Describing Jurors' Personal Conceptions of Insanity and Their Relationship to Case Judgments

In a series of studies, prototype theory was applied to describe the nature, variability, and effect of jurors' conceptions of insanity. Specifically, (a) 80 jurors described the features of their prototypes of insanity, (b) 5 jurors combined similar features to develop a core set of features to measure individual differences, and (c) 135 jurors and 236 undergraduates completed measures of individual differences in prototypes and attitudes toward the insanity defense and the criminal justice system and rendered insanity case judgments. Results suggest that (a) jurors' prototypes of insanity cannot be reduced to legal or psychiatric constructs; (b) although there are marked individual differences in prototypes, there are 3 identifiable groups of jurors with prototypes that emphasize severe mental disability, "moral insanity," and mental state at the time of the offense; and (c) these prototypes are associated with case-relevant attitudes and affect the way in which jurors interpret case information and render verdicts. Implications for future research, legal reform, and the presentation of expert evidence are analyzed.