The Problem with Eyewitness Testimony
a talk by
George Fisher, Professor of Law
Stanford Law School, April 5, 1999. In a presentation
sponsored by the Stanford Journal of Legal Studies, George
Fisher placed Barbara Tverskys research on memory fallibility into the context of
police investigations and jury verdicts, discussing the relevance of such research to our
system of justice.
Several studies have been conducted on human memory and on subjects propensity to remember erroneously events and details that did not occur. Elizabeth Loftus performed experiments in the mid-seventies demonstrating the effect of a third partys introducing false facts into memory.4 Subjects were shown a slide of a car at an intersection with either a yield sign or a stop sign. Experimenters asked participants questions, falsely introducing the term "stop sign" into the question instead of referring to the yield sign participants had actually seen. Similarly, experimenters falsely substituted the term "yield sign" in questions directed to participants who had actually seen the stop sign slide. The results indicated that subjects remembered seeing the false image. In the initial part of the experiment, subjects also viewed a slide showing a car accident. Some subjects were later asked how fast the cars were traveling when they "hit" each other, others were asked how fast the cars were traveling when they "smashed" into each other. Those subjects questioned using the word "smashed" were more likely to report having seen broken glass in the original slide. The introduction of false cues altered participants memories.
Courts, lawyers and police officers are now aware of the ability of third parties to introduce false memories to witnesses.5 For this reason, lawyers closely question witnesses regarding the accuracy of their memories and about any possible "assistance" from others in the formation of their present memories. However, psychologists have long recognized that gap filling and reliance on assumptions are necessary to function in our society. For example, if we did not assume that mail will be delivered, or that the supermarkets will continue to stock bread, we would behave quite differently than we do. We are constantly filling in the gaps in our recollection and interpreting things we hear. For instance, while on the subway we might hear garbled words like "next," "transfer," and "train." Building on our assumptions and knowledge, we may put together the actual statement: "Next stop 53rd Street, transfer available to the E train." Indeed, we may even remember having heard the full statement.
So what is an "original memory?"6 The process of interpretation occurs at the very formation of memorythus introducing distortion from the beginning. Furthermore, witnesses can distort their own memories without the help of examiners, police officers or lawyers. Rarely do we tell a story or recount events without a purpose. Every act of telling and retelling is tailored to a particular listener; we would not expect someone to listen to every detail of our morning commute, so we edit out extraneous material. The act of telling a story adds another layer of distortion, which in turn affects the underlying memory of the event. This is why a fish story, which grows with each retelling, can eventually lead the teller to believe it.
Once witnesses state facts in a particular way or identify a particular person as the perpetrator, they are unwilling or even unabledue to the reconstruction of their memoryto reconsider their initial understanding. When a witness identifies a person in a line-up, he is likely to identify that same person in later line-ups, even when the person identified is not the perpetrator. Although juries and decision-makers place great reliance on eyewitness identification, they are often unaware of the danger of false memories.
Experiments conducted by Barbara Tversky and Elizabeth Marsh corroborate the vulnerability of human memory to bias.7 In one group of studies, participants were given the "Roommate Story," a description of incidents involving his or her two fictitious roommates. The incidents were categorized as annoying, neutral, or socially "cool." Later, participants were asked to neutrally recount the incidents with one roommate, to write a letter of recommendation for one roommates application to a fraternity or sorority, or to write a letter to the office of student housing requesting the removal of one of the roommates. When later asked to recount the original story, participants who had written biased letters recalled more of the annoying or "cool" incidents associated with their letters. They also included more elaborations consistent with their bias. These participants made judgements based upon the annoying or social events they discussed in their letters. Neutral participants made few elaborations, and they also made fewer errors in their retelling, such as attributing events to the wrong roommate. The study also showed that participants writing biased letters recalled more biased information for the character they wrote about, whereas the other roommate was viewed neutrally.
Memory is affected by retelling, and we rarely tell a story in a neutral fashion. By tailoring our stories to our listeners, our bias distorts the very formation of memoryeven without the introduction of misinformation by a third party. The protections of the judicial system against prosecutors and police "assisting" a witness memory may not sufficiently ensure the accuracy of those memories. Even though prosecutors refrain from "refreshing" witness As memory by showing her witness Bs testimony, the mere act of telling prosecutors what happened may bias and distort the witnesss memory. Eyewitness testimony, then, is innately suspect.
Lawyers place great import on testimony by the other sides witness that favors their own sides case. For example, defense attorneys make much of prosecution witnesses recollection of exonerating details. In light of psychological studies demonstrating the effect of bias on memory, the reliance and weight placed on such "admissions" may be appropriate, since witnesses are more apt to tailor their storiesand thus their memoriesto the interests of the first listeners. An eyewitness to a crime is more inclined to recount, and thus remember incriminating details, when speaking to a police officer intent on solving the crime. If later the eyewitness still remembers details that throw doubt on the culpability of the suspect, such doubts should hold greater weight than the remembrance of incriminating details.
In another part of the Tversky-Marsh study, participants were asked to play prosecutors presenting a summation to the jury.8 Participants first read a murder story, where two men were suspects. Participants were then asked either to prepare a neutral recounting of all they remembered about one suspect, or to prepare a summation to the jury about one suspect. Later, participants were asked to recall the original story. Participants who wrote summations recalled more incriminating details and wrongly attributed details among suspects more often than participants who originally wrote a neutral recounting.
Bias creeps into memory without our knowledge, without our awareness. While confidence and accuracy are generally correlated, when misleading information is given, witness confidence is often higher for the incorrect information than for the correct information. This leads many to question the competence of the average person to determine credibility issues. Juries are the fact-finders, and credibility issues are to be determined by juries. The issue then arises whether juries are equipped to make these determinations. Expert testimony may not be helpful. Indeed, since the very act of forming a memory creates distortion, how can anyone uncover the "truth" behind a persons statements? Perhaps it is the terrible truth that in many cases we are simply not capable of determining what happened, yet are duty-bound to so determine. Maybe this is why we cling to the sanctity of the jury and the secrecy of jury findings:
The courts reliance on witnesses is built into the common-law judicial system, a reliance that is placed in check by the opposing counsels right to cross-examinationan important component of the adversarial legal processand the laws trust of the jurys common sense. The fixation on witnesses reflects the weight given to personal testimony. As shown by recent studies, this weight must be balanced by an awareness that it is not necessary for a witness to lie or be coaxed by prosecutorial error to inaccurately state the factsthe mere fault of being human results in distorted memory and inaccurate testimony.