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The cognitive processes of memory can be divided into three phases the encoding, the storage, and the retrieval of memory. When an individual encounters an object, a person, or an event, s/he encodes the information received from these into the cognitive system. The encoding process is influenced by a variety of factors (such as age, race, time ect) that in turn determine the accuracy of the person's memory. After encoding the information, the person stores it in one's memory until needed for future references. Several retrievals of episodes may alter and replace the original memory and thus may decrease its accuracy. This information-processing model of memory can be used for explaining and understanding the accuracy of eyewitness memory. The accuracy of eyewitness memory at the time of crime, in the encoding and storage stages, can be influenced by the characteristics of the witness, the traits of the perpetrator, and the attributes of the event of crime (Leyva, Malpass, Meissner, Pruss, Rigoni, Ross, Topp, Tredoux, & Zimmerman, 2005).
Characteristics of the witness
Such characteristics include the race, ethnicity, gender, age, occupation, confidence, intelligence, and mood of the witness and whether the witness is under the influence of alcohol and/or drugs during the crime.
To date there are no significant studies to show that a particular race, or ethnicity is more accurate in memory processes (Wells & Olson, 2003). The same can be argued for gender, in fact according to Powers, Andriks, & Loftus (1979) although males and females tend to remember different details, the level of accuracy is equal. In addition, although in 1938, Howells discovered that there is a connection between face recognition accuracy and intelligence, more recent studies such as that of Brown, Deffenbacher, and Sturgill (1977) found no link. However, this may be due to the fact that whilst, Howells experimented with low intelligence people, Brown et al. used smarter people as their sample of research. There is also no difference between the accuracy of witnesses who are law enforcement officers and those who are not professionals. However, officers tend to provide better descriptions of the crime due to the nature of their work (Leyva et al., 2005).
On the other hand the accuracy of eyewitness memory is dependent on the age of the witness. This explains why children and the elderly are less likely to remember accurate details of a crime since their memory is not proficient as that of the adults. Young children that have not yet reached their early teens have a limited memory recall and performance when compared to adults and young adults, although there is no significant difference in the proportion of correct information they recall (Leyva et al., 2005). Similarly, old people are more likely to make inaccurate identifications of suspects since they tend to have lower quantity and quality of memory recall (Searcy, Bartlett, Memon, & Swanson, 2001).
Accuracy is also subject to the confidence of the eyewitness. In fact, this is shown by studies that use the calibration method to measure the level of confidence in people, and to compare groups of people with different confidence levels to their accuracy (Brewer, Keast, & Rishworth, 2002; Brewer &Wells, 2006; Cutler & Penrod, 1989; Juslin, Olsson, & Winman, 1996; Weber & Brewer, 2003, 2004). For example Juslin et al. (1996), using such a method found out that the higher the level of confidence of a person, the higher the accuracy. However, other studies show that the relationship between these two is weak (Sporer, Penrod, Read, & Cutler, 1995).
Alcohol and drugs may also influence the accuracy of eyewitness memory, however different studies show varied results. Some research shows that the link between alcohol and accuracy is largely reliant on the intoxication levels at the time of crime, that is, the higher the level of alcohol in the blood, the lower the accuracy levels. This is mainly because alcohol (and drugs) alters the perception of people, which affect their capability to encode and store information (White, 2003). Contrarily, Yuille, Tollestrup, Marxsen, Porter, & Herve (1998) found out that drugs like marijuana have very little influence on memory recall accuracy and effect memory storage only temporarily.
The mood of the witness may also determine the level of accuracy of the memory of crime. Having a negative mood may improve memory processes, since when a person is in a bad mood, s/he is more likely to be alert than when in a good mood (Schwartz & Bless, 1991, as cited in Forgas, Laham, and Vargas, 2005). Moreover, it could also be due to the fact that cognitive effort is higher when trying to repair negative moods, then when trying to maintain a good mood (Clark & Isen, 1982). On the other hand, Forgas, Laham, and Vargas (2004) argue that people in a negative mood are more prone to false alarms.
Attributes of the event of crime
The characteristics of the event itself can influence the accuracy of the memory of the eyewitness. Such factors include the duration of exposure to the event, the viewing distance and the visibility between the perpetrator and the witness, the lighting conditions of the place, the stress and fear suffered by the witness during the crime, focussing on the weapon, and the knowledge that one is witnessing a crime (Leyva et al., 2005).
The longer one is exposed to the crime situation, the higher is the possibility of remembering clearly and accurately the event. However, an optimal viewing time that identifies the needed time to remember something accurately, does not exist, since it highly depends on the person and his/her attention and interest in the incident (Leyva et al., 2005). The attention highly depends on how long the eyewitness takes to realise that s/he is witnessing a crime (Wells & Olson, 2003). In fact according to Leippe, Wells, & Ostrom (1978), many witnesses realise they have witnessed a crime after the offender flees the crime scene, even though they sometimes view the culprit for a significant amount of time.
Weapon focus can lead to another factor that can affect the accuracy of memory: stress and arousal. In fact, the presence of weapons can cause a person witnessing a crime to become stressed, and full of arousal and fear, and this results in a narrowing of attention with a loss of marginal details (Christianson, 1992). Whilst some studies show that high levels of violence increase the chance of stress and arousal (Clifford & Hollin, 1981), other studies found no link between these (Cutler, Penrod, & Martens, 1987b). Perhaps the most significant study on this matter is that of Deffenbacher (1983), which came up with the Yerkes-Dodson Law. This law tries to explain how an increase in arousal improves performance up to a certain optimum point, when this critical point is passed, memory performance decreases (McLeod, 2009).Â
Another factor that influences the attention of the eyewitness is whether a weapon is used in the crime or not. Studies show that when a weapon is used in the commission of a crime, the witnesses tend to focus their attention on the weapon and thus do not take as much notice of other important details such as the face of the perpetrator and the characteristics of the crime (Steblay, 1992; Brain, 2002). This is mostly done because the witnesses may be afraid that the weapon will be used against them, and thus at the time of crime it is perceived as the main threat. This effect of weapon focus does not only occur when the witness is the victim, but also when the witness is not under direct threat from the weapon (Leyva et al., 2005).
Accuracy of memory storage and encoding depends on the viewing distance and visibility of the witness. Visibility improves as the viewing distance decreases, and with good lighting and weather conditions (Wells & Olson, 2003). Consequently, during the morning and in an illuminated place, the witness is able to view the crime event better and more clearly and thus increase the amount of information available for encoding. However, one important point to keep in mind is that there are no reliable estimates of lighting and viewing distances that can be used as a basis for assessing the accuracy of the eyewitness (Leyva et al., 2005).
Traits of the perpetrator
Besides being affected by characteristics of the eyewitness her/himself, and by the attributes of the crime event, memory accuracy can also depend on perpetrators' traits. Such traits involve disguises used by the culprit, whether the offender has a distinctive feature that can easily be remembered, whether the race and gender of the perpetrator are similar to those of the witness, and familiarity between the eyewitness and the suspect (Leyva et al., 2005).
It is quite common for people to make use of disguises when engaging in criminal acts. This makes it easier for the offender to get away from the crime scene without being identified. On the other hand, disguises make it more difficult for the eyewitnesses to memorise features of the criminal (Cutler, Penrod, & Martens, 1987a, 1987b; McKelvie, 1988; Patterson & Baddeley, 1977). Disguises may include full-face masks, stockings, hats, sunglasses and hoods: all used to cover the hair and hairline of the perpetrator. In fact studies show that the "upper regions of the face, [head shape, hairline, eyes, eyebrows, and nose] tend to contribute to successful recognition" (Leyva et al., 2005, pp. 4).
Although wearing disguises decreases the possibility of the identification of the culprit, certain distinctive features of the offender that are easily noticed and memorised, can help in recognising the perpetrator in the future. In fact, it is more difficult to identify "typical" facial features, than for example faces with a protruding chin or birthmark (Leyva et al., 2005). Furthermore, tattoos and body piercings may also be useful to help the eyewitness memorise and later identify the culprit more accurately (Wells & Olson, 2003). Highly attractive or unattractive people are also easier to memorise than average looking persons (Fleishman, Buckley, Klosinsky, Smith, & Tuck, 1976).
Evidence shows that people tend to recognise faces of their own race or ethnicity rather than those of other races/ ethnicities. This is better known as the "Cross Race Effect," the "Own Race Bias" or the "Other-Race Effect" (Michel, Rossion, Han, Chung, & Caldara, 2006). However, there is no evidence that shows that any particular ethnicity or race is able to accurately identify another racial or ethnic group, although exposure to such other "groups" may improve the identification (Leyva et al., 2005). This maybe explains why people find it easier to memorise other persons of their own race/ethnicity. According to Leyva et al. (2005, pp. 5), familiarity plays a strong role in the recognition of faces." In fact, it is easier to remember a person that one knows that one who is a complete stranger.
All estimator variables (attributes of the witness, event, and perpetrator) that are present at the time of crime may all influence the accuracy of eyewitness memory. As explained by various studies eyewitness memory is highly dependent on the age, occupation, confidence, intelligence, and mood of the witness. Moreover, being under the influence of drugs and/or alcohol may also effect perception and as a result the amount of accurate detail about the crime event that is encoded by the witness. The conditions of the crimes such as the duration of exposure to the event, the viewing distance between the perpetrator and the witness, the lighting conditions of the place, the stress and fear suffered by the witness during the crime, may all affect memory accuracy. Besides this disguises and weapons used by the culprit and when the race of the perpetrator is different to that of the witness, memory accuracy is likely to decrease. On the other hand, when the offender has a distinctive feature that can easily be remembered, and familiarity between the eyewitness and the suspect can all facilitate memory encoding as storage (Leyva et al., 2005).