Cells on the dark edge of the bar of light are not stimulated, but are inhibited by their neighbors in the light. They respond with a strong inhibition on up the neural chain. It is in this manner that eyes tend to emphasize edges and find large areas without changing light density very boring indeed. Visual processing takes place in the mammalian retina and brain Fig 11-32. The retina has two types of receptor cells.
Rods are sensitive to weak light and bleached out by strong light.
They are only black-white, and are not found in the fovea . Cones are packed in the fovea and less dense in the peripheral areas. They are sensitive to stronger light and also contain one of three pigments that allow them to interpret color. They are thought to be responsible for lateral inhibition. Receptor cells and horizontal cells feed onto bipolar cells which lead up to the inside of the retina and contact amacrine cells which also lie horizontally, but at this higher level and ganglion cells which are the output cells and whose axons form the optic nerve.