The Role of Diagnostic vs. Non-Diagnostic Facial Features in Eyewitness Identification

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The problem of innocent suspects being mistakenly convicted of a crime they did not commit and the parallel problem of guilty suspects being mistakenly released into society are attributable in no small part to the fallibility of eyewitness memory. A great deal of eyewitness memory research has focused on reducing false identifications of innocent suspects (thereby reducing the chances that they will be wrongly convicted). However, methods that reduce that unfortunate error often have the effect of increasing the complementary error, namely, the error of failing to identify guilty suspects. That tradeoff might be considered acceptable, but a better approach would involve reducing both errors simultaneously. To date, very little research has been conducted with that goal in mind, but it is the goal of the research proposed here. In particular, this research asks what can be done to enhance eyewitness discriminability (i.e., the ability to tell the difference between innocent and guilty suspects). To answer this question, the research is guided by a new theory of eyewitness identification: the diagnostic feature-detection hypothesis. Enhancing the discriminability of eyewitness memory procedures has significant broader impacts because it would decrease misidentifications of the innocent while at the same time increasing identifications of the guilty.This project will focus on three widely used eyewitness identification procedures: the traditional simultaneous lineup (in which 6 faces are shown to the witness simultaneously), the newer sequential lineup (in which the 6 faces are shown to the witness one at a time), and the showup procedure (in which only one face is shown to a witness for a yes/no decision). Virtually all police departments make use of the showup procedure (because it is often the only possibility in a fast-moving investigation), and nearly 30% of police departments have switched from the simultaneous lineup procedure to the sequential procedure. However, contrary to what was previously believed, recent work has found that both the showup and the sequential lineup are inferior to the simultaneous procedure (i.e., the simultaneous procedure can reduce false identifications of innocent suspects while at the same time increasing correct identifications of guilty suspects compared to the other two procedure). Given the common and likely continued use of the showup procedure and sequential lineup, this research proposes a series of experiments to investigate simple and convenient ways to enhance the diagnostic accuracy of these eyewitness identification procedures.