People are great liars. We are so good at it, in fact, that it’s incredibly difficult to create a machine that can accurately identify whether a person is lying. While Polygraph tests, which record a person’s heart rate, respiratory rate and sweat patterns, are pretty good at distinguishing fact from fiction, they aren’t good enough to be used for tendering evidence in Australian courts. The next generation of lie detectors, however, use MRI scans and are up to 90 per cent accurate, which could very well make the grade for legal use.
Functional MRI scanners detect the activity of neuron firing in your brain. They measure oxygen levels; the more oxygen in a particular area of the brain, the more neurons are firing. Brain scans that compare individuals who are lying and telling the truth have found five specific regions in the brain that keep lighting up when a person is being dishonest.
Dr. Daniel D. Langleben at the University of Pennsylvania has known for 10 years that MRIs could be used for lie detection. “If there is a behaviour that you are consciously aware of, it should have a brain correlate,” he says. If we know that we are lying, it should be reflected in our brain activity, and detected on a scanner.
When we lie, we give an object related to our deceit more attention, or salience, and this change is noticed on a scanner. “If you stole a green apple, and I showed you pictures of apples, but there is only one green apple, you will have a higher physiological response to the green apple because it is given more salience,” explains Langleben. While we don’t interrogate too many people for apple-poaching, scans could be used to show photos of victims, or criminal abetters.
Unfortunately, scans detecting salience aren’t 100 per cent accurate. “It is kind of vague because what if you love green apples, or you have an orchard of green apples?” says Langleben. In these cases, your brain will give apples more attention, and light up in certain areas associated with lying, even where you are telling the truth. To combat this, researchers also use control tests to detect lies.
Interrogators ask people known facts (What is your name?) and unknown facts (Did you steal the apple?) and compare the scanner results. Depending on the study, MRI scanners have been shown to accurately predict lies 76 to 90 per cent of the time. Plus, with most studies only testing around 20 people, larger clinical trials need to be conducted before Australian courts would consider admitting evidence from MRI lie detectors.
“It would have to be very reliable before the court would even consider it,” says Andrew Palmer at the Law Faculty of The University of Melbourne. According to Palmer, people would have to voluntarily submit to the MRI scan because it is an invasive test.
Although MRI lie detectors are accurate, there are still ways to cheat the system. But, according to Langleben, “Cognitive counter measures are detectable in their own right, and therefore not that effective.” While the five areas of the brain associated with lying might not light up if you were cheating the system, other areas of the brain would, and these would be detected by the MRI.
Find out more about how it works in the July 2009 edition of Popular Science, on sale now!
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