How disorder onset controllability moderates the impact of biological arguments on judgments of criminal responsibility

In recent years, the use of biologically based (neurological, neuropsychological, genetic) evidence in criminal trials as support for claims of mental impairments among offenders has increased in popularity. However, research on how exposure to those arguments affects jury decision-making remains unclear. Specifically, arguments rooted in biology sometimes mitigate and sometimes aggravate judgments of criminal responsibility for mentally ill offenders, and this discrepancy seems to stem from the specific conditions by which that disorder was acquired. The following study’s aim was to uncover the precise mechanism(s) behind this elusive effect. Utilizing a 2x2 between subjects experimental design, participants were presented with a hypothetical crime summary involving an offender with either an onset controllable or uncontrollable mental disorder. Ratings of criminal responsibility and other variables hypothesized to function as mediators were obtained after presentation of a prime supporting either a biologically deterministic or free will argument for human behavior in general. Results indicated that when the defendant’s disorder was the result of the his own actions (onset controllable), a biological prime decreased judgments of criminal responsibility; however, when the disorder was caused by factors out of his control (onset uncontrollable), the prime increased judgments of criminal responsibility. An examination of several possible mechanisms finds the effect mediated by the perception of control the defendant could have had over his own actions at the time of the crime. These results suggest that perceptions of behavioral control are an important contributor to jurors’ formation of criminal responsibility judgments when an offender possesses a mental illness; and arguments advocating a biological basis for human behavior reliably affect blame attribution, suggesting that a societal shift in the perception of free will as a result of increased exposure to biology in general may alter the framework of criminal responsibility judgments.