Café wall illusion

The café 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 café at the bottom of St Michael's Hill, Bristol.

This optical illusion makes the parallel straight 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 Café Wall illusion, in Perception, volume 8 (online)

External links

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