COMPUTATIONAL MODELS OF CORTICAL VISUAL PROCESSING

The visual responses of neurons in the cerebral cortex were first adeq uately characterized in the 1960s by D. H. Hubel and T. N. Wiesel [(19 62) J. Physiol. (London) 160, 106-154; (1968) J. Physiol. (London) 195 , 215-243] using qualitative analyses based on simple geometric visual targets, Over the past 30 years, it has become common to consider the properties of these neurons by attempting to make formal descriptions of the transformations they execute on the visual image, Most such mo dels have their roots in linear-systems approaches pioneered in the re tina by C. Enroth-Cugell and J. R. Robson [(1966) J. Physiol, (London) 187, 517-552], but it is clear that purely linear models of cortical neurons are inadequate. We present two related models: one designed to account for the responses of simple cells in primary visual cortex (V 1) and one designed to account for the responses of pattern direction selective cells in MT (or V5), an extrastriate visual area thought to be involved in the analysis of visual motion. These models share a com mon structure that operates in the same way on different kinds of inpu t, and instantiate the widely held view that computational strategies are similar throughout the cerebral cortex, Implementations of these m odels for Macintosh microcomputers are available and can be used to ex plore the models' properties.