How many faces can we remember? Why this matters when assessing eyewitnesses

Most research on eyewitness memory has focused on single-perpetrator crimes. However, crimes to which eyewitnesses may bear testimony are often committed by groups of perpetrators. A consequence of researching only single-perpetrator crimes is that we know very little about how set size (i.e., the number of faces) at encoding impacts recognition performance. We do not know much more about this question in the face recognition literature either but the small extant literature does appear to converge on one conclusion, namely that recognition performance is worse for larger set sizes. In the case of eyewitness memory, the presence of multiple perpetrators poses an additional unique question: Eyewitnesses not only need to identify perpetrators, but also need to testify to the perpetrators' actions. Few researchers have investigated this second aspect. In this chapter, we review literature in the areas of face recognition and eyewitness memory to shed light on these questions, and present two laboratory studies that test the effects of set size on face and person recognition. Results show that recognition performance decreases as a function of set size, but that this is differentially true for faces and roles, and is in fact dramatically reduced when faces and roles are paired. There are serious applied implications for this latter finding in particular