Both stimuli on top look like cubes and both stimuli on bottom look like hexagons with dots inside. Try to free-fuse these stereograms. If binocular disparity was critical, disparity's effect will be perceived with both stereo-pairs shown in this demo. If you fuse this display, you will discover that varying binocular disparity only affects the stereo-pair on bottom.  On top, you will see a rigid cube oscillating to the right and left. See the text for an explanation of this difference.