What is meant by impaired configural processing in acquired prosopagnosia?

Apperceptive prosopagnosia is supposedly characterised by impaired configural processing, which could refer to either perception of spatial structure or holistic mechanisms. Ten prosopagnosic patients were tested with (i) dot patterns, to determine if manipulations of complexity, size, orientation, or the regularity of global structure generated effects consistent with the holistic hypothesis; and (ii) hierarchical letters, to probe for a global 'whole-object' processing deficit. With dot patterns (experiment 1) patients were impaired even for simple two-dot stimuli, but did better with more complex patterns, when size or orientation varied, or with a regular global structure. In experiment 2, they demonstrated normal latency effects of global-level processing. Apperceptive prosopagnosia, including that from lesions encompassing the right fusiform gyrus, is thus associated with a 'configural deficit' that impairs perception of spatial structure, not just for faces but also for non-facial patterns. While it cannot be concluded that holistic processing is entirely normal in these subjects, their performance shows significant modulation by whole-object structure, indicating that some whole-object processing is occurring in these patients.