Benham’s Disk is a 22-inch diameter black and white disk mounted on a wall. Half of the disk is black, and the other half is a broken series of black lines on a white background. When the visitor pushes a button, the disk begins spinning, and the visitor sees colored lines. The colors that appear depend on individual perception, as well as on how fast and in which direction the disk is spinning. While nobody knows for certain why the colors appear, it is thought that lateral inhibition and the different rates of stimulation for the color-sensitive cells in the retina are involved.