1ST-ORDER ANALYSIS OF OPTICAL-FLOW IN MONKEY BRAIN

Optical flow is a rich source of information about the three-dimension al motion and structure of the visual environment. Little is known of how the brain derives this information. One possibility is that it ana lyzes first-order elementary components of optical flow, such as expan sion, rotation, and shear. Using a combination of physiological record ings and modeling techniques, we investigated the contribution of the middle superior temporal area (MST), a third-order cortical area in th e dorsal visual pathway that receives inputs from the medial temporal area (MT). The results show (i) that MST cells, but not MT cells, are selective for elementary flow components (EFCs) alone or their combina tion with translation, (ii) that MST cells selective for an EFC do not extract this component from a more complex motion pattern, and (iii) that position invariance as observed in MST is compatible with an inpu t arrangement from MT cells matching the selectivity of MST neurons.