Edit the Illusion
About the Spine Drift Illusion
This is Kitaoka's "Spine Drift" illusion. In the image you can see an array of spines with the a gap around a square in the middle. If the middle square appears to float or move, you are seeing the illusion! It is strongly affected by eye movements, thus perceived differently by different people. To enhance the affect, try shaking either the screen or your head.
If the center and outer spines are parallel or at 180 degrees, then there is no illusion. If the inner spines are at 90 degrees either way, then the illusion occurs. You can see this by rotating the inner square.
Information from Michael’s Visual Phenomena & Optical Illusions.