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April 03, 2009 12:30 AM
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The best explanation I can find is this one by Steven Novella, from the NeuroLogica Blog:
"The spinning girl is a form of the more general spinning silhouette illusion. The image is not objectively “spinning” in one direction or the other. It is a two-dimensional image that is simply shifting back and forth. But our brains did not evolve to interpret two-dimensional representations of the world but the actual three-dimensional world. So our visual processing assumes we are looking at a 3-D image and is uses clues to interpret it as such. Or, without adequate clues it may just arbitrarily decide a best fit - spinning clockwise or counterclockwise. And once this fit is chosen, the illusion is complete - we see a 3-D spinning image."
Claims that this image determines whether a person is right-brained or left brained are inaccurate.
I can generally only see this image as rotating counter-clockwise, but if I spend a lot of time on it, I can eventually get it to shift. I don't know what this says about me, if anything.
Source(s):
http://www.theness.com/neurologicablog/index.php?p=27
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I think the reason is that since it is a silhouette you have no depth perception. Because of this you can't tell if a body part is close to you or far away.
Also since when the body parts overlap, there are no borders. So you can't tell if the arm is going in front of or behind the body. Same thing with the legs.
I still can't quite wrap my mind around it. I downloaded it and played it in WMP, and I sat there for like five minutes starting and stopping it.
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This appears to be one of the better/best answers. http://www.news.com.au/perthnow/story/0,21598,22492511-5005375,00.html
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I can see her turn both ways, CW and CCW, and I can "flip" from one mode to another fairly easily, by staring at her feet, slightly de-focused.
There is no trick in the animation itself, it's your mind that "sees" the girl turning one way, or another, just as Demanda suggested. I have opened the file in a gif animator (type of program), and have reversed the frame order, which in effect reverses direction of (apparent) motion... and guess what? - it makes no difference, can't tell them apart, can you?
It is true that some people perceive the motion by default as being CW, while others see her turning CCW. It is less clear why is it so. The animation is certainly not a simple left- / right-brainness "test", but I think it has something to do with what Steven Novella calls "hemispheric dominance". I also think that he downplays the importance of this asymmetry, not in his analysis of the animation, but more generally speaking - he seems to be confusing brain/ mind as such with our current understanding of it.
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What is the most correct explanation for the spinning sillouette effect?
At first, the girl seems to spin clockwise (if you watch from above) but after some time, she spins in the opposite direction. Or doesn't she? 
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| April 03, 2009 12:54 AM |
"The spinning girl is a form of the more general spinning silhouette illusion. The image is not objectively “spinning” in one direction or the other. It is a two-dimensional image that is simply shifting back and forth. But our brains did not evolve to interpret two-dimensional representations of the world but the actual three-dimensional world. So our visual processing assumes we are looking at a 3-D image and is uses clues to interpret it as such. Or, without adequate clues it may just arbitrarily decide a best fit - spinning clockwise or counterclockwise. And once this fit is chosen, the illusion is complete - we see a 3-D spinning image."
Claims that this image determines whether a person is right-brained or left brained are inaccurate.
I can generally only see this image as rotating counter-clockwise, but if I spend a lot of time on it, I can eventually get it to shift. I don't know what this says about me, if anything.
Source(s):
http://www.theness.com/neurologicablog/index.php?p=27
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Other Answers (3)
April 03, 2009 12:53 AM
Wow that is cool. I think the reason is that since it is a silhouette you have no depth perception. Because of this you can't tell if a body part is close to you or far away.
Also since when the body parts overlap, there are no borders. So you can't tell if the arm is going in front of or behind the body. Same thing with the legs.
I still can't quite wrap my mind around it. I downloaded it and played it in WMP, and I sat there for like five minutes starting and stopping it.
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April 03, 2009 01:54 AM
Nope, Tried blinking and staring unfocused. Cannot get it to spin CCW.
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April 03, 2009 02:21 AM
Yea I have seen her spin both ways. If you cover up everything but the feet I think its easier to get it to change directions.
I'm skeptical about the whole right brain vs. left brain thing, but I guess its possible.
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I'm skeptical about the whole right brain vs. left brain thing, but I guess its possible.
April 03, 2009 01:04 AM
I've posted this many times on a number of sites, here you'll see a lot of comments about it. http://www.mobog.com/p/SmokenHerb2/11fuukq This appears to be one of the better/best answers. http://www.news.com.au/perthnow/story/0,21598,22492511-5005375,00.html
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April 03, 2009 10:47 PM
Nice one, Nushka! This animation is featured, in a slightly different context, on my own website for some time now... I can see her turn both ways, CW and CCW, and I can "flip" from one mode to another fairly easily, by staring at her feet, slightly de-focused.
There is no trick in the animation itself, it's your mind that "sees" the girl turning one way, or another, just as Demanda suggested. I have opened the file in a gif animator (type of program), and have reversed the frame order, which in effect reverses direction of (apparent) motion... and guess what? - it makes no difference, can't tell them apart, can you?
It is true that some people perceive the motion by default as being CW, while others see her turning CCW. It is less clear why is it so. The animation is certainly not a simple left- / right-brainness "test", but I think it has something to do with what Steven Novella calls "hemispheric dominance". I also think that he downplays the importance of this asymmetry, not in his analysis of the animation, but more generally speaking - he seems to be confusing brain/ mind as such with our current understanding of it.
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Now I don't think it is flipping because you can actually see the half angles. Try blinking more often and you will see it, the brain is not completing those images, they are real. However, the frames could be less than we believe they are.
A more accurate explanation via a comment on that page:
The image does change with each rotational position around 360 degrees. I.e., if the animation frame rate is one frame per degree of rotation (for example), there are 360 unique frames total in the animation. One way to tell this is to look at her shadow, which is different between the “front” 180 degrees and the “back” 180 degrees.
Also, this offers a good visual analysis:
http://www.randominc.net/spinninglady/
The comment you cite is much better, thank you for going further.