When you look at this pattern, ghostly black dots may appear in the intersections. They always show up wherever you are not looking, appearing and disappearing as you scan the figure. If you let your eyes rest on one dot you can make the nearest black dots fade. But as soon as you move your eyes again they reappear. As our light receptors cope with this high contrast image they are constantly switching between an excited and rested state. While the excited receptors work well, the resting receptors continue to send weak, conflicting signals to the brain. To make a black dot disappear, simply look at it.