Is it hard to beat a polygraph

Committed to the "truth"

If you lie, you get nervous. The heart starts beating faster, breathing changes, hands sweat. A classic lie detector, also known as a polygraph, continuously measures and records these physiological parameters. For experts, these patterns provide clues as to when someone reacts tense during a survey. But there are two fundamental problems. Does nervousness automatically mean that the respondent is lying? And how should you use the device in practice if you first have to wire up each person for the test? Hassan Ugail from the Center for Visual Computing at the University of Bradford, UK, is currently working on a new lie detector. One who is suitable for everyday use - and who should more reliably distinguish whether someone is actually lying or is simply excited.

"Our idea was to develop an alternative to the classic polygraph. The biggest problem with this is that the tested person has to agree with the measurement of blood flow, heartbeat, skin conductivity and so on. In addition, you have to have the measuring devices directly on the body of the person. So our idea was to develop a polygraph that is non-invasive. "

For his development, the mathematician combined a normal video camera with a thermal imaging camera. While Hassan Ugail asks the test subjects, the high-resolution thermal imaging camera records the blood flow around the eyes - so precisely that the researcher can analyze individual blood vessels.

"We first look at a normal situation when a person is relaxed and telling the truth - and then we look at the blood flow around the eyes and create a temperature profile for that part of the face. Then we check the blood flow again, in a situation where the person may be lying to us and calculate the difference. When we do that, not only are we looking at an increase in temperature - it could also be a decrease - we are looking at the variation. "

This comparison reduces the risk of mistaking excitement for a lie. Hassan Ugail complements the individual temperature profile with a facial analysis method developed by psychologists. In the recordings of the video camera, the scientist examines every beginning of an emotional expression in the facial expressions of the participants - and can often discover them even when an emotion is suppressed and can only be seen for milliseconds. The use of the cameras is practical because the mathematician can position them inconspicuously or even invisibly. This prevents the respondent from becoming nervous himself or trying to control his behavior due to the measurement technology - frequent reproaches to the old polygraph. The combination of both techniques also protects against fraud.

"Some actors might be fooling our face analysis - but that's why we use two systems and don't just rely on the visual area. There, deception is still possible, for example you can try not to show any facial expression and just talk. But at the same time we see the thermal image, and it is very difficult to control the blood flow in the face, the heartbeat and so on .. You can see the discrepancy in the thermal image quite easily, quite nicely.

So far, Hassan Ugail has tested 40 subjects in the laboratory. He was able to correctly identify 75 percent of those who lied. But some were wrongly accused of lying, while others got away with lying unrecognized. The mathematician is currently working on refining his method.

"The next step for us is to increase the success rate to 90 percent - that is, to collect more test results and improve our algorithm. And then we would like to develop a commercial product out of it that will hopefully be used by the police, border controls or in other interview situations finds. "

The new lie detector is currently also supporting the British border patrol at an airport on a trial basis. Hassan Ugail is not allowed to reveal any details. But he knows that in the future, despite all his efforts, his detector will not be able to correctly distinguish between truth and untruth. Because both are relative quantities, not only for the measuring devices, but also for people themselves. His goal is therefore not to establish the new lie detector as evidence. Its development should be a decision-making aid - no more, but also no less.