Jason W. Brown
The traditional neurological approach to visual perception assumes that an object is the result of a chain of events object is the result of a chain leading over stations in a sensory pathway. This pathway leads from retina to the lateral geniculate bodies of thalamus which relay the signal to visual (striate) cortex. Cells in the visual cortex respond to various features in the cortex respond to various features in the stimulus array, features which are subsequently combined to a pattern perception over the circumstriate zone. From this region connections exist to convey the information to other neocortical sites for "higher" or more complex processing. For example, there are pathways to the inferotemporal region which are thought to relate percepts to meanings, or provide a constant update of the visual environment to an experiential and/or spatial map of the world.
This general model of visual perception has dominated neuropsychological thinking for a good many years, and, in fact, has served as a basis for theorizing about almost all neuropsychological functions. The centerpiece of the model is the prominence given to the geniculo-cortical pathway, and the assumption that the cortical retinal map, that this pathway elaborates, is the starting point in the brain's construction of an object. The difficulties with this account have only recently become apparent in light of anatomical and experimental studies. For one thing, we now know that the connectivity of the visual system is extremely complex with many projections not accounted for by the geniculo-cortical model; for example, extra-striate geniculo-cortical projections, extra-geniculate thalamic projections to nonstriate cortex, as well as various efferent subcortical fibers descending from visual cortex (Vastola, 1968). There are also wholly intrinsic systems which seem to have a visual function. Studies of posterior____________________