Here’s a neat optical illusion, go to this website and stare at the dancer. Is she rotating clockwise or counter-clockwise? And can you change it at will?
She appears to rotate clockwise to me, but if I focus elsewhere, and let only my peripheral vision see the rotating dancer, she appears to rotate counter-clockwise!
Link – Thanks No Name!
biltmore
She’s rotating clockwise for me as well. Guess I’m a “right brainer” … whatever the hell that means. Haha.
Ali S.
If you look carefully you’ll see the image just jump for a second and then it’ll spin the other way. 
Michael
Count beats of the rotating feet as “right/left” for a moment, then purposefully reverse the pattern to what you know is wrong; any change in strong internal beat associated with the pattern will change the direction.
Neat find.
Xayzer
Ali S. is right. It’s a trick. Every couple of seconds (or about a minute) the dancer changes direction from clockwise to anti-clockwise and vice-versa. You can barely see this occurrence, but if you look closely and don’t blink at the exact moment, you’ll notice.
Nonimus
This is brilliant. Perception is reality. I love how people “know” what’s going on. Truly, we see the world not as it is, but as we are.
After staring/playing with this for a while, I can now consciously switch my perception of the dancer’s rotation. Quite an interesting optical illusion.
When she is spinning left, it appears that her left arm and leg are raised. And when she is spinning right, it appears that her right arm and leg are raised.
Have several of your mates look at this together, and you may find they are perceiving the same moment differently.
saehn
The easiest way I found to get her to “flip” was to focus on a point about six inches below the monitor, with her still in my peripheral vision. That gives you just enough visual cues to communicate “spin” but not enough to lock in a direction.
The thing is, the animation for this figure’s spin is exactly the same one “direction” or the other. Your mind just picks a direction. Look at the image linked below. If you think about it, either:
* her back is to us, her right leg & arm are raised, and she’s spinning clockwise, or
* her chest is to us, her left leg & arm are raised, and she’s spinning counter-clockwise
http://i37.photobucket.com/albums/e83/saehn/spinning-girl.jpg
It works because she’s just a silhouette. If it were filled in with more visual data, there’d be no ambiguity as to the spin direction. Pretty nifty! 
Monster
Nonimus is right. I don’t remember if this was posted here before or elsewhere, but the animation is just a loop, no tricks involved. If you and someone else watch it at the same time, it will switch directions for both people at different times.
jwh2103
Ali S. and Xayzer, you are both WRONG! I loaded the GIF up in a frame-by-frame animation editor, and it’s only 34 frames long. So there can’t be a sneaky change after a while.
Alex
No, it can’t be a flip encoded in the animation itself because you can rotate her in your mind at will.
FetishForPerception
Took me a while to be able to control which direction she spins in! Spun me out completely! :S
Toast
Take a look at her with some panties drawn on. The same frame can be interpreted to be her genitals or her buttocks. http://bay01.imagebay.com/full_view.php?view=21804_spin.jpg
Hallie
You guys need to watch it harder. See which leg she is standing on while she is spinning. After she has switched directions, see that she’s standing on a different leg. It’s not an optical illusion. We perceive the direction she is spinning because of which breast appears first and such-like. There’s no two ways about which way she spins. It’s not an optical illusion, it’s a trick, and I’m trying to find out where it came from.
marc
It’s an illusion, you can control which way she spins. Turn your head to the right and cover your right eye, then to the left and cover your left eye. If you time it right you can make her move her leg from side to side without going all the way round! You’ll looks stupid though, so don’t do it at work.
Brian
I got her to rock back in forth for a while so that I never saw her “back”. I thought it was a trick too, but I got to a point where I could control her by watching her shadow (and unless there are bursts of her rocking instead of spinning every 30 seconds or so, its not a trick). I was counter clockwise by the way, which is wierd because I always test the other way.
joeb
Those of you who think it’s a trick make me laugh. Just watch the illusion with a group of people at the same time! Guarantee that some people will see it going different ways. It’s a silhouette, and so has missing information. Take a look at your own shadow on the wall, and try to figure out whether you are looking at a mirror reflection of yourself, or at your own back. There is no difference.
Cathy D.
I’m sorry, I must be seeing something different than everyone else is… she ALWAYS rotates CCW to me, and I absolutely do not see how she can be supposedly changing direction. Weird.
Ryan
This is stupid. This is an animation and if you watch it it starts to spin the other way. I am sick of these stupid tricks!!!!
Jess
As someone who has studied cognition and perception, I can safely say that this is most certainly an optical illusion.
This illusion is an example of what is called the ambiguous motion effect, which is caused by (as a couple of people have already mentioned) an absence of depth cues. Your brain will attempt to make sense of this image by selecting a random direction that you will percieve the figure to be rotating in, altough if you concentrate hard enough, you can change the percieved direction, or it can happen spontaneously. Most people probably percieve the image to be moving counter-clockwise because of the position of her feet or arms, which make one direction look a little more natural than the other.
As for the whole “right brain vs. left brain” claim, there is no such thing as dominance of either hemisphere of the brain over the other. This is just a theory that has been invented to try to explain individual differences in language ability, creativity etc…, and has no empirical evidence at all. Both sides of the brain are responsible for all of these abilities to a degree. While we may differ in our abilities and personalities, we all use both sides of our brains equally.
This is similar to the “we only use 10% of our brains” “theory”, which is completely untrue. We absolutely use 100% of our brains, as MRIs would show. Have you ever heard of a person having a stroke and the doctor saying “oh not to worry, we only have tissue death in the 90% of the brain that the patient doesn’t use!”?
ca di
I was watching the star wars episode of family guy when i saw a similar illusion (the scene when they are looking at the Death Star Plans)
i made a more primitive version of this if you look at the small circle it rotates one way if you look at the big one it will rotate the other way but in reality they are just moving left and right and increasing/decreasing in scale.
http://www.glossygames.com/sphere.html
Gino
it’s counterclockwise for this reason: the shadow of the wide opened feet is always pointing into the screen/away from us. Assume you see clockwise, the time when she’s facing at you is the time when her toes are pointing away from us, that’s impossible, unless that’s not her shadow. In conclusion, if you are the people that see counterclockwise, try to cover her shadow and start imagining her being spinning clockwise (deceive your brain) then you’ll see what right brained people see.
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