Move the bricks back and forth and notice the strange distortions
in the rectangular brick pattern. If the bricks are aligned
as they are in the beginning or if they are organized in a checkerboard
pattern, the effect disappears.
Change the brightness of the mortar by clicking on the top or
bottom of the brightness arrow (you can click and hold to change
continuously). Notice when the effect goes away.
The Cafe Wall Illusion was first described by Dr. Richard Gregory.
Dr. Gregory is a good friend of the Exploratorium and director
of
The
Exploratory Hands On Science Museum
in Bristol, England.
Dr. Gregory observed this curious effect in a pattern of tiles
on a cafe wall in Bristol and has kindly granted us permission
to display his picture of this cafe below. Note that the effect
is not visible in the picture due to the small scale of the
tiles.
