An fMRI study of the selective activation of human extrastriate form vision areas by radial and concentric gratings

The ventral form vision pathway of the primate brain comprises a sequence o f areas that include V1, V2, V4 and the inferior temporal cortex (IT) [1]. Although contour extraction in the VI area and responses to complex images, such as faces, in the IT have been studied extensively, much less is known about shape extraction at intermediate cortical levels such as V4. Here, w e used functional magnetic resonance imaging (fMRI) to demonstrate that the human V4 is more strongly activated by concentric and radial patterns than by conventional sinusoidal gratings. This is consistent with global poolin g of local Vl orientations to extract concentric and radial shape informati on in V4. Furthermore, concentric patterns were found to be effective in ac tivating the fusiform face area. These findings support recent psychophysic al [2,3] and physiological [4,5] data indicating that analysis of concentri c and radial structure represents an important aspect of processing at inte rmediate levels of form vision.