Hypothetical Courtroom: Influence of Expert Witness Testimony on Jurors’ Decision-Making

Abstract

Jurors’ decision-making is shaped by social and psychological factors that may create bias, particularly in cases involving psychopathic defendants. The present study examined how a hypothetical defendant’s perceived psychopathy, the type of scientific evidence presented (neuroimaging vs. only verbal descriptions), the gender of the expert witness, and the expert’s use of artificial intelligence (AI) affect jurors’ decisions. Participants read one of four mock trial vignettes involving a psychopathic defendant and then evaluated the defendant’s guilt, recommended sentence length, and the credibility of the expert witness. Results indicated that confidence in the expert significantly decreased after participants were informed that the expert had used AI. A significant main effect of evidence type suggested that participants in the neuroimaging condition perceived the defendant as lower in psychopathic traits compared to those in the verbal description only condition. No significant main effects were found for expert gender or sentencing severity in the factorial analyses. However, perceptions of psychopathic traits were positively correlated with sentencing recommendations, guilt perceptions, and confidence in the expert witness. Participants who perceived the defendant as higher in psychopathy recommended harsher sentences and expressed greater confidence in the expert. These findings exemplify the complex influence of technological disclosure, biases, and character-based judgments in juror decision-making