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In 2008, a judge in India convicted a woman of murdering her ex-fiance largely based on the results from an unusual kind of lie detection test: a type of brain scan called an electroencephalogram, or EEG. The suspect sat in a room with electrodes attached to her head as a voice read statements about the killing of Udit Bahrati, who died after eating arsenic-laced sweets. Based on the readout from the EEG, the test administrators said the suspect, Aditi Sharma, had “experiential knowledge” of Bahrati’s murder. The judge was swayed.
And in “Brains on Trial,” a PBS special hosted by actor Alan Alda that premiered earlier this month, brain scanning techniques to reveal memories, facial recognition, emotions, biases and intentions are examined through the prism of a fictional covenience story robbery. By showing how this technology can be used with witnesses, jurors, judges and possible perpetrators, the program offers a glimpse at how science and the law might intersect in the future.
But it's too soon for science to claim a victory against crime. Brain-based evidence is already used to determine the extent of brain injuries in, say, a workman’s compensation dispute or injury lawsuit. But current knowledge of what happens amid all that gray matter is far from the point where we can start distinguishing truth from lies and convict people for the confounding clues that our brains offer about what we think and what we have done, most neuroresearchers concede.
Your Mouth Says No, But Your Brain Says Yes
Despite their ubiquity on TV cop shows, polygraphs -- the “lie detectors” that measure changes in pulse, blood pressure and other physiological markers -- are largely scientifically discredited. But neuroscience is offering a different, potentially better path for separating truth from falsehoods: using changes in brain activity to measure recognition.
For example, a suspect could be shown a barrage of faces, one of which might be a suspected accomplice to or victim of a crime. His brain activity during this exercise could give away his relative familiarity with these people. Or he could be presented with pictures of a variety of settings, including the scene of the crime. If the brain activity patterns indicate that the suspect recognizes some aspect of the crime, that might be an important clue.
However, the researchers studying the cerebral architecture of recognition are quick to point out its limitations in the courtroom. Anthony Wagner, a cognitive neuroscientist at Stanford University, has pondered the applicability of his field to the legal system for years. In a guide to neuroscience for judges [PDF], most of Wagner’s chapter outlines the limitations of research on lie detection with functional MRIs (known as fMRIs).
“I tend to be conservative and urge caution,” Wagner says.
Just as there are ways to beat polygraph tests (controlling one’s breathing and staying calm seem to be the most popular and effective), Wagner thinks there could be countermeasures that could fool brain-scan-based lie detectors. The regions of the brain implicated in recognition and truth-telling will “light up” for other reasons as well: usually when a subject is making some sort of mental effort, like what's involved in trying to fool the test. So, if you want to beat a brain-scanning test, the trick might be as simple as doing something like arithmetic in your head to skew the results, or concentrating on something neutral – the taste of oatmeal, or the beige wallpaper in your dentist’s office -- when you’re presented with an incriminating image or statement.
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