It is well established that faces are processed by mechanisms that are not used with other objects. Two prominent hypotheses have been proposed to characterize how information is represented by these special mechanisms. The spacing hypothesis suggests that face-specific mechanisms primarily extract information about spacing among parts rather than information about the shape of the parts. In contrast, the holistic hypothesis suggests that faces are processed as nondecomposable wholes and, therefore, claims that both parts and spacing among them are integral aspects of face representation. Here we examined these hypotheses by testing a group of developmental prosopagnosics (DPs) who suffer from deficits in face recognition. Subjects performed a face discrimination task with faces that differed either in the spacing of the parts but not the parts (spacing task), or in the parts but not the spacing of the parts (part task). Consistent with the holistic hypothesis, DPs showed lower performance than controls on both the spacing and the part tasks, as long as salient contrast differences between the parts were minimized. Furthermore, by presenting similar spacing and part tasks with houses, we tested whether face-processing mechanisms are specific to faces, or whether they are used to process spacing information from any stimulus. DPs' normal performance on the tasks of two houses indicates that their deficit does not result from impairment in a general-purpose spacing mechanism. In summary, our data clearly support face-specific holistic hypothesis by showing that face perception mechanisms extract both part and spacing information.

Neuropsychological studies with patients suffering from prosopagnosia have provided the main evidence for the hypothesis that the recognition of faces and objects rely on distinct mechanisms. Yet doubts remain, and it has been argued that no case demonstrating an unequivocal dissociation between face and object recognition exists due in part to the lack of appropriate response time measurements (Gauthier et al., 1999). We tested seven developmental prosopagnosics to measure their accuracy and reaction times with multiple tests of face recognition and compared this with a larger battery of object recognition tests. For our systematic comparison, we used an old/new recognition memory paradigm involving memory tests for cars, tools, guns, horses, natural scenes, and houses in addition to two separate tests for faces. Developmental prosopagnosic subjects performed very poorly with the face memory tests as expected. Four of the seven prosopagnosics showed a very strong dissociation between the face and object tests. Systematic comparison of reaction time measurements for all tests indicates that the dissociations cannot be accounted for by differences in reaction times. Contrary to an account based on speed accuracy tradeoffs, prosopagnosics were systematically faster in nonface tests than in face tests. Thus, our findings demonstrate that face and nonface recognition can dissociate over a wide range of testing conditions. This is further support for the hypothesis that face and nonface recognition relies on separate mechanisms and that developmental prosopagnosia constitutes a disorder separate from developmental agnosia.