Physics:Café wall illusion

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Short description: Optical illusion
The café wall illusion. The horizontal lines are parallel, despite appearing to be at different angles to each other.
The same image, with colors (ff0000 and ffcccc) of lower contrast, no longer displaying the 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,[1] and re-discovered in 1973 by Richard Gregory.[2] 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.[3]

In the construction of the optical illusion often each "brick" is surrounded by a layer of "mortar" intermediate between the dark and light colours of the "bricks".[4]

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),[5] and the image disappears when black and white are replaced by different colours of the same brightness.[6] 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.[7]

Richard Gregory visits the original café wall on St Michael's Hill, Bristol, in February 2010
Architecture inspired by the café wall illusion, at Melbourne Docklands

See also


  1. Pierce, A. H. (1898). "The illusions of the kindergarten patterns". Psychological Review 5 (3): 233–53. doi:10.1037/h0070595. 
  2. Gregory, R. L.; Heard, P. (1979). "Border locking and the Café Wall illusion". Perception 8 (4): 365–80. doi:10.1068/p080365. PMID 503767. 
  3. Münsterberg, H. (1897). "Die verschobene Schachbrettfigur". Zeitschrift für Psychologie 15: 184–88. 
  4. 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. 
  5. Pierce, A. H. (1901). Studies in Auditory and Visual Space Perception. London: Longmans Green. 
  6. Westheimer, G. (2007). "Irradiation, border location and the shifted-chessboard pattern". Perception 36 (4): 483–94. doi:10.1068/p5646. 
  7. Kitaoka, A; Pinna, B.; Brelstaff, G. (2004). "Contrast polarities determine the direction of Cafe Wall tilts". Perception 33 (1): 11–20. doi:10.1068/p3346. PMID 15035325. 

External links