Unspringing the Witness Memory and Demeanor Trap: What Every Judge and Juror Needs to Know About Cognitive Psychology and Witness Credibility

52 Pages Posted: 22 Mar 2015

See all articles by Mark W. Bennett

Mark W. Bennett

U.S. District Court (Northern District of Iowa); Independent; Drake University - Law School

Date Written: January 29, 2015


The soul of America’s civil and criminal justice systems is the ability of jurors and judges to accurately determine the facts of a dispute. This invariably implicates the credibility of witnesses. In making credibility determinations, jurors and judges necessarily decide the accuracy of witnesses’ memories and the effect of the witnesses’ demeanor on their credibility.

Almost all jurisdictions’ pattern jury instructions about witness credibility explain nothing about how a witness’s memories for events and conversations work — and how startlingly fallible memories actually are. They simply instruct the jurors to consider the witness’s “memory” — with no additional guidance. Similarly, the same pattern jury instructions on demeanor seldom do more than ask jurors to speculate about a witness’s demeanor by instructing them to merely observe “the manner of the witness” while testifying. Yet, thousands of cognitive psychological studies have provided major insights into witness memory and demeanor. The resulting cognitive psychological principles that are now widely accepted as the gold standard about witness memory and demeanor are often contrary to what jurors intuitively, but wrongly, believe.

Most jurors believe that memory works like a video camera that can perfectly recall the details of past events. Rather, memory is more like a Wikipedia page where you can go in and change it, but so can others. Memories are so malleable, numerous, diverse, and innocuous post-event information alters them, at times in very dramatic ways. Memories can be distorted, contaminated, and even, with modest cues, falsely imagined, even in good faith. For example, an extremely small universe of people have highly superior autobiographical memory (HSAM). They can recall past details (like the color of the shirt they were wearing on August 1, 1995) from memory almost as well as a video camera. Yet, in one study, HSAM participants falsely remembered seeing news film clips of United Flight 93 crashing in a field in Pennsylvania on September, 11, 2001. No such film exists. Thus, no group has ever been discovered that is free from memory distortions. In one interesting study, students on a college campus were asked to either perform or imagine certain normal and bizarre actions: (1) check the Pepsi machine for change; (2) propose marriage to the Pepsi machine. Two weeks later, the students were tested and demonstrated substantial imagination inflation leading to false recognition of whether they performed or imagined the actions.

Few legal principles are more deeply embedded in American jurisprudence than the importance of demeanor evidence in deciding witness credibility. Historically, demeanor evidence is one of the premises for the need for live testimony, the hearsay rule, and the right of confrontation under the Sixth Amendment to the U.S. Constitution. Yet, cognitive psychological studies have consistently established that the typical cultural cues that jurors rely on, averting eye contact, a furrowed brow, a trembling hand, and stammering speech, for example, have little or nothing to do with a witness’s truthfulness. Also, jurors all too often wrongly assume that there is a strong correlation between a witness’s confidence and the accuracy of that witness’s testimony. Studies have determined that jurors’ perceptions of witness confidence are more important in determining credibility than the witness’s consistency or inconsistency. Another series of studies indicate that demeanor evidence predicts witness truthfulness about as accurately as a coin flip.

Once credibility determinations are made by the fact-finder, it is nearly impossible to overturn those decisions on post-trial motions or appeal. While the secrecy in which credibility determinations are made promotes the legitimacy of fact-finding, it also shrouds its countless failings. Despite years of overwhelming consensus among cognitive psychology scholars and numerous warnings from thoughtful members of the legal academy — judges have done virtually nothing to identify or begin to try and solve this serious problem. The one exception is eyewitness identification of suspects in criminal cases where several state supreme courts have relied heavily on cognitive psychological research to craft better science- based specialized jury instructions.

This article examines in detail and analyzes the often amazing and illuminating cognitive psychological research on memory and demeanor. It concludes with a Proposed Model Plain English Witness Credibility Instruction that synthesizes and incorporates much of this remarkable research.

Suggested Citation

Bennett, Mark W., Unspringing the Witness Memory and Demeanor Trap: What Every Judge and Juror Needs to Know About Cognitive Psychology and Witness Credibility (January 29, 2015). American University Law Review, 2015, Available at SSRN: https://ssrn.com/abstract=2581650

Mark W. Bennett (Contact Author)

U.S. District Court (Northern District of Iowa) ( email )

320 6th St.
Sioux City, IA 51101
United States
712-233-3909 (Phone)

Independent ( email )

Drake University - Law School ( email )

27th & Carpenter Sts.
Des Moines, IA 50311
United States

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