Investigating mug shot commitment

Abstract

A commitment error occurs when participants search through mug shots for the perpetrator, make a selection from the mug book, and then select that same individual from a subsequent lineup, even when faced with the actual perpetrator. The present study replicated a performance decrement arising from the commitment effect. In another condition, participants were allowed to choose several foils that resembled the perpetrator from the mug book, rather than searching for a single perpetrator. No deficit arose in the ability to pick the actual perpetrator from a subsequent lineup. Following lineup decisions, participants made source judgments for all lineup members. Commitment resulted in participants not recognizing the perpetrator, which supported a memory-blending/replacement hypothesis. In contrast, witnesses who did not commit made source-monitoring errors, attributing the perpetrator to the mug shots. This study provides additional evidence that once an eyewitness has made an identification, no further identifications should be attempted because access to memory for the perpetrator is diminished. Alternative mug shot procedures may mitigate this problem.

Keywords:

• eyewitness identification
• mug shot exposure
• mug shot commitment

Acknowledgement

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not reflect the views of the National Science Foundation (NSF).

Notes

1. Although Thompson's initial identification did not come from a mug shot search, it is an example of commitment affecting subsequent memory for a perpetrator.

2. Traditional measures of source discrimination require participants to indicate if they had encountered an individual in the past using a yes/no judgement (see Johnson et al., 1993). We utilized Likert ratings to reveal degrees of familiarity (Schooler et al., 1988). Given that participants were asked to merely scan the mug shots, we were concerned that only a chosen photograph or a top contender would be remembered.

3. Each participant's ratings of the three new foils were averaged.

Additional information

Funding

This work was supported by a doctoral dissertation award from the National Science Foundation [grant number SES-0921761] awarded to CAG and SDG.