That’s a terribly constructed title, I know, but bear with me. A couple of weeks ago I blogged about a courtroom case in Tennessee where the defense was trying to introduce fMRI to the courtroom as a way of proving the defendant’s innocence (his brain, apparently, showed no signs of guilt). The judge’s verdict is now in, and…. fMRI is out. In United States v. Lorne Semrau, Judge Pham recommended that the government’s motion to exclude fMRI scans from consideration be granted. That’s the outcome I think most respectable cognitive neuroscientists were hoping for; as many people associated with the case or interviewed about it have noted (and as the judge recognized), there just isn’t a shred of evidence to suggest that fMRI has any utility as a lie detector in real-world situations.
The judge’s decision, which you can download in PDF form here (hat-tip: Thomas Nadelhoffer),Â is really quite elegant, and worth reading (or at least skimming through). He even manages some subtle snark in places. For instance (my italics):
Regarding the existence and maintenance of standards, Dr. Laken testified as to the protocols and controlling standards that he uses for his own exams. Because the use of fMRI-based lie detection is still in its early stages of development, standards controlling the real-life application have not yet been established. Without such standards, a court cannot adequately evaluate the reliability of a particular lie detection examination. Cordoba, 194 F.3d at 1061. Assuming, arguendo, that the standards testified to by Dr. Laken could satisfy Daubert, it appears that Dr. Laken violated his own protocols when he re-scanned Dr. Semrau on the AIMS tests SIQs, after Dr. Semrau was found “deceptive“ on the first AIMS tests scan. None of the studies cited by Dr. Laken involved the subject taking a second exam after being found to have been deceptive on the first exam. His decision to conduct a third test begs the question whether a fourth scan would have revealed Dr. Semrau to be deceptive again.
The absence of real-life error rates, lack of controlling standards in the industry for real-life exams, and Dr. Laken’s apparent deviation from his own protocols are negative factors in the analysis of whether fMRI-based lie detection is scientifically valid. See Bonds, 12 F.3d at 560.
The reference here is to the fact that Laken and his company scanned Semrau (the defendant) on three separate occasions. The first two scans were planned ahead of time, but the third apparently wasn’t:
From the first scan, which included SIQs relating to defrauding the government, the results showed that Dr. Semrau was “not deceptive.“ However, from the second scan, which included SIQs relating to AIMS tests, the results showed that Dr. Semrau was “being deceptive.“ According to Dr. Laken, “testing indicates that a positive test result in a person purporting to tell the truth is accurate only 6% of the time.“ Dr. Laken also believed that the second scan may have been affected by Dr. Semrau’s fatigue. Based on his findings on the second test, Dr. Laken suggested that Dr. Semrau be administered another fMRI test on the AIMS tests topic, but this time with shorter questions and conducted later in the day to reduce the effects of fatigue. … The third scan was conducted on January 12, 2010 at around 7:00 p.m., and according to Dr. Laken, Dr. Semrau tolerated it well and did not express any fatigue. Dr. Laken reviewed this data on January 18, 2010, and concluded that Dr. Semrau was not deceptive. He further stated that based on his prior studies, “a finding such as this is 100% accurate in determining truthfulness from a truthful person.“
I may very well be misunderstanding something here (and so might the judge), but if the positive predictive value of the test is only 6%, I’m guessing that the probability that the test is seriously miscalibrated is somewhat higher than 6%. Especially since the base rate for lying among people who are accused of committing serious fraud is probably reasonably high (this matters, because when base rates are very low, low positive predictive values are not unexpected). But then, no one really knows how to calibrate these tests properly, because the data you’d need to do that simply don’t exist. Serious validation of fMRI as a tool for lie detection would require assembling a large set of brain scans from defendants accused of various crimes (real crimes, not simulated ones) and using that data to predict whether those defendants were ultimately found guilty or not. There really isn’t any substitute for doing a serious study of that sort, but as far as I know, no one’s done it yet. Fortunately, the few judges who’ve had to rule on the courtroom use of fMRI seem to recognize that.