Found this today: Here is a very cool picture of directionally selective retinal ganglion cells (go from the retina in the eye to the lateral geniculate (or optic tectum) in the brain). These cells are asymmetrical and only detect movement going up in the visual field. I think the different colors in this digital confocal microscope picture are based on the vertical position in the flatten out retina, which was removed from the eye for imaging. Remember, not all visual processing goes on in the brain. On the other hand, the retinal is considered part of the CNS (based on embryology, it is derived from the neural plate), not the peripheral nervous system. The long lines are their axons going to the optic nerve, the blobs are the cell bodies, the branchy parts are their dendrites, where they receive inputs for cells more directly linked to the photoreceptors. I got the image from here and a related article by those who made it is here.