This is really cool. Stare at it for a while and you should be able figure out why (no, it's not because her nipples are inexplicably fully rendered).
Explanation and a neat trick after the jump.
The image is an optical illusion. The girl appears to be spinning in one direction when you first look at the image, but after a while she appears to switch directions.
The great thing is, you can actually make her switch directions in your mind at will. The trick, at least for me, is to focus on the leg that's raised off the ground. Think of it as the girl's right leg to make her spin clockwise, and as her left leg to make her spin counterclockwise. You could also focus on the bent arm or the hip of the raised leg to make this happen, but I prefer, for reasons I don't think I need to explain, to focus on the leg. If you get good at it you can actually convince yourself that she's just swinging back and forth, and not spinning at all.
Also, she appears to spin faster on Firefox than IE, which makes it harder to control her direction. If you download the image and open it in an image viewer that can read animated GIFs you should get the slowed-down version.
Science!
EDIT: Here's a visual aid.
Unaltered frame:
Frame with raised leg pictured as right leg:
Frame with raised leg pictured as left leg:
The black is the same in all three pictures.
She has a propensity to turn clockwise (viewed from above) for me, but I've gotten myself to the point where I can cross my eyes for a moment to force the switch. I can't make the switch happen at will without some intermediary vision state, like crossing my eyes.
She's all clockwise for me, all the time.
Yeah, I'm with Dianna. I stared at it for 5 minutes and all I got was a headache. This is as bad as a Magic Eye poster.
No, it's worse. Magic Eye posters have the courtesy to stay still whie you're trying to look at them.
Gah! There it goes! Clockwise, then counter-clockwise! If I scroll down the page until all I can see is her feet, right before she disappears off the top of the page I see her change direction. Then when I go back she's going the new way.
Good show, sir. I take it all back.
Bully!
Also, not all stereograms stay still.
THAT is the single most amazing thing I have ever seen. I now know what I'm going to be watching for the next three hours while I wait for FedEx.
are you sure she's not actually switching directions?
does that shark have way too many fins and flippers or is it just me?
also i can see the girl going both ways but i don't think my brain is making me see it so much as she's just actually changing directions. my head hurts.
Okay, here's the big secret about twirl girl. Basically, the animation is like those old catfood commercials where they made the cats "dance" by looping the tape back and forth. When the raised toes get all the way to one side, the animation just plays backwards until the toes get to the other side, and then it plays forward again and so on. But your brain fools you into thinking she's spinning.
If you open up the image in Photoshop, where you can see each frame as a separate layer, you'll see what I mean.
Open two windows with the same image and try to picture them spinning opposite ways. I have trouble switching back and forth easily between both directions. It takes me like 15 seconds and a good effort. I'm much better with the old and young woman. I wonder what this says about me.
She was only spinning clockwise for me, but as I scrolled down to read what you wrote, she started spinning the other way. I pretty much have to look at the bottom quarter only if I want her to go counter-clockwise, but once my brain latches onto that, she keeps spinning that way.
That's freaky!
When I first glanced at her her, I thought it was clockwise, then after a couple of seconds she jumped to anti-clockwise and I couldn't get her back no matter how hard I tried. For me, blinking hard or crossing eyes works best - just looking at the feet only eventually works but takes a while.
But I wanted to ask - for those of you who were stuck on clockwise, would you agree with the summary of the right-brain description of yourselves?
We had a huuuge fight with my boyfriend last night over this image!!! : )
He was able to switch like in no tiime but I just couldn't!!! no matter how hard I tried or how long I stared; nope! I just couldn't and I freaked out and asked him to help me out and he rubbed it on my face ( and I got this image with a letter saying if you can see it both ways your IQ is like over 160 something something...) and with all that anxiety I fell asleep thinking of the image.
but now; thanks to you guys comments, i actually see it both ways... i'm not still able to switch back and forth i could see her twirling other way ( which is counterclockwise for me ) only when i'm interested in something else like reading or looking at some other thing on the page... meaning not actively looking at the image...
I think that has got to tell us something about us or the way we see or how we think... cause "seeing it only when you look at the other way" is totally creepy...
am i trying to hard to see? or this directions can actually mean something???
fighting the law is cool but i need explanations : )
Thanks again for helping me out of this idea that i'm blind to counterclockwise : )
o:
i want to be a twirl girl but i dont know how to be
Can we assume that in the original photo shoot of this girl, she was in fact twirling? If so, is there some way to tell in which direction she actually was spinning?