a success rate of 83 per cent – and 90 per cent of the innocent individuals. This proved better than the traditional polygraph test, which had 70 per cent accuracy.

The Pentagon has asked the scientists to describe how their invention could be used for airline security checks.