Witnesses’ memories for lineup fillers postdicts their identification accuracy

Witnesses who have quick, automatic recognition experiences when viewing a lineup tend to make more accurate decisions than witnesses who engage in slower, more deliberative processes. A novel postdictor of identification accuracy is predicted from these findings: memories for lineup fillers should be stronger among inaccurate, rather than accurate, witnesses. Undergraduate students (N = 320) viewed a mock crime, made a lineup identification decision, and were given a surprise test for their memory for the lineup fillers. Consistent with predictions, better memories for lineup fillers postdicted mistaken identifications and the suspect's innocence. Information gain analyses showed that under some conditions, memory for lineup fillers provided as much information about the suspect's guilt as a lineup identification. Findings are consistent with the idea that postdictors of eyewitness accuracy are valuable to the extent that they measure the automaticity or deliberativeness of the witness's experience when viewing the lineup.

► A novel postdictor of eyewitness accuracy is tested: memory for lineup fillers.
► Accurate witnesses remembered fewer lineup fillers than inaccurate witnesses.
► Good memory for fillers suggests that the witness failed to recognize the suspect.
► A witness's memory for fillers provides information about the suspect's guilt.