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  • Brain Imaging and Courtroom Deception
  • Rebecca Dresser (bio)

Deception is an all-too-common human activity, one that succeeds because we cannot always detect it in others. It complicates all sorts of human decision-making, including attributing guilt for criminal offenses. The law relies on human fact-finders to determine whether criminal defendants claiming innocence, as well as witnesses testifying about a case, are telling the truth. But the fallibility of human lie detection has fueled the search for a more accurate replacement.

Scientists have developed new approaches to lie detection that use a brain scanning technique called functional magnetic resonance imaging (fMRI) to evaluate whether someone is lying. In experimental settings, researchers have found that different parts of the brain are active when subjects are giving truthful or deceptive answers. The advantage of fMRI is that it can discern the blood flow changes that indicate changes in brain activity. The technique’s developers claim that it is much more accurate than the polygraph, the old-fashioned lie detector that relies on increases in blood pressure, pulse rate, and other measures of autonomic arousal to indicate whether someone is telling a lie.

Legal authorities have been skeptical of the polygraph’s value, and courts usually exclude test results on grounds that the accuracy rates are too low. Enthusiasts hope that courts will be more receptive to fMRI lie detection techniques. But two recent court decisions suggest that these techniques are far from ready for courtroom use.

Questions of Reliability and Probative Value

In 2010, two judges issued opinions addressing the admissibility of testimony about fMRI lie detection test results. Both determined that the test results were inadmissible. The most extensive analysis comes from Tennessee Federal Magistrate Judge Tu Pham, who conducted a so-called Daubert hearing to determine whether test results should be admitted in the trial of Lorne Semrau, a psychologist charged with health care fraud.1

Daubert hearings are conducted to determine whether scientific or other technical evidence meets the admissibility criteria set forth by the U.S. Supreme Court in Daubert v. Merrell Dow Pharmaceuticals.2 In Daubert, the Court said that Federal Rule of Evidence 702 requires trial judges to determine whether expert testimony is both reliable—supported by scientifically valid reasoning or methodology—and relevant—applicable to the specific issue the court must resolve. Judges making these determinations could consider: (1) whether the scientific technique is testable and whether it has been tested; (2) whether the technique has been subjected to peer review and publication; (3) the technique’s known or potential error rate; (4) whether there are standards governing the technique’s application; and (5) whether the scientific community accepts the technique.

The defendant in United States v. Semrau wanted to submit test results from an fMRI lie detection method developed by a company called Cephos. At the Daubert hearing, Magistrate Pham accepted testimony from three expert witnesses, including the chief executive officer of Cephos, a scientist who helped develop the Cephos lie detection method. The magistrate found that the Cephos test had been studied in laboratory experiments and the results published in peer-reviewed journals. But the technique fared less well when he turned to the remaining Daubert factors.

Although the Cephos CEO testified that published studies reported an accuracy rate of about 90 percent for the test, another expert at the hearing said those studies were too small to provide valid data. More importantly, the studies were conducted in circumstances quite different from those present in an actual criminal case. Ironically, Magistrate Pham could turn to articles written by the CEO and members of the Cephos scientific advisory panel for a discussion of the differences. First, study subjects failed to represent the general population—none of the studies included subjects as old as the defendant, nor did they include people on medication or those with medical or psychiatric conditions. Second, they all involved “researcher-induced” deception about recent events (Semrau’s alleged fraudulent conduct had occurred six to eight years before his fMRI test). The brain activity of subjects instructed to lie about recent events in an experimental setting could differ from that of a person lying about past events in an...


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pp. 7-8
Launched on MUSE
Open Access
Archive Status
Archived 2012
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