A signal-detection-based diagnostic-feature-detection model of eyewitness identification.

Abstract

The theoretical understanding of eyewitness identifications made from a police lineup has long been guided by the distinction between absolute and relative decision strategies. In addition, the accuracy of identifications associated with different eyewitness memory procedures has long been evaluated using measures like the diagnosticity ratio (the correct identification rate divided by the false identification rate). Framed in terms of signal-detection theory, both the absolute/relative distinction and the diagnosticity ratio are mainly relevant to response bias while remaining silent about the key issue of diagnostic accuracy, or discriminability (i.e., the ability to tell the difference between innocent and guilty suspects in a lineup). Here, we propose a signal-detection-based model of eyewitness identification, one that encourages the use of (and helps to conceptualize) receiver operating characteristic (ROC) analysis to measure discriminability. Recent ROC analyses indicate that the simultaneous presentation of faces in a lineup yields higher discriminability than the presentation of faces in isolation, and we propose a diagnostic feature-detection hypothesis to account for that result. According to this hypothesis, the simultaneous presentation of faces allows the eyewitness to appreciate that certain facial features (viz., those that are shared by everyone in the lineup) are non-diagnostic of guilt. To the extent that those non-diagnostic features are discounted in favor of potentially more diagnostic features, the ability to discriminate innocent from guilty suspects will be enhanced.

Comparing the diagnostic accuracy of suspect identifications made by actual eyewitnesses from simultaneous and sequential lineups in a randomized field trial

“…A new theory about that issue was recently proposed by Wixted and Mickes (2014). The essence of their theory holds that a simultaneous lineup (but not a sequential lineup) provides immediate, diagnostically relevant information that an eyewitness can use to help identify a guilty suspect and to avoid misidentifying an innocent suspect.…”

ROC curve analyses of eyewitness identification decisions: An analysis of the recent debate

“…Precisely this sort of simulation and data-fitting process has been instrumental in development of theory in the broader literature on memory (e.g., Clark & Gronlund, 1996; Shiffrin & Steyvers, 1997), and we have every reason to believe that it offers the same advantages in the subfield of eyewitness identifications. Wixted and Mickes (2014) provided a first step in that direction; we hope that others will follow their lead.…”

“…Our simulations suggest that the most appropriate conclusion to draw from these studies is that showup identification accuracy is inferior to lineup identification accuracy. (See Wixted and Mickes [2014] for a possible theoretical explanation of that difference. )…”

From the Pigeon Lab to the Courtroom

“…Fortunately, simple theoretical principles from the perceptual learning literature very naturally explain why simultaneous lineups should be diagnostically superior to sequential lineups in terms of discriminability. The basic idea, as argued by Wixted and Mickes (2014), is that simultaneous lineups immediately teach the witness that certain facial features are nondiagnostic and therefore should not be relied upon to try to decide whether or not the guilty suspect is in the lineup. The nondiagnostic features are the features that are shared by every member of the lineup (the fillers and suspect alike, and whether the suspect is innocent or guilty).…”

“…By contrast, sequential lineups encourage a witness to choose a lineup member only if the familiarity signal exceeds an absolute decision criterion. Wixted and Mickes (2014) argued that this is a theory of response bias (i.e., simultaneous lineups engender a more liberal response bias than sequential lineups), not a theory of discriminability. In agreement with this view, Wells (1984) wrote, "It is possible to construe of the relative judgments process as one that yields a response bias, specifically a bias to choose someone from the lineup" (p. 94).…”