Face Specific vs. Expertise Hypotheses: Insights into the Underlying Mechanisms of Face Processing in Prosopagnosia

A prominent debate in visual perception centers on the nature of mechanisms underlying face processing. One side of this debate argues that faces are processed by specialised mechanisms that are not involved in any form of object processing. By contrast, the other side argues that faces are processed by generic mechanisms common to all objects for which we are experts. To distinguish between these two hypotheses, I investigated whether participants with impaired face processing (developmental prosopagnosia) can acquire expertise with novel objects called greebles. To do so, I recruited 10 developmental prosopagnosics and 10 neurotypical control participants. All participants completed a standard training program for developing expertise with greebles, as well as two similar training programs with upright faces and inverted faces. Prosopagnosics were able to acquire expertise with greebles to the same extent as controls but were impaired when learning upright faces. These results demonstrate that deficits for face processing in individuals with prosopagnosia are dissociated from their ability to gain expertise with objects. Overall, the results support the hypothesis that face processing relies on specialised mechanisms, rather than generic expertise mechanisms. Despite their deficits, though, prosopagnosics still showed some evidence of learning with upright faces and showed better learning with upright faces than inverted faces. These findings suggest that prosopagnosics have face-specific mechanisms that are somewhat functional, and that training could be a useful rehabilitation tool in developmental prosopagnosia. Finally, I found substantial heterogeneity among the patterns of performance of the prosopagnosics, suggesting that further investigations into the subtypes of prosopagnosia are warranted