Why are lineups better than showups? A test of the filler siphoning and enhanced discriminability accounts.

Abstract

Presenting the police suspect alongside similar-looking people (a lineup) results in more accurate eyewitness identification decisions than presenting the suspect alone (a showup). Why are lineups better than showups? Diagnostic-feature-detection theory suggests that lineups enhance witnesses’ ability to discriminate between innocent and guilty suspects, because facial features can be compared across lineup members. Filler-siphoning suggests that the presence of other lineup members siphons some of the incorrect identifications that would otherwise land on the innocent suspect. To test these 2 accounts, over 3,600 subjects across 3 experiments watched a mock-crime video and were presented with either a showup, a simultaneous lineup, or a simultaneous showup (a novel procedure). Subjects in the simultaneous showup condition saw the suspect and 5 similar-looking faces, but, unlike a lineup, could not identify the other faces. Presenting similar-looking faces alongside the suspect (simultaneous showup and lineup) enhanced subjects’ ability to discriminate between innocent and guilty suspects compared with presenting the suspect alone (showup) as measured by Area Under the ROC Curve (pAUC) and fitting a signal-detection model. These results show, for the first time, that the discriminability advantage in simultaneous lineups is because of the comparison of multiple faces as predicted by diagnostic-feature-detection theory, but not the filler-siphoning account.

The number of fillers may not matter as long as they all match the description: The effect of simultaneous lineup size on eyewitness identification

“…This strong CA relationship has held up well across levels of both estimator (e.g., Carlson et al, ; Carlson & Carlson, ; Dodson & Dobolyi, ; Palmer, Brewer, Weber, & Nagesh, ) and system variables (e.g., Mickes, ; Seale‐Carlisle & Mickes, ; Wixted & Wells, ). However, one exception is the showup, which produces a worse CA relationship compared to lineups (e.g., Colloff & Wixted, ; Key et al, ; Mickes, ). We therefore expected that our showups would yield a worse CA relationship compared to all lineup sizes.…”

“…Rather than involving empirical discriminability, DFS is a theory of response bias concerning differences in whether a filler, a suspect, or neither are chosen (Colloff, Wade, Strange, & Wixted, ; Rotello & Chen, ; Wetmore, McAdoo, Gronlund, & Neuschatz, ). Moreover, evidence that filler siphoning affects discriminability has not been borne out by recent research (Colloff & Wixted, ; Rotello & Chen, ; Wetmore et al, ). Based in part on these reasons, our primary focus is testing an extension of the DFD hypothesis, which has more explicit predictions concerning empirical discriminability.…”

“…When the actual person who committed the crime is the suspect then it is a target‐present (TP) lineup and if he is not present then it is a target‐absent (TA) lineup. While a general consensus exists for the superiority of the simultaneous lineup over a one‐person identification (ID) procedure (i.e., a showup; Colloff & Wixted, ; Gronlund et al, ; Wetmore et al, ) and there is mounting evidence that it is more beneficial than presenting members sequentially (Carlson & Carlson, ; Dobolyi & Dodson, ; Gronlund et al, ; Mickes, Flowe, & Wixted, ; Seale‐Carlisle, Wetmore, Flowe, & Mickes, ), there has been less research concerning what the optimal nominal size of a lineup should be (Clark, Moreland, & Rush, ). Currently, it is unclear exactly how many fillers should be included to maximize eyewitness accuracy.…”

“…This, in turn, allows the eyewitness to focus their attention on the features most diagnostic of suspect guilt (i.e., features not shared by all lineup members). Although most of the empirical comparisons have been made between six‐member simultaneous lineups and showups (Colloff & Wixted, ; Gronlund et al, ; Key et al, ; Mickes, ; Wetmore et al, ), the same logic should apply to a lineup composed of fewer members. That is, adding very few high‐quality fillers (i.e., those that all have the description‐matched features mentioned by the eyewitness) should theoretically allow an eyewitness to discount these shared, and therefore non‐diagnostic, features (e.g., age, hair color, race), thereby helping the witness to focus on more non‐overlapping, diagnostic features (e.g., shape of nose and eyes).…”

“…One goal of our study is to determine if the pattern holds across simultaneous lineups of various sizes. For showups, there has been evidence to suggest that even for IDs made with higher confidence, the CA relationship is weaker compared to lineups (e.g., Colloff & Wixted, ; Key et al, ; Mickes, ). We sought to determine whether an ID coming from a 3‐member lineup can be just as trustworthy as a larger lineup and how each of these procedures compares to showups.…”