Why Optical Illusions Like These Make Your Brain Go Haywire (Wired):
“University of Bristol researchers discovered this illusion in the early 1970s while looking at the tiled wall of a café. Hence the name, Café Wall Illusion. The gray lines in between the rows of white and black squares seem to converge, but they are actually parallel. Your brain, overwhelmed by the intense and closely-spaced black-and-white contrasts, sees the gray lines as part of the tile either above or below it. The lines end up appearing higher on alternating sides, creating the trapezoidal illusion.”
More visual illusions and brain teasers: