Warnings Reduce the Sequential Lap Effect in Eyewitness Identification

Recent studies in eyewitness identification have pointed to an advantage in accuracy for witnesses to identify suspects from a sequential, rather than simultaneous, lineup. Under the sequential procedure, some witnesses may wish to see another viewing (or lap) of the lineup if they did not get a good look at the suspects during the first viewing. Should police detectives allow multiple-lap lineups? Previous research shows that identification accuracy decreases from one lap to two laps, and some detectives may want to warn witnesses of this possibility before proceeding with a second viewing. The present study tested which presentation method (one lap, two laps, or two laps with a warning) produces the highest rate of correct decisions among culprit-present and culprit-absent lineups. All participants viewed a one-minute video portraying the theft of a laptop and then completed a distracter task for five minutes. In the identification phase, one-lap participants answered whether each of six mugshots was the culprit in the video, as well as their confidence in each decision. All two-lap participants viewed the lineup once without answering and a second time while answering as the one-lap participants did. Warned two-lap participants were given a warning of the possible detriment to identification accuracy before proceeding with the second viewing. Results indicated a lap effect – two-lap participants identified fillers more often than one-lap participants regardless of culprit presence. A warning effect also emerged, but only under the culprit-absent lineup: even though two-lap participants had a higher rate of filler identifications, those who received a warning chose a filler less often than those who did not. These findings imply that witnesses should be strongly encouraged to make a decision after only one viewing, but those witnesses who absolutely require multiple viewings should be warned to take care in identifying a suspect.