Cortical cells ; Bar and edge detectors, or spatial frequency filters

Until the pioneering work of HUBEL and WIESEL (1, 2, 3), visual scientists could do little more than guess about the functions of cells in visual cortex and the manner in which complex patterns were analyzed. Their initial reports, however, established that cells in Area 17 of cat (and also monkey) were quite unresponsive to full-field illumination, requiring more specific patterns to elicit a response. Their receptive field (RF) maps of simple cells showed an elongated excitatory center and inhibitory flanks, or vice versa; or two adjacent excitatory and inhibitory areas. Initially HUBEL and WIESEL (2) reported that there was summation within the excitatory and inhibitory regions and an antagonism between them. As we shall see, such summation, if true, would have implications not at all foreseen at the time, and would lead one, in fact, to a quite different model of what such cells do from the one which they actually proposed.