The Neural Control of Vision
C. The Retina

Figure 6 shows schematically the layout of the receptive fields of the midget and parasol cells of primates that have red, green and blue cones. In central retina the receptive field center of midget cells is comprised of just a single cone which automatically renders them color selective. By contrast, parasol cells get a mixed cone input both in the center and the surround of their receptive fields. As shown on the bottom, the midget cells respond to light falling into the receptive field center in a relatively sustained fashion whereas parasol cells respond transiently.