Lateral inhibition increases the contrast and sharpness in visual response. This phenomenon already occurs in the mammalian retina. In the dark, a small light stimulus will enhance the different photoreceptors (rod cells). The rods in the center of the stimulus will transduce the "light" signal to the brain, whereas different rods on the outside of the stimulus will send a "dark" signal to the brain due to lateral inhibition from horizontal cells. This contrast between the light and dark creates a sharper image. (Compare unsharp masking in digital processing). This mechanism also creates the Mach band visual effect.