Eyewitness Testimony

Texas resident Larry Fuller was officially pardoned in 2007 for a rape he did not commit and for which he spent 19 years in prison—one of more than 200 erroneous convictions overturned by DNA evidence in the United States since 1989. In at least 75% of these cases, as in Fuller's, eyewitness error contributed to wrongful conviction. Partly to understand such errors, eyewitness scientists have built on 100 years of memory research in psychology to develop principles of perception and memory specific to the eyewitness experience. In the process, memory myths frequently held by both professionals and laypersons have been challenged. For example, research findings during the past three decades contradict the common belief that memories for traumatic events lie hidden in pristine and recoverable form. A more sophisticated and nuanced understanding has emerged—that any experienced event is perceived and encoded incompletely into memory and later recalled as an amalgam of true recollection and intruding non-memory elements. This entry describes issues relating to eyewitness testimony.

A police investigator might describe the perfect eyewitness as an observer who is attentive to all that transpires during a crime, who draws all meaningful crime details into memory, retains that information across time, and later recollects the crime with total accuracy. This ideal memory process—encoding, retention, and retrieval of experienced events—begins with perception. Before any information can be encoded into memory, an eyewitness's perceptual systems must be successfully deployed. Visual acuity, sharp hearing, and such properties of the senses, along with one basic requirement, namely that the witness is paying attention, will affect the quality of information available for encoding crucial details into memory. Unlike the ideal, however, actual eyewitnesses have less than perfect perception, a problem compounded by the complexities of the crime and the viewing environment (e.g., distance, illumination, visual obstructions, and perpetrator disguise). The limitations of human perception constrain the quality of resulting memory.

The eyewitness literature catalogues many perceptual difficulties for eyewitnesses, that is, factors that reduce the likelihood that useful, veridical details of a crime, including details about the perpetrator, are brought into and retained in the observer's memory. First, the eyewitness's attention to the event is crucial. The weapon focus effect exemplifies the intersection of crime context and perceptual processes. During a crime of short duration that involves a weapon, the eyewitness's attention is typically riveted on the threatening weapon that is suddenly central to his or her well-being. Later attempts to recollect peripheral details and recognize the perpetrator are less successful than for those eyewitnesses exposed to the same stimulus event without a weapon. This narrowing of visual attention can even interfere with the perception of auditory information. Also, witnesses tend to focus on action rather than persons, resulting in incomplete memory for the offender. Field demonstrations of change blindness further indicate that observers who concentrate on a central action or task fail to notice even large adjustments in the broader visual field. For example, 50% of persons who were asked by a stranger for campus directions and then unknowingly subjected to an experimental sleight-of-hand in which the stranger was surreptitiously replaced by a different person (as construction workers carried a large door between the subject and requester, temporarily blocking the subject's view of the stranger) failed to recognize the change even as they continued to provide the requested directions.

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