Created by Mary Coffelt and her colleagues at the Barrow Neurological Institute, this version of Akiyoshi Kitaoka's "Bulge" illusion uses strategically placed white and purple M&Ms to warp your perception of a checkerboard built from legos of the same color. (Hit the jump to see a video of the Bulge illusion in action.)
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Okay, I see the illusion, I see what patterns one must add to create the illusion, but I don't get the reason behind the illusion. Why does our brain process flat, simmetric checkboard patern with diagonal lines of dots as a spherical bulge?