for me. it’s all about the arbitrary perception of which is the front leg and which is the back. I find if I scroll down so that only the feet are visible, I can control that perception pretty easily and switch back and forth at will. When I first looked at it, it was going counter-clockwise, I looked away for a second then looked back and it was going clockwise. It took some concentration to revere it again the first ime but once I figured ut what to focus on it became fairly effortless.
I am not that great with these, but for me the illusion works because it is a two-dimensional representation of a 3D event. Every argument about why she is rotating a particular way applies equally to either spin direction. Flattening the event to two dimensions makes it impossible to decide if her left leg is extended and she is spinning CCW or if her right leg is extended and she is spinning CW.
The shadow animation increases the perception that she is spinning–it gives more of a 3D perception to a flat outline–but it doesn’t help decide a direction. It’s also wrong b/c the extended leg shadow does not drop deeply enough into the picture. The light is coming from behind and above her. It is not coming from a super low angle since such an angle would elongate the thickness of the shadow axis foot, which is not much thicker than the dancer’s foot. The higher angle of the backlight should cause the spinning leg shadow to drop more deeply into the overall image when the spinning foot is away from the viewer’s perspective. I’m not sure if the incorrectness of the shadow is necessary for the illusion or just the casualness of the animation creator.
I have to pull out my Ouija board before I answer this. But seriously, this “scientific” personality study is all wet. I see clockwise and only clockwise. As such, the “study” says I am right-brained - classically the artsy type. Yeah, right…I can’t even draw a decent straight line with a ruler for carp sake! I am the classic left-brained person.
This study, however is neither right nor left-brained oriented…just plain feather-brained! 
Ah! I got it!!! It was the peripheral vision thing that finally made the switch possible. Now I can look at her, see her spinning CW, look away briefly and get her switched over to CCW. Whew! (I still can’t make her switch directions while looking directly at her, though).
Does it make a difference which hemisphere we’re in?
Try scrolling down so that she’s only visible from about mid-thigh down. Not only can she seem to be twirling, but (for me) she now mainly swings back and forth, all while facing me. Neat.
Started out counter-clock for me, but I can see either one at will.
ETA:
I remember reading that this sort of thing is important in golf while addressing the ball. One tends to be right or left eyed, and whichever is prominent should be downward of the other.
Well, either I’m the one being whooshed here, or you guys need to cut back on the acid, because it’s plain as day that the picture simply switches after a set time. Just watch it for 30 seconds or so. They purposely chose an image that’s distracting(woman) and hard to focus on, and notice that you only see a silhouette, which would make the transition seamless (if you could see any other details on the model, the change from clockwise to counterclockwise would be too obvious). If you look away for a moment and the direction changed, it just means the direction changed while you were looking away.
For those of you who claim you can “change it at will”, do you feel the same effect when looking at other spinning images?
:dubious:
I thought that the people that claimed she was spinning clockwise were just screwing with me, crazy, or delusional. I just got it to flip directions and now I can’t seem to change it back. Cool illusion.
I feel the same. How could she possibly be going in an anti-clockwise direction? Usually I’m decent at flipping these two-way illusions but this one I cannot budge it at all.
OK, I finally got it to switch, I had to shrink my browser to exclude the shadow and the upper body, and actually physically rotate my head in an anticlockwise direction (in the sagittal plane, not like The Exorcist), and then open the browser by degrees. Having done this, the image now looked like it had a really bad frame refresh rate, very choppy and difficult to focus on. Once her full body was in view I could not hold it to anti-clockwise for more than a few seconds, it snapped back instantly. If this is true I must be one of the most hardcore right-brain people around.
I’m afraid that your brain is playing tricks on you :). Download the gif and open it in a program that can handle multilayer gifs. You will find that it is a multilayer gif with 34 layers. The layers depict exactly one rotation.
Yeah, but in what direction?
Let’s break down the OP. I see it as two questions:[ol][]Is there any relationship between how we view the animation rotation and a connection to right- or left-brain oriented individuals, and []Is there any connection between certain human talents/abilities and the side of the brain that controls them, independent of social factors?[/ol]
Ah, I was going to to that. Thanks for saving me the time 
When I first looked at it, she was clearly going CCW, and didn’t change no matter how long I looked, whether I looked with only one eye or the other, whether or not I squinted, etc. CCW, CCW, CCW … until I started reading the text on the left. Then she abruptly switched to CW, in the corner of my vision, and when I looked straight at her again, she continued CW. Then I stared a while longer and eventually she seemed to be going CCW again.
That’s a really left brained way to solve this problem. I would’ve suggested bringing someone else into the room and seeing if they see reversals at the same time.
Wait, it just switched on me. Your way is better.
The best way to prove to yourself you are not being whooshed is to ignore the perception of rotation and simply consider the fact that a silhouette, because it reduces three dimensions to two, will look identical with either direction of rotation. It is not spinning at all. It is just flopping back and forth. The animation is built by combining individual stills, obviously. You could not look at a single still and perceive CW or CCW. That is why no argument about how she “must” be spinning in a particular direction is valid: what the shape itself is really doing is changing in two dimensions (up-down/left-right). All perceived movement in a front-back dimension is added by the brain. In the silhouette itself nothing is moving in that dimension. The shadow adds to the illusion that there is depth, but of course there is none.
Also, consider that since it’s a silhouette, when it is facing directly towards you or away from you, it looks the same. There’s no way to determine if it is facing towards you or away. So, when it is facing to the right, either it was facing away and will be facing towards you, in which case it is turning clockwise, or it was facing towards you and will be facing away, in which case it is turning counterclockwise.
This is also related to which of her legs is raised. When she’s facing away, it’s her right leg, when she’s facing towards you, it’s her left leg. But since you can’t know which way she’s facing, you can’t tell which leg it is, so it can seem to switch.
Try looking at it in Firefox and IE at the same time. My IE image is much slower, and I can get CW on one and CCW on the other. Or both the same.
Holy crap I’ve got Opera, too. It’s slow in Opera, as well. Three images rotating at different speeds and directions, changing directions at a moment’s notice. Thank you, SDMB.
It may appear that way, but it’s just your perception that’s flipping, not the image itself. If you concentrate, and practice for a bit, you should be able to get it to change a lot more often than every 30 seconds or so[sup]1[/sup].
Interestingly, what appears “plain as day” in this kind of perceptual illusion is often not plain at all. Remember, your brain’s visual processing systems are creating the illusion of a rotating 3-dimensional object from a flat silhouette image that essentially just slides a bunch of black pixels back and forth.
[sup]1[/sup]Though I understand there are a lot of people who have trouble doing this kind of “Necker transformation” at all – I wonder if they’re the same people who have trouble seeing those 3D “Magic Eye” stereograms?
Whether people can see it go one direction or the other is neither here nor there. The question in my mind is does it really indicate you’re “left brained” or “right brained” as per their list?
And I say no, they’re completely wrong.