This is just too weird. As you look at this image (attempts to shrink the image to fit this page broke the very powerful affect; go ahead, it’s worth the click!), the circles in your peripheral vision seem to move. You quickly glance right or left and fix your gaze on one of the colorful spirals. Nope, not moving … but wait, now that one in the middle seemed to move.
The first time I saw this it was late at night and I sort of thought it worked because I was tired. After viewing the page numerous other times, it seems that no, the perceptual trick works every time the image is viewed.
And, if you liked that one, here’s a whole page of goodies! Some of these did seem to work better when tired. A number of them only work when one bobs one’s head back and forth to induce the effect. Imagine hordes of bored office workers viewing the page and bobbing their heads like so many chickens! 🙂