Police lineups in which distinctive individual marks or features are not altered can impair witnesses’ ability to distinguish between innocent and guilty suspects, according to new research in Psychological Science, a journal of the Association for Psychological Science.
The research, conducted by a team of psychology researchers from the University of Warwick in the UK, builds on existing eyewitness identification studies suggesting that so-called “unfair lineups,” in which the police suspect stands out, make witnesses more willing to identify that suspect.
“Worse still, it could impair their ability to distinguish between guilty and innocent suspects and distort their ability to judge the trustworthiness of their identification decision,” says Melissa Colloff, lead author on the study.
In contrast to film and TV depictions in which a witness views a police lineup via a one-way mirror, lineups today typically involve the witness looking at and evaluating digital photos. Using digital images gives the police the ability to disguise distinguishing features.
Colloff and colleagues examined the three methods currently used by English police forces to manipulate digital images in order to counteract the effect of any distinguishing marks such as black eyes, eyeglasses, and beards. In an online experiment with almost 9,000 participants, the researchers compared the three techniques – pixelating part of the face, hiding part of the face, or manipulating the photos so they contain the same feature (e.g., adding a beard) – with digital lineups that were not manipulated.
Participants watched a brief video of a crime and were told to pay attention as they would be asked questions about it later. Afterward, they completed several distractor tasks that were unrelated to the study. They were then presented with a lineup composed of two rows of three photos and were told that the culprit may or may not be present in the lineup.
The participants were …