A heat-sensing camera trained on people's faces was able to detect liars in a study that hints at a way of spotting terrorists at airports.
In six of eight people who lied, the high-resolution thermal imaging camera detected a faint blushing around their eyes that Mayo Clinic researchers said is evidence of deception.
Such facial imaging, they said, could provide a simple and rapid way of scanning people being questioned at airports or border crossings.
But other scientists questioned the significance of the findings, noting that the technique was tested on a small number of people. They also said the experiment fell far short of what is needed to reveal whether thermal imaging can work accurately and quickly in real-life situations.
``What they found is interesting, but it's more than a bit of a stretch for them to say this could be useful for mass screening,'' said Monroe Friedman, a professor of psychology at Eastern Michigan University.
The experiment involved 20 Army recruits. They were randomly assigned to either stab a mannequin and take a $20 bill from its clothing, or not carry out this staged crime.
The recruits were then filmed with the thermal imager as they were subjected to the same questions, with the mannequin-robbers instructed in advance to lie about their theft.
The results appear in Thursday's issue of the journal Nature.
Six of the eight ``robbers'' showed the telltale heat patterns around their eyes. Eleven of the 12 other volunteers were correctly tagged as innocent.
Tests with a polygraph _ popularly known as a lie detector _ yielded similar results. Polygraphs measure blood pressure, breathing rate, sweating and other body changes.
James A. Levine, a study author and a Mayo Clinic endocrinologist, said the blushing seen around the robbers' eyes was the thermal signature of the primitive ``fright-flight response'' that arises when people lie.
Levine conceded the experiment was small but said the findings warrant ``aggressive investigation'' for potential security applications. His team is planning additional tests.
Frank Horvath, a professor of criminal justice at Michigan State University, was not impressed. He said the thermal imaging camera, like a polygraph, is only picking up physiological changes caused by anxiety. Such changes do not necessarily indicate guilt or innocence, he said.
And even if thermal imaging is comparable in accuracy to polygraphs, Horvath said it would not be suitable for rapid mass screenings. He noted that 25 percent of the test subjects who were lying eluded detection.