Despite much psychological research regarding jury decision making, surprisingly little is known about the deliberation process that gives rise to jury verdicts. We review classic jury decision-making research regarding the importance of deliberation and more recent research, investigating deliberation and hung juries, that challenges the view that deliberation does not have an important impact on verdicts. We advocate greater attention to potential cognitive processes during deliberation that might explain the transition between predeliberation preferences and a jury's ultimate verdict. We then review cognitive work in the group context generally, and the jury context specifically, illustrating the promise of a cognitive perspective on jury deliberation. Finally, we identify cognitive phenomena likely to be particularly valuable in illuminating deliberation behavior.
Psychologists have learned a great deal about juries from research conducted over the past 50 years. Much of that research has directly contradicted claims made by courts about jury functioning. For example, writing for a plurality of the United States Supreme Court in Johnson v. Louisiana (1972), Justice White concluded that a unanimous decision rule was not required because a "majority will cease discussion and outvote a minority only after reasoned discussion has ceased to have persuasive effect or to serve any other purpose." In contrast, empirical research has shown that a nonunanimous decision rule can undermine attention to minority arguments (Diamond, Rose, & Murphy, 2006; Nemeth, 1977; Saks, 1977). Although some courts do not embrace research findings from psychological research on the jury, other courts welcome them. For example, evidence on the way jurors use the opportunity to submit questions for witnesses during trial helped to persuade the court in S.E.C. v. Koenig (2009) of the benefits of approving that procedure (Diamond, Rose, Murphy, & Smith, 2006).
Although many advances have been made in understanding jury deliberations, several important questions remain that cognitive psychology is in a strong position to address. We know that the distribution of individual jurors' predeliberation verdict preferences is a strong predictor of the jury's final verdict, but not what makes the majority position so influential or the circumstances under which minorities are likely to prevail. Are majorities influential because minority jurors simply succumb to normative influence or because of vote changes resulting from cognitive restructuring or group-level cognitive processes (e.g., memory pooling and error correction)? What happens differently during deliberations when a jury is hung or a minority convinces the majority to change their vote?
These unanswered questions call for the investigation of the role played by cognitive constructs, such as recall for testimony, memory pooling, error checking, collaborative false recall, and heuristics. Thus, we call for cognitive psychologists to broaden their inquiry from the topic of individual jurors to that of the deliberation process. We begin by briefly reviewing what psychologists have learned about the deliberation process. We then describe a set of remaining questions that would benefit from cognitive psychologists' attention.
Research on Jury Decision Making: The Production of Verdicts
Jury decision-making research began in the 1950s with the Chicago Jury Project. In their landmark field study, Kalven and Zeisel (1966) conducted a judicial survey that covered 3,500 criminal jury trials. In each case, the trial judge described the characteristics of the case, the jury's verdict, and how the judge would have decided the same case in a bench trial. By analyzing the case characteristics associated with agreement and disagreement between the judge and jury, Kalven and Zeisel attempted to map the determinants of jury decisions. Although properly hailed as innovative and emulated by later researchers, Kalven and Zeisel recognized the potential limits of relying on judicial reports and considered whether they had "studied the wrong thing" (p. …