Spinning Illusion
Last updated: Wednesday, October 31, 2001.

An optical illusion arrived in my mailbox today (June 25, 2001):

To try to figure out how it works, I wrote a little Java applet.

The illusion seems to be caused by the image getting bigger and smaller (this can be seen by the fact that animating the size has the same effect as moving your head). There are two effects causing the illusion: shape and shading; if you have no skew, but you do have shading you get the effect, and if you have skew but no shading you get the effect. These two things seem to cancel each other out if you leave shading on and make the skew negative. My guess is that the illusion is the result of the shape or shading somehow making your brain think that when the shapes move radially out from the center, they also move in the direction of the shape or shading. If you have a better idea, or a clearer explanation, please email me. :-)

Here are some more web pages with optical illusions on them:

See also:
Brett Allen (brett@snazzorama.com)
This page is Copyright 1994-2006, Brett Allen.