Liar, Liar – Part III: Mach-lies

– By Syeda Qudsia, NUST Science Blog.

So you can use visual cues to detect lies… and you can become an expert in spotting microexpressions as well to catch the person. But is it always that easy?

Of course it’s not. It is one of the most difficult things to detect. If you become really, really good at it, you may get it right for about, may be, 60% of the times… which is only 10% above your chances, by default, of correctly guessing false from truth according to probability theory. That shirt of yours which got stolen? Looks like you might have to put your suspects through a series of procedures before you can be deadly sure of who’s lying and who’s not; possibly taking them through magnetic resonance imaging and poring over their brain scans… Ouch.

A number of instruments have been developed to minimize the human error associated with lie detection, relying on the fact that an act of deception is likely to produce some physiological signs, which may be change in inhalation-exhalation rate, blood pressure, pupil dilation and the like. The question is: how reliable these instrument are in their performance?

The simplest of them would be to use a questionnaire like the control-question-test-guilty-knowledge-test and record the overall physiological response of your liar. Or you could go for an electroencephalogram to see how the electrical impulses play around in the heads of liars.

The Lie-Detector

The most well known of lie detection equipments is the “lie-detector”, a.k.a. polygraph. Interestingly, nobody believes the lie-detector. It goes for involuntary responses associated with the vile act of lying, like heart rate, skin conductivity, blood pressure, and muscular movement. Well, the fact is that all the liars know, and the good ones have enough control to deceive the lie-detector, whereas some of the innocent ones may get so nervous and stressed out during the test that they get falsely accused by the device. So, really, you additionally have to make sure that the lie-detector is not lying to you.

But if you are dead serious about it and want to corner down your culprit with 90% plus sureness, go for an MRI (Magnetic Resonance Imaging). MRI scanners are generally used for scanning soft tissues of the bodies to detect abnormalities (just like an X-ray, but X-rays image your hard tissues only, and use radiations instead of magnetic fields). Now, MRI scanners are finding their way into “deception-detection” due to their extreme sensitivity to detect activity changes in specific areas of the brain.

Put in your suspect.

The procedure is to strap down your suspect to a stretcher and feed them to the hollow center of a magnet. As the scanner is poking around in their brain, you can run a series of control questions and test questions on a screen inside the set up and look for the changes is brain activity. The theory is that when a liar is busy concocting a lie, then no matter how well they control their physiological phenomena, they can never hide the sudden rise in activity in certain regions of their brain, which is mapped by monitoring the increased flow of oxygenated blood to that region. It is totally involuntary and unstoppable, but the use of MRI for lie-detections is still pretty new, and it hasn’t yet been approved for criminal investigation.

Lie detection can come in handy once in a while, and to some extent, it can be practiced as well. But the truth of the matter is not to be very trustworthy of the results if you are not going for an MRI – and MRI is still in the process. For now, I hope for the MRI… and for your shirt.


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