Cognitive Cleansing: Experimental Psychology and the Exclusionary Rule

Abstract

The exclusionary rule generally bars the use of illegally obtained evidence in a criminal case, regardless of the defendant’s crime. However, using a combination of doctrinal analysis, social psychology theory, and original experimental data, this Article proposes a more cognitively complicated picture of how the rule may actually operate. In cases of egregious crime that people are highly motivated to punish, the exclusionary rule and its continually expanding exceptions present a fertile entry point for “motivated cognition,” a psychological process through which decision makers unknowingly reason toward their desired outcomes, seemingly within the constraints of the law.

In this series of experiments, when research participants acting as judges were faced with pivotal but illegally obtained evidence of a morally repugnant crime, they unknowingly construed the circumstances of the case in a manner that enabled them to invoke an exception to the exclusionary rule — thereby “cognitively cleansing” the tainted evidence to admit it and achieve their punishment goals without flouting the law. By contrast, when an identical illegal search uncovered evidence of a less reprehensible crime, participants were significantly more likely to suppress the evidence, construing the circumstances of the case to support the use of the exclusionary rule without exception. Even people’s judgments about the investigating police officers, who conducted exactly the same illegal search in both scenarios, depended on the egregiousness of the crime that the search happened to uncover. Critically, however, introducing awareness-generating instructions that alerted participants to the possibility that criminal egregiousness could drive their suppression judgments significantly curtailed the influence of this doctrinally irrelevant factor.

Contributing to a growing body of empirical research on cognitive pitfalls in legal decision making, the results of these studies highlight why the justice system should not turn a blind eye to covertly motivated applications of the exclusionary rule, or any legal doctrine that is susceptible to the motivated cognition effect. Aside from the benefits of stability and legitimacy that arise from applying legal rules in a predictable and transparent manner, the finding that decision makers set aside their personal punishment goals to more objectively adhere to the law when an instructional intervention cognitively equipped them to do so reflects a conscious choice worth recognizing. Illustrating how the tools of social psychology can be mobilized to reveal new normative dimensions of longstanding doctrinal debates and stimulate data-driven prescriptions for reform, this Article proposes a path toward more informed, consistent, and cognitively realistic applications of the law.

Keywords: exclusionary rule, law and psychology, legal decision making, experimental psychology, criminal justice, criminal procedure, Fourth Amendment, motivated cognition, motivated reasoning, inevitable discovery

JEL Classification: C90, C91, K10, K14, K40