I would have mentioned this earlier, but the excellent Illusion Sciences blog went over its Google Pages hosting quota, so I couldn't snag myself a copy of the SWF file to host on my own site.
Now the blog's back, so here it is:
Brilliant, huh?
More info at Illusion Sciences.
UPDATE: Here's a nifty HTML5 version of the same illusion, as per caerphoto's comment below.
18 December 2008 at 12:56 pm
Optical Illuuuuuusion!
Brilliant.
18 December 2008 at 2:42 pm
It should be noted that (while cool) something on that site (http://www.illusionsciences.com/) ate my Opera browser twice.
Opera users (yes, all 6 of us) should probably just open it in Firefox (which didn't die).
18 December 2008 at 2:49 pm
On the topic of Illusions, my favourite genre is Anamorphosis. My favourite examples are the works of artist Felice Varini:
http://www.varini.org/02indc/indgen.html
The site is in french, but don't let that put you off - you may need to click on the "hors point de vue" link if you want to see the work from another point of view.
18 December 2008 at 3:20 pm
Weeeeeeeeeeird.
18 December 2008 at 5:39 pm
I can't believe someone gets to make this stuff professionally. Best Job Evar!
18 December 2008 at 7:18 pm
@ j:
Worked perfectly well in my Opera browser. Perhaps your Flash needs updating.
18 December 2008 at 8:32 pm
Gaah, my brain is broken!
19 December 2008 at 1:34 am
In addition to what the description says, I seem to see both rotating clockwise at what appears to be a much higher framerate if I look at them on the edge of my field of vision. (they look a bit jerky if I stare at either dot).
19 December 2008 at 5:55 am
No matter which I look at, I see both rings spinning counter-clockwise. 90% of these illusions don't do what they're "supposed" to do for me.
19 December 2008 at 5:56 am
Hmm, I just switched to Internet Explorer and the flash had a green background....and the illusion worked.
21 December 2008 at 5:15 pm
That .swf file is death. It causes Maxthon to chew up 50% of available core and become slower than anything. I blocked it, because otherwise I couldn't look at the blog without disabling flash. Something is wrong with it.
22 December 2008 at 9:45 am
@Bedlam:
I suspect it has more to do with my crummy work PC than Opera, but it should be noted that FF handled the page okay.
I think the lesson we can take away from this is that Flash (and Shockwave) needs to die a horrible, horrible death. As soon as possible.
22 December 2008 at 1:02 pm
Yes, the current version of Flash on Windows - and I presume also Mac OS, because Flash for Mac OS always sucks worse than Flash for the PC - will peg one processor core when that Flash animation is running. This is a fairly common symptom, for what it's worth.
If you've got more than one processor core, though, you probably won't even notice, if at least you've got a desktop PC. (A laptop may suddenly start making more fan noise than usual.)
26 December 2008 at 11:30 pm
Hmmm... Each pentagon of circular windows rotates counterclockwise, but I'm having real trouble making out for sure whether the black and white bars that you see through them are stationary or rotating clockwise. In any event, I'm pretty sure the described illusion wouldn't work without those black and white bars, i.e., if the circular windows just showed you another color or a polka-dot pattern or something.
6 October 2012 at 3:48 am
Apologies for commenting on such an old post but I only recently discovered it.
Anyway, because Flash is terrible I made my own version of this illusion using CSS and some images. It's bigger, it ought to run a bit smoother, and as a bonus it even works on smartphones. Also it has a checkbox to show what's going on with the various spinning bits.
9 October 2012 at 10:48 am
Anyway, because Flash is NOT terrible I made my own version of this illusion using Flash. It's bigger, it runs a lot smoother, and as a bonus it even works at full speed on my 3 year old HTC Desire.
Made this thing in 30min and cut the CPU occupancy by 10 or 20. The original was clearly not done by someone who had efficiency in mind. But yeah if a Professor of Psychology uses Flash to demonstrate an illusion, it's clearly the technology's fault that the result it not optimized.