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By providing vignettes with manipulated scientific evidence, this research examined if including more or less scientific detail affected decision-making in regards to the death penalty. Participants were randomly assigned one of the two manipulations (less science and more science) after reading a short scenario introducing the mock capital trial and their role as jury members. Survey respondents were told that a jury had previously found the defendant guilty and they would now deliberate the appropriate punishment. Before being exposed to the manipulation, respondents answered questions pertaining to their prior belief in the death penalty, as well as their level of support of procedural justice and science. These questions provided a baseline to compare to their sentencing decision. Participants were then asked what sentence they would impose \u2014 life in prison or death \u2014 and how the fMRI evidence presented by an expert witness for the defense affected their decision. Both quantitative and qualitative measures were used to identify how the level of scientific detail affected their decision. Our intended predictor variable (level of scientific detail) did not affect juror decision-making. In fact, the qualitative results revealed a variety of interpretations of the scientific evidence used both in favor of death and in favor of life. When looking at what did predict juror decision-making, gender, prior belief in the death penalty, and political ideology all were significant predictors. As in previous literature, the fMRI evidence in our study had mixed results with regards to implementation of the death penalty. This held true in both of our manipulations, showing that despite the level of detail in evidence intended for mitigation, jurors with preconceived notions may still disregard the evidence, and some jurors may even view it is aggravating and thus increase the likelihood of a death sentence for a defendant with such brain abnormalities.
There is conflicting evidence regarding whether a biasing effect of neuroscientific evidence exists. Early research warned of such bias, but more recent papers dispute such claims, with some suggesting a bias only occurs in situations of relative judgment, but not in situations of absolute judgment. The current studies examined the neuroimage bias within both criminal and civil court case contexts, specifically exploring if a bias is dependent on the context in which the neuroimage evidence is presented (i.e. a single expert vs. opposing experts). In the first experiment 408 participants read a criminal court case summary in which either one expert witness testified (absolute judgment) or two experts testified (relative judgment). The experts presented neurological evidence in the form of functional magnetic resonance imaging (fMRI) data and the evidence type varied between a brain image and a graph. A neuroimage bias was found, in that jurors who were exposed to two experts were more punitive when the prosecution presented the image and less punitive when the defense did. In the second experiment 240 participants read a summary of a civil court case in which either a single expert witness testified or two experts testified. The experts presented fMRI data to support or refute a claim of chronic pain and the evidence type again varied between image and graph. The expected neuroimage bias was not found, in that jurors were more likely to find in favor of the plaintiff when either side proffered the image, but more likely to find for the defense when only graphs were offered by the experts. These findings suggest that the introduction of neuroimages as evidence may affect jurors punitiveness in criminal cases, as well as liability decisions in civil cases and overall serves to illustrate that the influence of neuroscientific information on legal decision makers is more complex than originally thought.