How brain fills gaps

A vase from China's Song dynasty demonstrates the use of very faint contrast borders to create the illusion of shading on a one-color background. The phenomenon is known as edge induction. The image of the vase is overlaid over the Cornsweet illusion, in which the left half of a rectangle divided in two looks lighter and the right area darker. Holding one's hand over the center of the image reveals that the left and the right are in fact the same color. The brain "fills in" the color on the left and the right in response to information from the middle border. Courtesy of Anna Roe