The Cafe Wall Illusion

Believe it or not, the bricks in the diagram below are arranged in exactly parallel layers. Using the controls you can adjust the alignment of the bricks and some properties of the mortar that seperates them. You should find the effect varies considerably depending on the settings... There should be an applet here! Either your browser doesn't support Java or it's disabled in your Preferences   This illusion was first described by Richard Gregory after he noticed it in the pattern of tiles on Cafe in Bristol, UK. The presence of a layer of mortar between the tiles is essential to the illusory effect. You may have noticed in the demonstration above, if the mortar thickness is set to zero then the effect disappears. Additionally the effect is strongest if the brightness of the mortar lies somewhere between that of the white and black bricks Reproduced with permission from Richard Gregory References: Gregory, R. L. & Heard, P. (1979). "Border locking and the Cafe Wall illusion" Perception 8:365-380 Gregory, R. L. & Heard, P. F. (1983). "Visual dissociations of movement, position, and stereo depth: Some phenomenal phenomena" Quarterly Journal of Experimental Psycholology 35A:217-237