REPRESENTATION OF MOTION BOUNDARIES IN RETINOTOPIC HUMAN VISUAL CORTICAL AREAS

Edges are important in the interpretation of the retinal image. Althou gh luminance edges have been studied extensively, much less is known a bout how or where the primate visual system detects boundaries defined by differences in surface properties such as texture, motion or binoc ular disparity. Here we use functional magnetic resonance imaging (fMR I) to localize human visual cortical activity related to the processin g of one such higher-order edge type: motion boundaries. We describe a robust fMRI signal that is selective for motion segmentation. This bo undary-specific signal is present, and retinotopically organized, with in early visual areas, beginning in the primary visual cortex (area V1 ). Surprisingly, it is largely absent from the motion-selective area M T/V5 and far extrastriate visual areas. Changes in the surface velocit y defining the motion boundaries affect the strength of the fMRI signa l. In parallel psychophysical experiments, the perceptual salience of the boundaries shows a similar dependence on surface velocity. These r esults demonstrate that information for segmenting scenes by relative motion is represented as early as V1.