Notes on improved lie detection technology

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This Wired article talks about two new technologies that are intended to detect when people are lying. Both technologies operate on the theory that lying involves different sections of the brain than telling the truth. So, by measuring the level of activity (via blood flow) to various parts of the brain, you may be able to tell when people are lying.

The technology that's been getting most of the detection here is functional magnetic resonance imaging. fMRI lets you detect the level of oxygenation of the blood in various parts of the brain, and at least in theory oxygen consumption is related to the level of activity. fMRI is already being fairly widely used in all sorts of neuro-psychological studies and I started hearing about its potential for lie detection a few years ago. fMRI, like all NMR-based imaging techniques, has two major drawbacks. The first is that you have to hold still or it doesn't work well (though motion compensation is getting better every year). The second is that because it involves very strong magnetic fields it's not safe if you have any substantial amount of ferromagnetic material in your body or on your person.

Another line of research is being pursued by Britton Chance at UPenn. The idea is blood flow again, but instead of using MRI, they're measuring blood flow using optical (near-infrared) spectroscopy. The upside is that you don't have to hold still and there's no metal concern. The downside is that you can only measure blood flow close to the surface of the skull, which may involve some loss of resolution. They're claiming a sensitivity of 95%, but it's not clear what the false positive rate is.

It seems like there are a bunch of open questions here. For starters, it's not clear what the error rate is. Given the low base rate of malfeasance, if you're going to use deception detection in screening settings, then even a low false positive rate will cause most of the positives to be false positives. One also needs to be concerned about the false negative rate. When people want to beat polygraphs, one thing they do is biofeedback training to see how to avoid generating the signals. Obviously, there are theoretical reasons why one might think it would be harder to beat a direct brain scan, but I haven't heard of anybody making a concerted effort to beat one, so we can't say for sure that it's impossible.

The other setting that people seem to be interested in using this technology is for interrogation. The idea seems to be that you would be able to tell when subjects are lying to you. That does seem useful, but it's important to remember that even if the technique works, it's only useful if people are actually trying to convince you they're telling the truth. That's probably true in criminal investigations but one of the problems our interrogators are having in Guantanamo, Afghanistan, and Iraq is that the subjects don't seem to care. Here's Chris Mackey and Greg Miller in The Interrogators:

When prisoners were questioned, everyone's name had been "lost" to fragile memory. There were no identifying features, no addresses, no telephone numbers. In the recesses of our minds where logic ruled, we knew it was impossible to have forgotten so much. But we were confounded by the utter directness of the lies. It wasn't a kind of cocktail party fib, easily seen through, easily peeled away. It was a mindless refutation of the obvious. And forbidden from punishing anyone for noncooperation, we couldn't do a damned thing about it. We could only gaze in disbelief and do our best to follow the school mantra: interrogators feign emotions, we never betray them.

I've also done some thinking about countermeasures, and I think that with some preparation—and one of the complaints from US interrogators is that their subjects have hasresistance training—you may be able to partially protect yourself against the fMRI technique. Remember that you can't use MRI on people who have metal implants, etc. This is a serious concern. I've had an MRI and when they found out I'd worked in a machine shop, they insisted on X-ray my eyes on the odd chance that I had metal slivers in them. It shouldn't be that hard to arrange for a few, thus requiring someone to perform (presumably nonconsensual) surgery before they can use this technique on you. Obviously, your captors could do the surgery, but that's a much bigger deal than just sticking your head in an MRI machine, especially if the implants are placed so that they're hard to remove without injuring the subject. This presumably isn't a problem with Chance's technique, and I haven't had time to think of any good countermeasures for that yet. Putting an IR-opaque plate in your skull would probably work, but I'm skeptical that it's practical on a large scale.

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2 Comments

I was watching the Discovery or Science channel a couple of weeks ago and they were demonstrating this device that detects activity in specific parts of the brain and using it as a lie detector. But it worked by detecting if the patient recognized a subject. Therefore, the patient didn't have to respond to any questions. If the interrogator asked, "Do you know Mr. X.", they could tell if the patient did or did not know Mr. X based on the feedback from the device.

I wish I could remember more details, but I'm sure I was also changing a diaper at the time.

Grumpy, are you thinking of a system like this one, which uses an EEG electrode cap (which is non-invasive) to pick up brain activity through the skull? The system looks for the P300 EEG component (basically a big positive signal that starts 300ms after the stimulus is shown), which is thought to correspond to surprise or novelty. Supposedly, if you generate a P300, then you've never seen the person/place/murder weapon before, but if you don't...well...you're in trouble :)


Unfortunately, Rosenfeld et al have already shown that there are fairly effective countermeasures for this sort of thing, which you can read about here. Also, I suppose you could just blink a lot; the associated muscle contractions generate so much noise that the rest of the signal would be obliterated. This isn't very subtle, but it would keep someone from figuring out what you knew.

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