Click images to enlarge.
Cafe WallThe famous Cafe Wall Illusion was discovered by Richard Gregory, on a cafe wall in Bristol, England. It develops when a staggered arrangement of light and dark bricks are separated by thin lines of 'mortar' whose brightness is intermediate between the brightness of the light and dark bricks. This creates a powerful impression of criss-crossing 'slant' in the perfectly horizontal 'mortar' lines. | 
Distorted CircleThis is a perfectly round circle, but the slanting lines appear to distort it. |
Hering's IllusionThe vertical lines are straight and parallel, but they look as if they are bowed outwards. The slanting lines simulate perspective and create a false impression of depth. Discovered by the physiologist Ewald Hering (1861). | 
Mueller-LyerProbably the most famous and most studied illusion was created by German psychiatrist Franz Müller-Lyer in 1889. Which of the two vertical line segments is longer? Although your visual system tells you that the right one is longer, a ruler would confirm that they are equal in length. |
Zollner's IllusionThe horizontal lines are parallel, but the slanting lines makes them appear to diverge. Discovered in 1860 by F. Zöllner. He described it in a letter to physicist and scholar J. C. Poggendorff, editor of Annalen der Physik und Chemie, who subsequently discovered the related Poggendorff illusion. |
 Cafe Wall Illusion Mousepad |
 Zollner Postcarts |
 Penrose/Cafe Wall Tote Bag |
