Effects of neuroimaging evidence on mock juror decision making

Abstract

During the penalty phase of capital trials, defendants may introduce mitigating evidence that argues for a punishment "less than death." In the past few years, a novel form of mitigating evidence-brain scans made possible by technological advances in neuroscience-has been proffered by defendants to support claims that brain abnormalities reduce their culpability. This exploratory study assessed the impact of neuroscience evidence on mock jurors' sentencing recommendations and impressions of a capital defendant. Using actual case facts, we manipulated diagnostic evidence presented by the defense (psychosis diagnosis; diagnosis and neuropsychological test results; or diagnosis, test results, and neuroimages) and future dangerousness evidence presented by the prosecution (low or high risk). Recommendations for death sentences were affected by the neuropsychological and neuroimaging evidence: defendants deemed at high risk for future dangerousness were less likely to be sentenced to death when jurors had this evidence than when they did not. Neuropsychological and neuroimaging evidence also had mitigating effects on impressions of the defendant. We describe study limitations and pose questions for further research.