Receptive Field Organization in Areas 17, 18 and 19 of the Cat

Abstract

As pointed out in Chapter 2, each visual neuron, and thus also each visual cortical neuron has a receptive field i.e. a small retinal region, or its counterpart from the visual field, from which it can be influenced. Receptive field organization refers to the layout of the different parts (or subregions) within the receptive field (RF). When tested with different visual stimuli, cortical cells display a wide variety of response patterns. Exactly as zoologists and botanists exploring new continents a few centuries ago, neurophysiologists studying new cortical areas need a taxonomy to describe this variety. This allows them to compare the results of different experiments during each of which they can only observe a limited number of cortical cells. It also makes possible exchanges of information between experimenters. In principle, each functional property of cortical cells, as orientation selectivity, binocularity, direction selectivity, velocity sensitivity etc. can be used to derive a taxonomy. And indeed many of the results which will be presented in the subsequent chapters are just examples of such taxonomies. However, in as much as these different properties are independent, one would need a large set of such taxonomies and thus of experimental tests, in order to categorize the cells. Therefore, one has to look for a more fundamental taxonomy which in a way could contain or imply all the others. The properties of a cortical cell result from the inputs to the cell (i.e. different afferents converging onto the cell) and the intrinsic (i.e. membrane) properties of the cell. One of the important contributions of Hubel and Wiesel (1959, 1962, 1965) to cortical physiology has been to use the receptive field organization,which to a certain extent reflects the input pattern, to derive a taxonomy for the visual cortical cells.