Is developmental prosopagnosia best characterised as an apperceptive or mnemonic condition?

Traditionally, developmental prosopagnosia (DP) has been thought of as an apperceptive condition that hinders individuals' ability to encode face structure. However, several authors have recently raised the possibility that many DPs may be able to form accurate percepts, but be unable to maintain those percepts over time. The present study sought to distinguish these possibilities. In our first experiment 16 DPs and 22 typical controls completed a delayed match-to-sample task with face and car stimuli, with a retention interval of 1-second (low demand) or 6-seconds (high demand). As expected, the participants with DP were worse than the controls at face matching, and were disproportionately impaired at matching faces relative to cars. However, the relative degree of impairment seen in the DPs did not interact with retention interval; they exhibited similar levels of impairment when matching faces with 1- and 6-second delays. Next, we compared the performance of 72 DPs and 54 typical controls on the Cambridge Face Perception Test (CFPT), a task that measures face perception ability in a way that minimises the memory demands. As expected, we found that the DPs were impaired at the group level. This difference was not attributable to a few individuals with an apperceptive profile; rather we found evidence that the distribution of CFPT scores seen in the DP sample was shifted relative to that of typical controls. Some heterogeneity is likely in any neurodevelopmental population, and DP is no different. Generally, however, these findings suggest that selective STFM impairment may be relatively uncommon in this population. Instead, deficits of perceptual encoding may play a larger role in DP than currently acknowledged.