How juries, judges and other decision-makers think about evidence doesn't always match up with what the rules of evidence assume they will think. That's one focus of a new book co-authored by University of Virginia School of Law professor Barbara A. Spellman.

In "The Psychological Foundations of Evidence Law," written with Arizona State University professor Michael J. Saks, the authors explore how psychology informs evidence law and the rules of evidence used in federal courts.

"[We] ask how the rules of evidence fit with what cognitive and social psychologists understand about how people think, reason, remember and evaluate other people in order to determine whether those rules make sense," Spellman said.

Spellman said when legislatures enact general evidence rules or judges consider what jurors should hear or not hear in a particular case, they are making decisions based on psychology.

"They're acting as applied psychologists saying, 'Oh, this will be too difficult for people to make decisions with, this evidence is too complicated, this evidence is too emotional," she said. Published by New York University Press, the book can supplement a basic evidence law casebook or can be used in a subsequent course — as it will be by Spellman this spring when she teaches an advanced seminar called Evidence Law: Psychological Bases.

"There are interesting disparities between what the abstract rules of evidence are intended to do and what they do when they are applied by real people in real cases," Spellman said.

For instance, the rules about character evidence are concerned that juries and judges may be inclined to generalize behaviors. If a jury learns about a defendant's previous action, such as having committed a crime or a selfless act, they might be over-influenced by that information when considering the current trial. Much psychology research supports this assumption.

Another oft-studied topic that the book addresses is a jury's inability to disregard evidence when instructed to do so. Psychology research largely suggests that juries often choose not to disregard such evidence, rather than always being unable to do so. But psychologists have identified some situations and strategies that make jurors more likely to act and decide as if they had never heard the information in the first place.

"The overarching goal of having a fair trial inherently places the rule-makers and the deciders in the role of amateur psychologists," Spellman said. "Everyone involved needs to be thinking about what other people might be thinking. For example, judges must think about what evidence might unfairly bias jurors, and jurors must think about the witnesses' motivation and, how truthful their testimony is."

The authors address these problems from both psychological and legal perspectives in the book.

"We're trying to encourage the future of psychology research and get more psychology research into the law community," she said. "The Psychological Foundations of Evidence Law" is the second in a series of books that examines psychology and the law. The first in the series is "The Psychology of Tort Law," by Jennifer K. Robbennolt and Valerie P. Hans.

Spellman teaches courses on evidence and the intersection of psychology and law at the Law School. She earned her law degree from NYU, her doctorate in psychology from UCLA and her undergraduate degree from Wesleyan University.

Saks is the Regents' Professor of Law and Psychology and Faculty Fellow for the Center for Law, Science and Innovation at Arizona State University.

Founded in 1819, the University of Virginia School of Law is the second-oldest continuously operating law school in the nation. Consistently ranked among the top law schools, Virginia is a world-renowned training ground for distinguished lawyers and public servants, instilling in them a commitment to leadership, integrity and community service.