Eyewitness Identification: Psychological Aspects

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 and rapidly. 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 slower 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. Loftus's well-known experiments on misinformation, for example, show 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. 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.