The Neural Control of Vision
G. The Function of the On and Off Channels in Vision

This simple model in Figure 25 depicts the findings obtained with APB: The ON and OFF channels converge on many cells in the cortex but do not play an instrumental role in giving rise to the attributes of orientation, direction and spatial frequency. These attributes arise as a result of intracortical interactions aided by inhibitory circuits. Several studies had shown that administration of GABA blockers in the cortex disrupts orientation and direction selectivities.