The café wall illusion is a geometrical-optical illusion in which the

parallel Parallel is a geometric term of location which may refer to: Computing * Parallel algorithm * Parallel computing * Parallel metaheuristic * Parallel (software), a UNIX utility for running programs in parallel * Parallel Sysplex, a cluster of IB ...

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 Richard Langton Gregory (24 July 1923 – 17 May 2010) was a British psychologist and Professor of Neuropsychology at the University of Bristol. Life and career Richard Gregory was born in London. He was the son of Christopher Clive Lang ...

. 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 Bristol () is a city, ceremonial county and unitary authority in England. Situated on the River Avon, it is bordered by the ceremonial counties of Gloucestershire to the north and Somerset to the south. Bristol is the most populous city in ...

. It is a variant of the shifted-chessboard illusion originated by Hugo Münsterberg. In the construction of the

optical illusion Within visual perception, an optical illusion (also called a visual illusion) is an illusion caused by the visual system and characterized by a visual perception, percept that arguably appears to differ from reality. Illusions come in a wide v ...

often each "brick" is surrounded by a layer of "mortar" intermediate between the dark and light colours of the "bricks". In the first attempt at its deconstruction, the illusion was ascribed largely to the

irradiation illusion The irradiation illusion is an illusion of visual perception in which a light area of the visual field looks larger than an otherwise identical dark area. It was named by Hermann von Helmholtz Hermann Ludwig Ferdinand von Helmholtz (31 Augu ...

(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.

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External links

An interactive web app for demonstrating the Café wall illusion
* ttps://web.archive.org/web/20190124152313/http://www.yoism.org/?q=node%2F284&plain=yes An animated proof that the horizontal lines are parallel and straightbr>The original café in Bristol on Google Maps Street View
Optical illusions {{design-stub

See also

References

External links