Reconciling the opposing effects of neurobiological evidence on criminal sentencing judgments

Abstract

Legal theorists have characterized physical evidence of brain dysfunction as a double-edged sword, wherein the very quality that reduces the defendant's responsibility for his transgression could simultaneously increase motivations to punish him by virtue of his apparently increased dangerousness. However, empirical evidence of this pattern has been elusive, perhaps owing to a heavy reliance on singular measures that fail to distinguish between plural, often competing internal motivations for punishment. The present study employed a test of the theorized double-edge pattern using a novel approach designed to separate such motivations. We asked a large sample of participants (N = 330) to render criminal sentencing judgments under varying conditions of the defendant's mental health status (Healthy, Neurobiological Disorder, Psychological Disorder) and the disorder's treatability (Treatable, Untreatable). As predicted, neurobiological evidence simultaneously elicited shorter prison sentences (i.e., mitigating) and longer terms of involuntary hospitalization (i.e., aggravating) than equivalent psychological evidence. However, these effects were not well explained by motivations to restore treatable defendants to health or to protect society from dangerous persons but instead by deontological motivations pertaining to the defendant's level of deservingness and possible obligation to provide medical care. This is the first study of its kind to quantitatively demonstrate the paradoxical effect of neuroscientific trial evidence and raises implications for how such evidence is presented and evaluated.

Fig 1. Punishment change score by condition.

Bars denote the percentage change in time from individual baseline punishment rating across conditions, for their revised prison recommendation (dark grey) and recommendation for involuntary hospitalization (light grey). Statistically significant differences mirror the patterns described in H1-H4. Standard error bars shown.

Fig 2. Regression coefficients for the relationship between mental health status and prison sentence as explained by deontological concerns and consequentialist concerns.

Solid bold lines denote a significant relationship.