Fading Dot shows the effect of fatigue on the visual system. A screen contains a green background with a fuzzy-edged red spot in the middle. If a person stares intently at the red spot, it seems to fade away. For many people, the dot fades completely away; for others, a vague yellow smudge replaces it; and for others, the background fades as well. The visual receptors in the eye need a changing stimulus to avoid shutting down. That stimulus is usually provided by sharp borders being moved by the jittering motion of the eyeball. Because this dot doesn’t have sharp borders, the eye has nothing on which to focus, and the image fades.