Shape configuration and category-specificity.

We examined the neural correlates of visual shape configuration, the binding of local shape characteristics into wholistic object descriptions, by comparing the regional cerebral blood flow associated with recognition of outline drawings and fragmented drawings. We found no areas that responded more to fragmented drawings than to outline drawings even though fragmentation had a clear impact on recognition performance. Instead, a region extending from the inferior occipital gyri to the middle parts of the fusiform gyri was activated during shape configuration of both outline drawings and fragmented drawings. We also examined whether fragmentation had different impact on the recognition of natural objects and artefacts and found that recognition of artefacts was more affected by fragmentation than recognition of natural objects. Thus, the usual finding of an advantage for artefacts in difficult object decision tasks, which is also found in the present experiments with outlines, is reversed when the stimuli are fragmented. This interaction between category (natural versus artefacts) and stimulus type (outlines versus fragmented forms) is in accordance with predictions derived from a recent account of category-specificity and lends support to the notion that category-specific impairments can occur for both natural objects and artefacts following damage to pre-semantic stages in visual object recognition. The implications of the present findings are discussed in relation to theories of perceptual organization, visual object recognition and category-specificity.