The purpose of this study was to examine mock jurors’ decision making in insanity cases. Specific instructions (vs. typical) juror instructions were tested to increase jurors’ comprehension of verdict options and reduce the effects of preexisting attitudes and reliance on cognitively biased thought processes in their legal decision making.

The specific instructions in this study were inspired by Fuzzy Trace Theory, which holds that simple language and visual aids that convey the ‘gist’ of complex information can help people make better decisions (Reyna & Brainerd, 1995). Participants (N= 496) were randomly assigned to one of two juror instruction conditions (specific vs. typical). All participants read a 10-page insanity defense case vignette, and were tasked with reaching a verdict. They were provided with 5 verdict options: Not Guilty, Guilty, and three different insanity options (Not Guilty by Reason of Insanity, Guilty but Mentally Ill, Guilty Except Insane). Results supported the hypothesis that jurors who received specific (vs. typical) instructions would comprehend more information about the available verdicts, and would be more likely to choose an insanity defense verdict. As expected, jurors’ preexisting attitudes toward the insanity defense influenced their verdicts. Although it was hypothesized that increasing jurors’ understanding would result in them relying less on their attitudes and motivated reasoning processes in reaching their legal judgments, the evidence did not support this. Results suggest more specific instructions that includes information about outcomes is preferred by jurors, and that they are better able to understand and perform their duties when provided with more useful information. However, further research is needed to identify methods for helping jurors rely less on biased reasoning processes in their legal judgments.