Prosopagnosia as a deficit in encoding curved surface

RP is a case of "developmental" prosopagnosia who, according to brain-imagi ng segmentation data, shows a reduction in volume of a limited set of struc tures of the right hemisphere. RP is as accurate as control subjects in tas ks requiring the perception of nonface objects (e.g., matching subordinate labels to exemplars, naming two-tone images), with the exception of one per ceptual task: The matching of different perspectives of amoebae-like stimul i (i.e.. volumes made of a single smooth surface). In terms of speed ("effi ciency") of responses, RP's performance falls clearly outside the not nial limits also in other tasks that include "natural" but nonface stimuli (i.e. , animals, artifacts). Specifically, RP is slow in perceptual judgements ma de at very low (subordinate) levels of semantic categorization and for obje cts and artifacts whose geometry present much curved features and surface i nformation. We conclude from these analyses that prosopagnosia can be the r esult of a deficit in the representation of basic geometric volumes made of curved surface. In turn, this points to the importance (necessity) for the normal visual system of such curved and volumetric information in the iden tification of human faces.