Debate the reliability of eyewitness testimony in court from the perspective of what cognitive psychology tells us about the human memory system.

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Debate the reliability of eyewitness testimony in court from the perspective of what cognitive psychology tells us about the human memory system


Eyewitness testimony is an area of cognitive psychology into which considerable research has been conducted, much of which suggests it is unreliable.  The main concerns in relation to reliability relate to what is known about the human memory system.  Specifically, research indicates that memory is selective, and that stress and high levels of arousal may impair the ability to encode and retrieve information (Clifford & Hollin, 1981; E. F. Loftus & Burns, 1982).  There is also evidence to suggest that memory is constructive, and therefore our memory of specific events may be affected by prior knowledge and expectations (List, 1986; Brewer & Treyens, 1981).  In addition to prior information, research indicates that memory can also be distorted by information we receive after an incident has taken place (Loftus, 1979).  This essay debates the reliability of eyewitness testimony in court from the perspective of what cognitive psychology tells us about the human memory system.  The essay begins by discussing the impact of stress and high levels of arousal on recall of eyewitnesses.  It then reviews evidence suggesting that memory is constructive and that schemas and scripts may lead us to make inferences about situations.  Finally, the essay evaluates the theory that post-event information may distort memory.

A large body of research (Barton & Warren, 1988; Clifford & Hollin, 1981; Clifford & Scott, 1978; E.F. Loftus & Burns, 1982) suggests that stress may be detrimental to memory, and therefore that memory for the details of unpleasant, stressful events may be less accurate than our memory for the details of neutral events.  In a survey on the reliability of eyewitness testimony, Kassin, Ellsworth & Smith (1989) reported that 79% of eyewitness testimony experts agreed that “very high levels of stress impair the accuracy of eyewitness testimony”, and 97% agreed that “eyewitnesses have greater difficulty recalling violent events than they do non-violent events”.  The basic assumption underlying these statements is that increased levels of emotional arousal decrease the amount of processing capacity available for attention and memory in accordance with the Yerkes-Dodson (1908) law.  

Much of the evidence to support this notion derives from laboratory studies into the effects on memory of viewing a violent incident.  Clifford and Hollin (1981), for example, found that participants who watched a video of a mugging gave a less accurate description of the main perpetrator than did participants who watched a video of a man asking for directions.  Furthermore, the accuracy of recall in the violent condition decreased as the number of perpetrators increased, though photographic identification of the main character was not significantly different between conditions.  Similarly, E.F. Loftus and Burns (1982) demonstrated that participants who watched a short film of a bank robbery showing a young boy being shot in the face showed poorer retention of the details of the film than did participants who saw a non-violent version of the same film.  Specifically, participants in the violent condition were less able to recall items occurring almost 2 minutes prior to the main incident.  Loftus and Burns (1982) concluded that exposure to mentally shocking events may cause retrograde amnesia for events that occur a short time prior to the event.  However, they also suggest that memory for other aspects of the violent event may be better consolidated or reinforced as a result, and could perhaps account for the poorer retention of other details (e.g., the number on the boy’s football jersey).  These findings suggest that witnessing violence may impair memory for certain peripheral aspects of the incident, though perhaps not for the main event itself.

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In particular, in cases where weapons are involved, fear and anxiety induced by the sight of the weapon may cause witnesses to allocate almost all of their attentional resources to the threatening object, leaving only limited resources to encode other details, such as details about the main perpetrator (Cutler, Penrod & Martens, 1987; Kramer, Buckhout & Eugenio, 1990; E.F. Loftus, Loftus & Messo, 1987; Maass & Koehnken, 1989; Tooley, Brigham, Maass & Bothwell, 1987).  This phenomenon is known as ‘weapon focus’.  G.R. Loftus and Mackworth (1978) showed that people fixate faster, more often and for longer durations on weapons ...

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