Effects of structural similarity on neural substrates for object recognition.

Human occipitotemporal cortex (OTC) is critically involved in object recognition, but the functional organization of this brain region is controversial. In the present study, functional magnetic resonance imaging (fMRI) signal changes were recorded in humans during an animal-matching task that parametrically varied degree of structural (i.e., shape) similarity among the items. fMRI signal in the mid- to anterior-fusiform gyrus increased as animals overlapped more in terms of structure and as reaction time increased. In contrast, relatively more posterior aspects of the fusiform gyrus and inferior occipital cortex showed greater fMRI signal when the animals overlapped less in terms of structure. A similar organization emerged when three-dimensional geometric shapes were matched, indicating that OTC is differentially tuned to varying degrees of overlap in object structure, regardless of taxonomic category. We discuss how the present findings fit in with current functional neuroanatomical approaches to object recognition.