Lie detectors: tomography against terror

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Lie detectors: tomography against terror
Lie detectors: tomography against terror

Tomography Against Terror

Terrorists lie, but their brains know the truth. One can snatch the knowledge from him. The magnetic resonance tomograph is, as one could read these days, the ultimate weapon in the fight against terrorism. Or not?


It's an ancient dream of mankind to spot liars with absolute certainty. Many methods were tried: In medieval Rome, for example, this was the Bocca de la Verita. Whoever put his hand in the gargoyle's open mouth lost it if he lied at the same time. However, according to tradition, some of those involved had so much doubts about how it worked that they immediately helped out with the sword themselves. Torture is and has been considered a tried and tested means of finding the truth since time immemorial. However, moral concerns aside, it serves its purpose rather poorly, as it often persuades its victims to make false confessions. So more suitable methods are needed.

In the 1950s, a scientifically based method began its triumphant advance: polygraphy. The lie detector uses the body's reactions to stress as an indication of the truthfulness of statements. Because when lying, so the theory goes, people are more excited than usual, and this is also reflected in physiological measures: the heartbeat accelerates, blood pressure rises, the liar sweats more profusely. All of this can be measured and from the changes experts then conclude which statements are true and which are lies. However, as "Image" as the method itself is the dispute among scientists about its reliability. alt="

For several years, imaging techniques that make the activity of the brain visible have become the focus of interest as a means of finding the truth. For example, Daniel Langleben from the University of Pennsylvania is now investigating the ability of a computer to unmask lies from a total of 22 test participants based on brain activity recorded by a magnetic resonance tomograph. The test participants were given two playing cards and were then asked to deny possession of one and confess to the other. If they managed to deceive, they were offered a $20 reward. During the first rounds, the computer practiced, always finding out whether the subject was fibbing or not. From this he developed an algorithm with the help of which he tried to uncover subsequent lies. When he subsequently applied this to the same subjects, he predicted with an average of 99 percent probability whether they were currently cheating [1].

Developed a new high-tech method in the fight against terror?

On closer inspection, however, the result is not that exact: The precision of the prediction only applied to individual subjects. However, if the computer tried to infer other people from the test group, it was often wrong. More precisely, he imputed the opposite in every fifth case in which the participants told the truth [2]. A high value given the consequences that such an error could have for an accused in reality if the procedure is actually used in a trial. For comparison: With other scientific methods such as DNA analysis, values of less than 99 percent reliability are considered too imprecise in court.

And what happens if the suspect doesn't play along with the calibration procedure but deliberately tries to fool the computer? In the end, the 99 percent would not be attainable when the decisive question comes after the attempted assassination. And if he disputes in court that the values determined for other people apply to him, nobody can prove the opposite without knowledge of generally applicable laws - in case of doubt for the accused. Contrary to the assertion that the method is immune to any influence, there is no proof that people cannot learn to use the so-called biofeedback method to fool the computer by deliberately controlling their brain waves.

In general, the previous test scenarios seem far from reality [3]. A subject who is asked to lie and is even rewarded if he is successful is in a fundamentally different situation than an alleged terrorist or criminal who faces severe punishment, if not death. How does this load affect the measurement? It is not even known what aspect of the lie the brain activity reflects: is it really the effort to hide the truth? Or do you see the sense of injustice when lying – which was certainly not very pronounced in the experiment? How does the brain of people who lack one, such as psychopaths or those who have been indoctrinated, react in contrast to Langleben's students? All questions that would have to be considered before big headlines.

The search for the one center of lies in the brain has so far been unsuccessful. The model published by Langleben for predicting lies includes changes in 14 brain regions. Studies by other research groups have also not produced a clearer or more uniform picture so far: in addition to an above-average activity of the prefrontal cortex found in almost all studies, there was a significant correlation in almost every brain area involved in cognitive performance in some research work. The conclusion that the group draws about Langleben sounds correspondingly sobering: overall, lying is more exhausting than telling the truth, which is why more activity can be observed in the brain during the process – but there is no clear pattern.

Langleben therefore expresses doubts about the soon usability of imaging methods as lie detectors and calls for further detailed investigations. Under no circumstances, he warns, should scientists and decision-makers allow themselves to be guided by the euphoria about the new methods and put them to use before they are really mature and standards regarding application and evaluation by specially trained experts exist. It may be that one day this will succeed, but there is still a long way to go to celebrate a new weapon in the fight against terror.

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