Café wall illusion
The café wall illusion is a geometrical-optical illusion in which the parallel straight dividing lines between staggered rows with alternating dark and light "bricks" appear to be sloped, not parallel as they really are.
It was first described under the name Kindergarten illusion in 1898, and re-discovered in 1973 by Richard Gregory. According to Gregory, this effect was observed by a member of his laboratory, Steve Simpson, in the tiles of the wall of a café at the bottom of St Michael's Hill, Bristol. It is a variant of the shifted-chessboard illusion originated by Hugo Münsterberg.
In the first attempt at its deconstruction, the illusion was ascribed largely to the irradiation illusion (apparent greater size of a white area than of a black one), and the image disappears when black and white are replaced by different colours of the same brightness. But a component of the illusion remains even when all optical and retinal components are factored out. Contrast polarities seem to be the determining factor in the tilt's direction.
- Pierce, A. H. (1898). "The illusions of the kindergarten patterns" (PDF). Psychological Review. 5 (3): 233–53. doi:10.1037/h0070595.
- Gregory, R. L.; Heard, P. (1979). "Border locking and the Café Wall illusion" (PDF). Perception. 8 (4): 365–80. doi:10.1068/p080365. PMID 503767.
- Münsterberg, H. (1897). "Die verschobene Schachbrettfigur". Zeitschrift für Psychologie. 15: 184–88.
- Morgan, M. J.; Moulden, B. (1986). "The Münsterberg figure and twisted cords". Vision Research. 26 (11): 1793–1800. doi:10.1016/0042-6989(86)90130-6.
- Pierce, A. H. (1901). Studies in Auditory and Visual Space Perception. London: Longmans Green.
- Westheimer, G. (2007). "Irradiation, border location and the shifted-chessboard pattern". Perception. 36 (4): 483–94. doi:10.1068/p5646.
- Kitaoka, A; Pinna, B.; Brelstaff, G. (2004). "Contrast polarities determine the direction of Cafe Wall tilts" (PDF). Perception. 33 (1): 11–20. doi:10.1068/p3346. PMID 15035325.
- An interactive web app for demonstrating the Café wall illusion
- An interactive version of the Café wall illusion that allows for adjusting the offset and turning the black boxes into white boxes
- An animated proof that the horizontal lines are parallel and straight
- The original café in Bristol on Google Maps Street View