Distortion Illusions

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Cafe Wall

The 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 Circle

This is a perfectly round circle, but the slanting lines appear to distort it.

Hering's Illusion

The 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-Lyer

Probably the most famous and most studied illusion was created by German psychiatrist Franz M�ller-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 Illusion

The horizontal lines are parallel, but the slanting lines makes them appear to diverge. Discovered in 1860 by F. Z�llner. 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.