Figure 8.27: A depth illusion created by binocular disparity The two patterns are constructed to appear as they would to the left and right eye, respectively, if the dark square were actually a certain distance in front of the white square (like that shown in Figure 8.26). In order to experience the three-dimensional effect, hold the book about a foot in front of your eyes and let your eyes drift in an unfocused way until you see double images of everything. You will see four renditions of the white frame with a darker square center—two renditions of (a) and two of (b). When all four of these images are clear, converge or diverge your eyes a little in order to get the right-hand image of (a) to sit right atop the left-hand image of (b). You have fused your left-eye view of (a) and your right-eye view of (b) into a single image, which now appears to be three-dimensional: The dark square seems to float in space in front of the white square.