Researchers have argued that simultaneous lineups should follow the principle of propitious heterogeneity, based on the idea that if the fillers are too similar to the perpetrator even an eyewitness with a good memory could fail to correctly identify him. A similar prediction can be derived from the diagnostic feature-detection (DFD) hypothesis, such that discriminability will decrease if too few features are present that can distinguish between innocent and guilty suspects. Our first experiment tested these predictions by controlling similarity with artificial faces, and our second experiment utilized a more ecologically valid eyewitness identification paradigm. Our results support propitious heterogeneity and the DFD hypothesis by showing that: 1) as the facial features in lineups become increasingly homogenous, empirical discriminability decreases; and 2) lineups with description-matched fillers generally yield higher empirical discriminability than those with suspect-matched fillers.
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The diagnostic feature-detection theory (DFT) of eyewitness identification is based on facial information that is diagnostic versus non-diagnostic of suspect guilt. It primarily has been tested by discounting non-diagnostic information at retrieval, typically by surrounding a single suspect showup with good fillers to create a lineup. We tested additional DFT predictions by manipulating the presence of facial information (i.e., the exterior region of the face) at both encoding and retrieval with a large between-subjects factorial design (N = 19,414). In support of DFT and in replication of the literature, lineups yielded higher discriminability than showups. In support of encoding specificity, conditions that matched information between encoding and retrieval were generally superior to mismatch conditions. More importantly, we supported several DFT and encoding specificity predictions not previously tested, including that (a) adding non-diagnostic information will reduce discriminability for showups more so than lineups, and (b) removing diagnostic information will lower discriminability for both showups and lineups. These results have implications for police deciding whether to conduct a showup or a lineup, and when dealing with partially disguised perpetrators (e.g., wearing a hoodie).
SummaryFew studies have investigated eyewitnesses' ability to predict their later lineup performance, known as predecision confidence. We applied calibration analysis in two experiments comparing predecision confidence (immediately after encoding but prior to a lineup) to postdecision confidence (immediately after a lineup) to determine which produces a superior relationship with lineup decision accuracy. Experiment 1 (N = 177) featured a multiple‐block lineup recognition paradigm featuring several targets and lineups; Experiment 2 featured an eyewitness identification paradigm with a mock‐crime video and a single lineup for each participant (N = 855). Across both experiments, postdecision confidence discriminated well between correct and incorrect lineup decisions, but predecision confidence was a poor predictor of accuracy. Moreover, simply asking for predecision confidence weakened the postdecision confidence–accuracy relationship. This implies that police should exercise caution when interviewing eyewitnesses, as they should not be asked to predict their ability to make an accurate lineup decision.
SummaryIt is important to consider the two parameters of signal detection theory, discriminability and response bias, when evaluating eyewitness identification from simultaneous lineups. On the basis of the diagnostic feature‐detection hypothesis, we tested a method for increasing discriminability that encourages eyewitnesses to carefully rank each lineup member based on match to their memory for a perpetrator. This procedure increased empirical discriminability and also eliminated a response bias that is largely overlooked in the literature: Participants were biased to choose from the top row of the six‐pack (2 × 3) lineup commonly used in the United States. We argue that suspect position in the simultaneous lineup is an important variable to consider for researchers and the criminal justice system. We also encourage researchers to test the ranking procedure to determine if such a simple set of instructions could be utilized by police to help eyewitnesses correctly sort innocent versus guilty suspects.
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