The Problem with Eyewitness Testimony

a talk by

Barbara Tversky, Professor of Psychology


George Fisher, Professor of Law

Laura Engelhardt 

  Stanford Law School, April 5, 1999. In a presentation sponsored by the Stanford Journal of Legal Studies, George Fisher placed Barbara Tversky’s research on memory fallibility into the context of police investigations and jury verdicts, discussing the relevance of such research to our system of justice.

   The bedrock of the American judicial process is the honesty of witnesses in trial. Eyewitness testimony can make a deep impression on a jury, which is often exclusively assigned the role of sorting out credibility issues and making judgments about the truth of witness statements.1 Perjury is a crime, because lying under oath can subvert the integrity of a trial and the legitimacy of the judicial system. However, perjury is defined as knowingly making a false statement—merely misremembering is not a crime.2 Moreover, the jury makes its determinations of witness credibility and veracity in secret, without revealing the reason for its final judgement.3 Recognizing the fallibility of witness memories, then, is especially important to participants in the judicial process, since many trials revolve around factual determinations of whom to believe. Rarely will a factual question result in a successful appeal—effectively giving many parties only one chance at justice. Arriving at a just result and a correct determination of truth is difficult enough without the added possibility that witnesses themselves may not be aware of inaccuracies in their testimony.

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 party’s 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.