Counter-Rotating Spirals Illusion


Look at the rotating spiral
for about 20 seconds.
Then look at something else.
screen shot Penrose Tiling


More Java applets here.

If your browser supports Java, you should see an animated image above (generated by a Java applet embedded on the page). Otherwise, you should see a static image.

Instructions for Viewing the Illusion:

The User Interface:

Start/Stop Button
The Start/Stop button starts/stops the applet's rotation thread. The button label switches from "Start" to "Stop" as appropriate.
Detach/Attach Button
The Detach Button detaches the applet from the Web page and places the applet in its own frame window. You can resize the frame window or maximize it to fill the entire screen. Once the applet has been detached, the button label changes to "Attach" and clicking the button causes the applet to re-attach to the Web page.
Speed Control
The Speed Control varies the speed of the animation in a range of 1 through 120 RPM. Click on the "+" button to increase the speed. Click on the "-" button to decrease the speed. Above a certain point, increasing the speed will have no effect due to your computer's limitations.

History of this Illusion

The illusion is an example of the "Motion Aftereffect" phenomenon. Most people have probably experienced the motion aftereffect without knowing that there is a name for it. I remember a hike my brother and I took to the bottom of the Grand Canyon after a night of too-little sleep. Every time we stopped walking, it seemed that everything I looked at was receding from me.

This effect was described in the early 19th century by R. Addams who found that he could get a strong motion aftereffect by staring at a waterfall for several seconds then shifting his gaze to something else. The illusion is sometimes called the "waterfall effect".

In 1935, the artist Marcel Duchamp produced a set of 12 rotating optical illusions called Rotoreliefs. These were meant to be observed on a phonograph turntable. Images of some of these can be viewed on the web. If you happen to have a set of "Duchamp Rotoreliefs", you are in luck because they are now very valuable (see item #63).

In the 1970's, a number of Psychologists were actively studying the phenomenon. See "The Perception of Moving Targets" by Robert Sekuler and Eugene Levinson, Scientific American, January 1977, page 60. This article gives a physiological explanation: The brain has separate motion detectors for different directions of motion. The motion detectors produce a stronger signal when there is motion and a weaker (but non-zero) signal when there is no motion. As long as all the motion-detectors are in balance with each other, you do not perceive any motion. When strongly stimulated by motion in a particular direction, the subset of motion detectors that respond to that motion become fatigued. When the stimulus is removed, the motion detectors for the opposite direction produce a stronger signal for a few seconds, until the fatigued motion detectors recover. This is thought to be the source of the motion aftereffect.

Jerry Andrus invented the multi-zone rotating spiral (with alternating expanding and contracting zones). The multiple zones produce a much stronger aftereffect than a simple spiral. Jerry is a well-known magician who has invented a number of unique illusions. He sent me several original newspaper articles describing his work including his 3-zone spiral which he calls the "Tri-Zonal Space Warper". The earliest article is in the May 12, 1978 issue of the "Willamette Valley Observer" (Eugene, Oregon, USA).

Jerry says:

"I was aware of the spiral disc that gives that after effect. My intent was to make a spiral of my own and have it so that there would be a large disc turning one direction and in the center of it you would have a small disc turning in the opposite direction. This I would accomplish with one of the discs having a tubular center that fitted over the shaft the other disc was turning on.

Starting with that in mind, at least 1977 or earlier, I rigged up a way to make the original single spiral. Since the rate of the spiral had to change as it got nearer the center. I drew the spiral with the aid of a screw cutting metal lathe. A pen on an arm was held against the face plate, and descended rapidly at first and then gradually slowed down as in got nearer the center. By turning the lathe by hand it drew a single line of the proper spiral. I then repeated this until I had the finished spiral.

I soon realized that rather than going to the trouble of having a small and a large disc I could just photographically reverse one of them and paste it on the other. This I did and ended up with three zones on the one disc.

At some stage I enlarged the disc with three zones to almost four feet and have used in talks at Harvard, UCLA, etc. Also was on That's Incredible, Omni the New Frontier program, Bill Nye the Science Guy and many more with the Tri-Zonal Space Warper and other optical illusions, and some of my magic.

Over the years I have shown the Tri-Zonal Space Warper on television in 12 different countries from Japan to South America to Europe.

In 1981 one of Senior Editors of Omni Magazine came out for a week and did a feature story on me in Omni. In the article, May, 1981, starting on page 110, you will find a copy of my Trizonal Space Warper for them to copy or cut out and put on a turntable.

My friend Professor Ray Hyman thought of that name for it.

Rudy Coby did my Tri-Zonal Space Warper on TV with my permission and you will see my name was mentioned in the credits."

Dr. Mark B. Fineman (of Southern Connecticut State University), in his book "The Inquisitive Eye" (Oxford University Press, 1981) gives two full-page spiral images meant to be observed on a phonograph turntable. One of these consists of an expanding inner spiral and a contracting outer spiral. His book has been republished in paperback by Dover (1996) as "The Nature of Visual Illusion" (very readable and a good deal at $9.95 USD -- ISBN 0-486-29105-7).

The two-part rotating spirals illusion was presented by stage magician Rudy Coby in his TV special "Rudy Coby: the Coolest Magician On Earth".

Robert Nielsen saw Rudy Coby's show and wrote a freeware DOS program, now named Hypno, which produces rotating spirals in full-screen mode. I highly recommend that you try Robert's program if you can find it. It produces a very strong motion aftereffect. In the present version of his program, the spirals are not counter-rotating (but they were in the original version). I don't know whether the counter-rotation makes any difference in the effectiveness of the illusion.

Bob Ausbourne showed me Robert Nielsen's program and suggested that I write this Java applet. Check out his SandLotScience site, an extensive collection of illusions. The background texture for this page comes from Bob's site.


Related Links:


Implementation Notes:

The applet uses double buffering.
The white spirals are drawn on a black background with 4 calls to "fillPolygon".

The image to the right of the spirals applet is a Penrose tiling generated by a DOS program that I wrote.


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