The visual system consists of structures including the eye, optic nerve, and visual cortex. The activity of this system begins with the visual representation of the stimuli in the external world. The pupil regulates the amount of light according to its brightness (by contracting and dilating). You can think of your eye as a camera. Light enters the eye through its pupil, focuses on the cornea and lenses, and then reaches the rods and cones, the receptor cells on the retina (Figure 4.3). The role of receptor cells is to convert the light energy into neural messages. The cones are plentiful in the fovea, but they become less and less prevalent as one moves away from the fovea to the retina’s periphery. The opposite is true for rods. The rods aren’t located in the fovea and the density increases toward the periphery.