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You Can’t Hide Your Lying Brain (or Can You?)

Earlier this week Wired reported that a Brooklyn lawyer wanted to use fMRI brain scans to prove that his client was telling the truth. The case itself is an average employer-employee dispute, but using brains scans to tell whether someone is lying—which a few, small studies have suggested might be useful—would set a precedent for neuroscience in the courtroom. Plus, I’m pretty sure they did something like this on Star Trek once.

But why go to all the trouble of scanning someone’s brain when you can just count how many times the person blinks? A study published this month in Psychology, Crime & Law found that when people were lying they blinked significantly less than when they were telling the truth. The authors suggest that lying requires more thinking and that this increased cognitive load could account for the reduction in blinking.

For the study, 13 participants “stole” an exam paper while 13 others did not. All 26 were questioned and the ones who had committed the mock theft blinked less when questioned about it than when questioned about other, unrelated issues. The innocent 13 didn’t blink any more or less. Incidentally, the blinking was measured by electrodes, not observation.

But the authors aren’t arguing that the blink method should be used in the courtroom. In fact, they think it might not work. Because the stakes in the study were low–no one was going to get into any trouble–it’s unclear whether the results would translate to, say, a murder investigation. Maybe you blink less when being questioned about a murder even if you’re innocent, just because you would naturally be nervous. Or maybe you’re guilty but your contacts are bothering you. Who knows?

By the way, the lawyer’s request to introduce the brain scanning evidence in court was rejected, but lawyers in another case plan to give it a shot later this month.

(The abstract of the study, conducted by Sharon Leal and Aldert Vrij, can be found here. The company that administers the lie-detection brain scans is called Cephos and their confident slogan is “The Science Behind the Truth.”)

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