CONTEXT-DEPENDENT INTERACTIONS AND VISUAL PROCESSING IN V1

We examined the influence of stimulus context on the response of cells in primate V1 utilising both concentric and spatially discrete stimul i. The majority of cells (63/71) showed marked patch suppression, incl uding non-oriented cells. This suppression was reduced or lost if ther e was an orientation discontinuity in the stimulus overlying the recep tive field. Cross-oriented stimuli could exert strong facilitatory eff ects so that a cell's response to an optimally oriented stimulus over its receptive field was increased by the presence of an adjacent cross -oriented stimulus. This increase appeared to involve both disinhibiti on as well as a direct facilitation. The strength of the cross-orienta tion effects was such that for some cells it seemed appropriate to def ine a cross-oriented stimulus configuration as the 'optimal' stimulus. Effects following from orientation context could be strongly influenc ed by stimulus direction. Subcortical as well as cortical interactions may contribute to these observations. It is suggested that the proper ties of the network as a whole define the responses of individual cell s and that the representation of discontinuities is an important compo nent of network function in V1.