Brain-Scan Lie Detectors Don’t Work

Tell the truth: you don’t think these things work, right?
Did you think they would?

I’ve told this story many times, but, hey, why not once more? I had a string of letters after my super-duper top secret clearance when I was in the Air Force, standard for crypto guys. To reduce the chance of spies in our midst the AF hopefully employed an outside contractor which ran lie-detector spy screenings.

This was back in the medieval torture days. Constricting straps around the chest and arms, wires leading everywhere, beeping machines, hot lights, absolute stillness required. First the “calibration”. The guy who stands behind you asks you to think of the number seven, after which he says he’ll ask you if you’re thinking of the numbers one through ten and that you’re to say “No” to each, even seven.

So you do. After which he shows you a squiggle that looks exactly like every other squiggle and says, “See? That’s where you ‘lied’ and said you didn’t think of seven.” If you’re smart, you agree. Why cause trouble?

The questions come and eventually stop. After which, invariably, the guys says, “Sergeant Briggs. Looks like we have a little trouble with one of the questions. Think you can help me out with that?” Any but a fool says, “Huh? I don’t know.” Play dumb. Maybe the guy fishes around a bit, but if you sit happy and stupid, he lets you go.

Now I have seen pathological liars go through this process and pass (Shawn, remember JK?). Every one of the big-name spies you’ve heard about, and all the small ones you haven’t, also passed. Conclusion: lie detectors don’t work.

But that was the old stuff. Now they’re doing brain scans, which is as sciencey and science gets, right? The whitecoats figure all they have to do is to peer at the right spot in the brain, the spot where lies originate, ask you a question, and then wait to see if the spot “lights up.” If so, you’re lying, n’est-ce pas?

Or maybe not the lie area of the brain, but how about the guilt lobe? Liars always feel guilty telling lies, don’t they? Seems fMRIs ought to be able to sniff out guilty versus non-guilty brains. Maybe the color on the screens of the brain-scanning machines goes green, or it could be chartreuse.

Lying is simple. It’s the telling of something believed to be false. It is the will willfully acting at variance to the truth. Or, no. How can it be willed action? Since lying has to begin in the brain, as the philosophy of materialism asserts, and there is no will only the illusion of the same, leaving aside the question of “who” is doing the “illusioning,” we should, at least in principle, be able to section the little grey cells until we can spot a fabrication under the microscope.

Anyway, the Pacific Standard (tag-line “The Science of Society”) reports on yet another new study which says brain-scan lie detectors don’t work because “perpetrators” can “suppress crime memories.” The press release is more sedate “people can intentionally and voluntarily suppress unwanted memories.”

Which we did not need science to tell us. That people can forget has been known long before anybody invented a computer. Why, not only can people suppress unwanted memories, they can forget all sorts of things. Just ask the Blonde Bombshell if Yours Truly can remember to take the dishes out the washer. But if you were to ask me, I’d say, sure I did it. At least, I think I did. I seem to recall it.

Can’t go much by the study, which is another in a long string of highly artificial situation experiments. This had people simulate crimes and pretend not to remember them, which some could do. At least according to the brain-scan sniffers, which couldn’t find the suppressed memories of pretend crimes.

In real crimes if there wasn’t indisputable corroborative proof, there would be a person’s word against some colored pictures, which folks like me could show are easy to misinterpret. Some people would believe the pictures but have doubts, others wouldn’t believe. We’re in the same spot we’ve been in forever. Some people crack under questioning, some don’t. Some lie, some don’t.


  1. Sheri

    Pathological liars have no guilt (see Obama for reference…..) so you cannot detect a pathological liar except through careful, long-term observation. After a while, they have problems remembering what lies they told to whom.

    Then there are persons such as my mother (now deceased, so she can’t be incriminated at this point) who simply remembered things as she wanted them to be. Even when confronted with photographic evidence, she refused to believe she was wrong. She wasn’t lying–she simply bent reality to her liking. In this case, even a mind reader, if we had such a thing, would not know that the information was factually inaccurate. My guess is such a person would make a wonderful spy, believing what they want to be the truth is the truth.

  2. DAV

    How can it be willed action?

    It’s only a short step from “Free Will” to “Free Willy” but that’s another wail.

  3. DAV

    But seriously, the lie detector measures bodily reaction and the existence of those actions are supposed to correlate with lying. The real problem is how to correlate lying with anything. There’s a big difference (I would think) between a superficial lie and an I-don’t-wanna-get-caught one. The latter is really hard to produce in a lab.

  4. DAV


    Precisely. Creative interpretation of the question couldn’t hurt either. Particularly if you can generate terror after every question posed. There are also tricks for changing your blood pressure.

    The test (calibration) questions are more to convince you the machine can tell than they serve as calibration. The real lie detector is the guy running the machine using Syense (thanks for that 49er) to justify his conclusions.

  5. MattS

    The reason courts don’t accept polygraph tests is that properly controlled studies have shown that the machine is no better at picking up lies than the operator is without the machine.

    The reason agencies continue to use them for interrogations is for the intimidation/placebo effects. If the person being interrogated believes that the machine works, they they will either tell the truth or do something to give themselves away when they lie.

  6. Ray

    I gave the poly examiner fits. I used to work at Field Station Berlin and Berlin was 120 miles inside East Germany. We also worked with the British and Germans. The poly examiner would ask questions like, have you ever traveled to any communist country? I would respond that I used to live in one. They would ask if you had any contacts with foreign intelligence agents and I would reply, of course. I had to go into lengthy explanations. One time when I told the examiner that I worked in Berlin, He solemnly informed that it was in East Germany. I was tempted to act surprised and say, no kidding? Instead I just kept my mouth shut.

  7. MattS


    Answer every question with “42”. 🙂

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