Would you recognize the perpetrator? What do you need to know when you have to make an identification from a lineup?

For a better understanding of the psychology of lineups, it is beneficial to take a look at the different possible lineup outcomes (see Figure 1). The suspect in the lineup can be identical with the perpetrator, or non-identical with the perpetrator (i.e., an innocent suspect). Moreover, when making a lineup decision, the witness has the option to choose someone from the lineup or to reject the lineup. According to signal-detection theory, this results in four different decision outcomes (Swets, Dawes, & Monahan, 2000). First, a true positive outcome occurs if the perpetrator is present in the lineup and the witness correctly identifies him/her. This is also called a hit. Second, a true negative outcome occurs if the perpetrator is not in the lineup and the witness rejects the lineup (correct rejection). Third, a false positive outcome occurs if the perpetrator is absent in the lineup, yet the witness identifies someone. This could be the wrongful identification of a foil (foil identification) or an innocent suspect (false alarm). Whereas the former is a known error, the latter describes a fatal error that can result in a wrongful conviction. Fourth, a false negative outcome occurs if the perpetrator is present in the lineup, but the witness rejects the lineup (incorrect rejection). Finally, the witness also has the option to refrain from making a decision (“don’t know” answer).

It is straightforward that witnesses’ identification decisions depend on cognitive factors, such as the memory strength regarding the perpetrator. A less intuitive cognitive factor may be the context in which the suspect is put in the recognition situation; that is, the manner in which the lineup is presented. Furthermore, social and meta-cognitive influences also play an important role (Brewer, Weber, & Semmler, 2007). Social influences include expectancy effects identified through Robert Rosenthal’s (1966, 2002) research on the effect of teachers' expectations on schools students. Meta-cognitive variables concern our intuitive theories of how memory works (e.g., “If I’m highly confident, I should be correct”; Winkielman & Schwarz, 2001). In the next section we discuss social, cognitive and meta-cognitive variables that can influence witnesses’ decision making during the identification procedure.

Social Influences

Lineup administration--double-blind testing

While a lineup is presented, neither the witness nor the lineup administrator should be aware of the suspect's identity--a technique known as double-blind. This helps to guard against the experimenter effect (Rosenthal, 1966, 2002), a well-known phenomenon in social psychology in which the experimenter's expectations drive participants' behaviors. Transferred to eyewitness identification, the experimenter effect can cause the lineup administrator to give the witness – consciously or unconsciously - verbal and nonverbal cues about the identity of the suspect (Quinlivan, Neuschatz, Cutler, Wells, McClung, & Harker, in press). This can lead to an increase in false alarms (Phillips, McAuliff, & Cutler, 1999) without witnesses being aware of the impact the administrator has on their decisions (Greathouse & Kovera, 2008).

However, a police officer blind to the identity of the suspect cannot exert such influence. For real-world cases, this means that the investigating police officer must not administer the lineup.

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