Visual illusions -- a compendium

September 17, 2007

Academic conferences involve a lot of long speeches. To liven things up, the Vision Sciences Society always has a visual illusions night. If you can't make it to their conference, I want to direct you to an incredible Web compendium of illusions.

Many of the illusions illustrate the point that I've made before, which is that what you see is usually, but not always, a reasonably accurate depiction of reality. One such is an illustration of motion-induced blindness. As you stare at an image with both stationary and moving parts, the stationary parts seem to flicker in and out of existence.

Another is the "stepping feet" illusion, which causes you to perceive time and space out of whack. Two small rectangles move across the screen. Sometimes, they seem to be going the same speed. Other times, they seem out of step with each other. In fact, they are always parallel; the "stepping" is your mind playing tricks with you.

One of my favorites is the "Rotating Snake" illusion. The image appears to be in constant motion, but in fact it is completely stationary.

If you want to be enlightened as well as stunned and amazed, the website provides detailed explanations of each illusion, as well as references to scientific papers investigating these phenomena. The main page of the website is here. One thing it does not explain, however, is why, although vision scientists spend their lives studying the visual world, are their websites always so ugly.

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