caf wall illusion

The caf wall illusion is an optical illusion, first described by Doctor Richard Gregory. He observed this curious effect in the tiles of the wall of a caf at the bottom of St Michael's Hill, Bristol. This optical illusion makes the parallel straight horizontal lines appear to be bent. It is essential for the illusion that each "brick" is surrounded by a layer of "mortar" (the gray in the image). This should ideally be of a colour in between the black and white of the bricks.

References

Richard Gregory and Priscilla Heard: Border locking and the Caf Wall illusion, in Perception, volume 8 (online)

External links

Interactive version of the Caf wall illusion (Requires Shockwave browser plugin)
Another interactive version (Requires Java-capable browser)

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