The textures in the apertures on the top and bottom are physically identical. If the left two figures in the top image are cross-fused (or right two images are divergently fused), the figure appears as 3 light grey disks visible through dark grey clouds. On the bottom, the same figure appears as 3 dark grey discs visible through light clouds. When the disparity relationships are inverted (cross fuse right two images, or divergently fuse left two images), the difference between the top and bottom figures is essentially abolished, and the figure appears as a cloudy texture visible through three holes. The first paper on these phenomena can be downloaded here, and a comprehensive theory of these and related stereo phenomena can be downloaded here.