< previous | next >              Close window Eggs and cavities: In this graphic, the shaded disks are all identical except that half of them are light on top and the rest are dark on top. The ones that are light on top are seen as eggs bulging out from the screen, whereas the ones that are dark on top are seen as cavities. This is because the visual areas in your brain have a built-in sense that the sun is shining from above, which makes bulges (eggs) light on top and concavities light below. © | Updated October 2001