Evidence of Lies and Rules of Evidence: The Admissibility of fMRI-Based Expert Opinion of Witness Truthfulness

Neuroscientists are exploring intriguing technology that some claim will revolutionize the jury’s search for truth in American courtrooms. Functional Magnetic Resonance Imaging (fMRI) seeks to correlate brain activity with cognitive function. Current research with regard to lie detection indicates that in laboratory studies neuroscientists have achieved accuracy rates in excess of 90% in identifying deception and verifying truth in study participants. But will it work in the real world forensic setting? How does this new technology fit within the context of the rules governing the impeachment and rehabilitation of witnesses? Does the new technology meet the reliability standards demanded of expert scientific opinion? Will professional opinions on witness truthfulness help the jury in its fact-finding role? Or, will this new technology confuse and confound the jury in its essential task of reaching a verdict? These are but a few of the issues surrounding this emerging and exciting technology. The legal literature to date has primarily focused upon whether the technology can satisfy the Daubert factors when offered to verify truth and to detect deception or whether it should be admitted even if it fails to meet the exacting standards of FRE 702. Some commentators argue that fMRI-based expert opinion testimony on witness truthfulness should be admitted because the laboratory results are more accurate than a lay juror’s ability to detect lies unaided by technology. fMRI lie detection may not be totally reliable, the argument goes, but since it is better than what twelve people with a driver’s license can do, it should be admitted. What the literature has not done, however, is analyze fMRI-based expert opinion testimony on witness truthfulness in the context of all the rules that regulate impeachment and rehabilitation of witnesses, as well as the rules governing the reliability of scientific expert testimony. This paper is an attempt to fill that gap and provide a comprehensive analysis of the admissibility of this new technology for lie detection or truth verification. While the fMRI study might detect “lies” in the lab, the rules of evidence as applied in US courts consider the citizens of the community selected to sit on the jury the “lie detector” in the courtroom. Three recent decisions, one in a Federal court applying the Federal Daubert standard, one in a New York state court civil case, and another in a Maryland state criminal proceeding applying the Frye general acceptance test, rejected expert testimony based on the results of fMRI scanning.Using these three cases as the backdrop for analysis, I identify thirteen major problems that impose significant obstacles to the admission of this sort of testimony. I present this baker’s dozen of issues under four major categories: (1) the regulation of impeachment and rehabilitation of witnesses, (2) the requirement that expert testimony help the jury to understand the evidence or decide a fact in issue; (3) the rule requiring expert testimony to be based upon reliable principles and methods; and (4) the balancing of unfair prejudice and probative value of the opinion testimony. All four of these categories impose serious obstacles to the admission of fMRI-based expert opinion testimony of witness truthfulness.