Eyewitness Testimony

Eyewitness testimony refers to verbal statements from people regarding what they observed and can purportedly remember that would be relevant to issues of proof at a criminal or civil trial. Such statements constitute a common form of evidence at trials. Eyewitness identification is a specific type of eyewitness testimony in which an eyewitness claims to recognize a specific person as one who committed a particular action. In cases where the eyewitness knew the suspect before the crime, issues of the reliability of memory are usually not contested. In cases where the perpetrator of the crime was a stranger to the eyewitness, however, the reliability of the identification is often at issue. Researchers in various areas of experimental psychology, especially cognitive and social psychology, have been conducting scientific studies of eyewitness testimony since the early 1900s, but most of the systematic research has occurred only since the mid- to late 1970s. There now exists a large body of published experimental research showing that eyewitness testimony evidence can be highly unreliable under certain conditions. In recent years, wrongful convictions of innocent people have been discovered through post-conviction DNA testing, and these cases show that more than 80 percent of these innocent people were convicted using mistaken eyewitness identification evidence. These DNA exoneration cases, along with previous analyses of wrongful convictions, point to mistaken eyewitness testimony as the primary cause of the conviction of innocent people.

Psychologists commonly partition memory into three distinct phases. The first phase is acquisition. The acquisition phase refers to processes involved in the initial encoding of an event and the factors that affect the encoding. Problems in acquisition include the effects of expectations, attention, lighting, distance, arousal, and related factors that control the types, amount, and accuracy of the encoded information. Eyewitnesses to crimes often witness the event under poor conditions because the event happens unexpectedly, rapidly, and/or under conditions of fear. Also, their attention may be focused on elements that are of little use for later recognition of the perpetrator, such as focusing on a weapon. The second phase is retention. Information that is acquired must be retained for later use. Memory generally declines rapidly in the initial time periods and more slowly later, in what psychologists describe as a “negatively decelerating curve.” Importantly, new information can be acquired during this phase and mixed together with what was previously observed to create confusion regarding what was actually seen by the eyewitness and what was perhaps overheard later. It is now well established through controlled experiments that witnesses will use false information, contained in misleading questions, to create what appear to be new memories that are often dramatically different from what was actually observed. The final phase is the retrieval phase. The two primary types of retrieval are recall and recognition. In a recall task, the witness is provided with some context (e.g., the time frame) and asked to provide a verbal report of what was observed. In a recognition task, the witness is shown some objects (or persons) and asked to indicate whether any of them were involved in the crime event. Retrieval failures can be either errors of omission (e.g., failing to recall some detail or failing to recognize the perpetrator) or errors of commission (e.g., recalling things that were not present or picking an innocent person from a lineup). Problems at any of the three phases of memory lead to unreliability in testimony.

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