The Neural Control of Vision
H. The Function of the Midget and Parasol Channels in Vision

Figure 27 provides a schematic of the wiring of the midget system in the retina. The receptive field center of midget retinal ganglion cells is comprised of just a single cone. This makes them automatically color selective. There are several classes of midge cells each of which receives input for their receptive field center from a different cone type. Red and green-selective cones connect both with ON and OFF bipolars hence giving rise to red ON and OFF and green ON and OFF ganglion cells. There is still a debate as to whether the blue cones also do this. It has been shown that only one out of 8 cones is blue and that most blue selective ganglion cells give ON responses. The surround mechanism of retinal ganglion cells is brought about by the horizontal systems in the retina, produced by the horizontal and amacrine cells.