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6.6: References

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      In K. Spence & J. Spence (Eds.), The psychology of learning and motivation (Volume 2). New York: Academic Press.
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    11. Chase, W. G. & Simon, H.A. (1973). The mind’s eye in chess. In W. G. Chase (Ed.), Visual information processing.
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    14. Brandimonte, M. A., Hitch, G. J., & Bishop, D. V. M. (1992). Influence of short-term memory codes on visual image processing:
      Evidence from image transformation tasks. Journal of Experimental Psychology: Learing, Memory, and Cognition, 18, 157-165.
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    16. Perfect, T. J., & Askew, C. (1994). Print adverts: Not remembered but memorable. Applied Cognitive Psychology, 8, 693-703.
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      An example of the interaction between language and memory. Journal of Verbal Learning and Verbal Behavior, 13, 585-589.
    18. Hebb, D. O. (1948). Organization of behavior. New York: Wiley.

    Everyday memory - Eyewitness testimony


    Witness psychology is the study of human as an observer and reporter of events in life. It’s about how detailed and accurate we register what is happening, how well we remember what we observed, what causes us to forget and remember the mistakes, and our ability to assess the reliability and credibility of others' stories. It is the study of observation and memory for large and small events in life, from everyday trivialities to the dramatic and traumatic events that shook our lives (Magnussen, 2010)

    Basic concepts

    The eyewitness identification literature has developed a number of definitions and concepts that require explanation. Each definition and concept is described below.

    A lineup is a procedure in which a criminal suspect (or a picture of the suspect) is placed among other people (or pictures of other people) and shown to an eyewitness to see if the witness will identify the suspect as the culprit in question. The term suspect should not be confused with the term culprit. A suspect might or might not be the culprit, a suspect is suspected of being the culprit (Wells & Olson, 2003)

    Fillers are people in the lineup who are not suspects. Fillers, sometimes called foils or distractors, are known-innocent members of the lineup. Therefore, the identification of filler would not result in charges being brought against the filler. A culprit-absent lineup is one in which an innocent suspect is embedded among fillers and a culprit-present lineup is one in which a guilty suspect (culprit) is embedded among fillers. The primary literature sometimes calls these target-present and target-absent lineups (Wells & Olson, 2003).

    A simultaneous lineup is one in which all lineup members are presented to the eyewitness at once and is the most common lineup procedure in use by law enforcement. A sequential lineup, on the other hand, is one in which the witness is shown only one person at a time but with the expectation that there are several lineup members to be shown (Wells & Olson, 2003).

    A lineup’s functional size is the number of lineup members who are “viable” choices for the eyewitness. For example, if the eyewitness described the culprit as being a tall male with dark hair and the suspect is the only lineup member who is tall with dark hair, then the lineup’s functional size would be 1.0 even if there were 10 fillers. Today functional size is used generically to mean the number of lineup members who fit the eyewitness’s description of the culprit (Wells & Olson, 2003).

    Mock witnesses are people who did not actually witness the crime but are asked to pick a person from the lineup based on the eyewitness’s verbal description of the culprit. They are shown the lineup and are asked to indicate who is the offender. Mock witnesses are used to test the functional size of the lineup (Wells & Olson, 2003).

    The diagnosticity of suspect identification is the ratio of accurate identification rate with a culprit-present lineup to the inaccurate identification rate with a culprit- absent lineup. The diagnosticity of “not there” is the ratio of “not there” response rates with culprit-absent lineups to “not there” response rates with culprit-present lineups. The diagnosticity of filler identifications is the ratio of filler identification rates with culprit-absent lineups to filler identification rates with culprit-present lineups (Wells & Olson, 2003)

    Among variables that affect eyewitness identification accuracy, a system variable is one that is, or could be, under control of the criminal justice system, while an estimator variable is one that is not. Estimator variables include lighting conditions at the time of witnessing and whether the witness and culprit are of the same or of different races. System variables include instructions given to eyewitnesses prior to viewing a lineup and the functional size of a lineup. The distinction between estimator and system variables has assumed great significance in the eyewitness identification literature since it was introduced in the late 1970s . In large part, the prominence of this distinction attests to the applied nature of the eyewitness identification literature. Whereas the development of a literature on estimator variables permits some degree of post diction that might be useful for assessing the chances of mistaken identification after the fact, the development of a system variable literature permits specification of how eyewitness identification errors might be prevented in the first place (Wells & Olson, 2003).

    History and Reliability

    The criminal justice system relies heavily on eyewitness identification for investigating and prosecuting crimes. Psychology has built the only scientific literature on eyewitness identification and has warned the justice system of problems with eyewitness identification evidence. Recent DNA exoneration cases have corroborated the warnings of eyewitness identification researchers by showing that mistaken eyewitness identification was the largest single factor contributing to the conviction of innocent people (Wells & Olson, 2003).

    Psychological researchers who began programs in the 1970s, however, have consistently articulated concerns about the accuracy of eyewitness identification. Using various methodologies, such as filmed events and live staged crimes, eyewitness researchers have noted that mistaken identification rates can be surprisingly high and that eyewitnesses often express certainty when they mistakenly select someone from a lineup. Although their findings were quite compelling to the researchers themselves, it was not until the late 1990s that criminal justice personnel began taking the research seriously. This change in attitude about the psychological literature on eyewitness identification arose primarily from the development of forensic DNA tests in the 1990s (Wells & Olson, 2003). More than 100 people who were convicted prior to the advent of forensic DNA have now been exonerated by DNA tests, and more than 75% of these people were victims of mistaken eyewitness. The apparent prescience of the psychological literature regarding problems with eyewitness identification has created a rising prominence of eyewitness identification research in the criminal justice system. Because most crimes do not include DNA-rich biological traces, reliance on eyewitness identification for solving crimes has not been significantly diminished by the development of forensic DNA tests. The vast criminal justice system itself has never conducted an experiment on eyewitness identification (Wells & Olson, 2003).


    The experimental method has dominated the eyewitness literature, and most of the experiments are lab based. Lab-based experimental methods for studying eyewitness issues have strengths and weaknesses. The primary strength of experimental methods is that they are proficient at establishing cause–effect relations. This is especially important for research on system variables, because one needs to know in fact whether a particular system manipulation is expected to cause better or worse performance. In the real world, many variables can operate at the same time and in interaction with one another (Wells, Memon & Penrod, 2006)

    Multicollinearity can be quite a problem in archival/field research, because it can be very difficult to sort out which (correlated) variables are really responsible for observed effects. The control of variables that is possible in experimental research can bring clarity to causal relationships that are obscured in archival research. For example, experiments on stress during witnessing have shown, quite compellingly, that stress interferes with the ability of eyewitnesses to identify a central person in a stressful situation. However, when Yuille and Cutshall (1986) studied multiple witnesses to an actual shooting, they found that those who reported higher stress had better memories for details than did those who reported lower stress. Why the different results? In the experimental setting, stress was manipulated while other factors were held constant; in the actual shooting, those who were closer to the incident reported higher levels of stress (presumably because of their proximity) but also had a better view. Thus, in the actual case, stress and view covaried. The experimental method is not well suited to post diction with estimator variables—that is, there may be limits to generalizing from experiments to actual cases. One reason is that levels of estimator variables in experiments are fixed and not necessarily fully representative of the values observed in actual cases. In addition, it is not possible to include all interesting and plausible interactions among variables in any single experiment (or even in a modest number of experiments). Clearly, generalizations to actual cases are best undertaken on the basis of a substantial body of experimental research conducted across a wide variety of conditions and employing a wide variety of variables. Nevertheless, the literature is largely based on experiments due to a clear preference by eyewitness researchers to learn about cause and effect. Furthermore, ‘‘ground truth’’ (the actual facts of the witnessed event) is readily established in experiments, because the witnessed events are creations of the experimenters. This kind of ground truth is difficult, if not impossible, to establish when analyzing actual cases (Wells et al. 2006).


    The world is complex. All natural situations or scenes contains infinitely more physical and social information than the brain is able to detect. The brain’s ability to record information is limited. In studies of immediate memory for strings of numbers that have been read once, it turns out that most people begin to go wrong if the number of single digits exceeds five (Nordby, Raanaas & Magnussen, 2002). The limitations of what humans are capable to process, leads to an automatically selection of information. This selection is partially controlled by external factors, the factors in our environment that captures our attention (Magnussen, 2010). In the witness psychology we often talk about the weapon focus, in which eyewitnesses attend to the weapon, which reduces their memory for other information (Eysenck & Keane, 2010). The selection of information in a cognitive overload situation is also governed by psychological factors, the characteristics of the person who is observing. It is about the emotional state and the explicit and implicit expectations of what will happen. Psychologists call such expectations cognitive schemas. Cognitive schemas forms a sort of hypotheses or map of the world based on past experiences. These hypotheses or mental maps of the world determines what the brain chooses of the information, and how it interprets and if it will be remembered. When information is uncertain or ambiguous, the psychological factors are strong (Magnussen, 2010).

    Eyewitness testimony can be distorted via confirmation bias, i.e., event memory is influenced by the observer’s expectation. A study made by Lindholm and Christianson (1998), Swedish and immigrant students saw a videotaped simulated robbery in which the perpetrator seriously wounded a cashier with a knife. After watching the video, participants were shown color photographs of eight men – four Swedes and the remainder immigrants. Both Swedish and immigrant participants were twice as likely to select an innocent immigrant as an innocent swede. Immigrants are overrepresented in Swedish crime statistics, and this influenced participants’ expectations concerning the likely ethnicity of the criminal (Eysenck & Keane, 2010)

    Bartlett (1932) explained why our memory is influenced by our expectations. He argued that we possess numerous schemas or packets of knowledge stored in long-term memory. These schemas lead us to form a certain expectations and can distort our memory by causing us to reconstruct an event details based on “what must have been true”(Eysenck & Keane, 2010). What we select of information, and how we interpret information is partially controlled by cognitive schemas. Many cognitive schemas are generalized, and for a large automated and non-conscious, as the expectation that the world around us is stable and does not change spontaneously. Such generalized expectations are basic economic and making sure we do not have to devote so much energy to monitor the routine events of daily life, but they also contribute to the fact that we in certain situations may overlook important, but unexpected information, or supplement the memory with details who is form consistent, but who actually don´t exist (Magnussen, 2010).

    Estimator variables

    First, estimator variables are central to our understanding of when and why eyewitnesses are most likely to make errors. Informing police, prosecutors, judges, and juries about the conditions that can affect the accuracy of an eyewitness account is important. Second, our understanding of the importance of any given system variable is, at least at the extreme, dependent on levels of the estimator variables. Consider a case in which a victim eyewitness is abducted and held for 48 hours by an unmasked perpetrator; the witness has repeated viewings of the perpetrator, lighting is good, and so on. We have every reason to believe that this witness has a deep and lasting memory of the perpetrator’s face. Then, within hours of being released, the eyewitness views a lineup. Under these conditions, we would not expect system variables to have much impact. For instance, a lineup that is biased against an innocent suspect is not likely to lead this eyewitness to choose the innocent person, because her memory is too strong to be influenced by lineup bias. On the other hand, when an eyewitness’s memory is weaker, system variables have a stronger impact. Psychologists have investigated the effects on identification accuracy of a large number of estimator variables, witness, crime, and perpetrator characteristics. Here we recount findings concerning several variables that have received significant research attention and achieved high levels of consensus among experts (based on items represented in a survey by Kassin, Tubb, Hosch, & Memon, 2001) or have been the subject of interesting recent research (Wells et al. 2006).


    Eysenck, M.E., & Keane, M.T., (2010). Cognitive psychology. A student´s Handbook (6th Edn). New York: Psychological Press

    Magnussen, S., (2010). Vitnepsykologi. Pålitelighet og troverdighet I dagligliv og rettssal. Oslo: Abstrakt forlag as.

    Nordby, K., Raanaas, R.K. & Magnussen, S. (2002). The expanding telephone number. I: Keying briefly presented multiple-digit numbers. Behavior and Information Technology, 21, 27-38.

    Wells, G.L., Memon, A., & Penrod, S.D. ( 2006). Eyewitness Evidence. Improving Its Probative Value, 7(2), 45-75.

    Wells, G.L., & Olson, E.A., (2003). Eyewitness Testimony, 54:277-95. Doi: 10.1146/annurev.psych.54.101601.145028

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