The Human Visual System is described from photon absorption in the photoreceptors, to signal processing in the retina, to the act of “seeing.” The principal vision processing units are the bipolar and the horizontal cells, located in the outer plexiform layer, with their center-surround receptive fields The retinal ganglion cells also possess center-surround receptive fields. The human visual system is very effective in locating borders of objects, or regions in an image where the contrast is rapidly changing. Lateral inhibition is a general mechanism in all sensory systems, including the visual system, to enhance contrast. Further processing of the signals from the retina occurs in the primary visual cortex of the brain.