Theory of non-classical receptive field phenomena in the visual cortex

In many experiments it has been found that stimuli outside the classical receptive-field of orientation-selective cells in the visual cortex can strongly modulate the response properties of these cells. Typically, stimuli with orientation contrasts lead to enhancement, whereas iso-orientation stimuli lead to suppression of the neuronal activity, but these phenomena in general depend in a complicate manner on various parameters like stimulus configuration, contrast, and geometry. In this contribution, we develop a simple theory for such non-classical receptive-field phenomena. We explain the basic mechanisms by a fixed-point analysis. Within this analysis, center-surround experiments can be described by trajectories in parameter space. This allows for a systematic variation of the coupling and stimulation constants. We show that the strength or sign of the enhancement or suppression should not only vary with the experimental paradigm but also with the position of the cell within the cortex. Our results suggest that non-classical receptive-field phenomena are mediated through orientation-specific lateral excitatory interactions.