The original version of this illusion involved a piece of paper with this strange spiral on it, and you needed a method of getting the spiral to spin in order to create the illusion.
Now, thanks to the power of the computer, all the hard work has been done for you, and you can run the illusion right here on your screen.
Click here to download a small application file (Optical.exe 22KB). When you have downloaded the file, just double click to run the pinwheel on your computer screen. You need to stare at the centre of the pinwheel for 30 seconds, and then look away from the screen. Wow!
Thanks to Jerry Andrus who invented this illusion, which he calls the Tri-zonal Space Warp! And thanks to Jodi who drew this example of the illusion to our attention.