Ballerina illusion

[Oniya]

http://www.procreo.jp/labo/labo13.html

Mr. Oniya happened to have a web page up with one of those 'intelligence test' scams on it - you know, the ones where you go through a bunch of different questions, and then it asks you for a cell phone number so it can text you the results (and sign you up for a $9.95 monthly charge for text spam).  The link above does not go to that site, but to the site of the guy that invented the illusion.

The question is: does the ballerina spin to the right (with the foot crossing from left to right as she faces you) or to the left (with the foot crossing from right to left as she faces you), or does she appear to reverse directions (randomly, or through your own conscious effort)?

[Will]

It spun to the right for me, initially.  I was only able to make it switch directions by trying really hard, and then only by focusing on the figure's feet. 

[Trieste]

She goes from one to the other pretty easily for me, although it's slightly harder for me to make her go from spinning counterclockwise to clockwise than it is to make her go from clockwise to counterclockwise.

In the past, when I first ran into this, I noticed that - on discussing it with friends - everyone (or everyone who can make her reverse direction; for some people she goes the same way no matter what) seems to have one point that they can stare at that makes it easy to switch from one to the other. And, strangely, the points are different. One person had to look at her head, one had to look at her foot...

[Oniya]

With me, it was pretty easy to make her switch - she'd even switch randomly before I started to try 'controlling' the spin.  Mr. Oniya wasn't able to see the switch until the little Oni came downstairs and said 'Oh, she's spinning [the other way].'  This was despite the fact that I tried to convince him that it was even possible to switch it for a good ten minutes.  The spam-quiz was trying to associate it with whether one was right-brained or left-brained.

[Trieste]

I'm ambidextrous. I write with my left hand almost exclusively, but a lot of other things I do with either hand, depending on whatever's easier. She switches randomly for me, too, and sometimes I'll get points where I can see both perspectives. It's like she's spinning both ways.

But it's my experience that even folks who seem very right or left brained can get her to switch, so.

[Oniya]

I joke that I write equally legibly with both hands, but that's really because I write equally illegibly with both hands.  Playing piano and guitar might compensate as far as left/right motor skill balance goes, though, and I do have the combo of analytical and creative going (the classic 'left-brain'/'right-brain' assignments).  It may be that people who are more evenly 'brained' get the random switching, but since no one is exclusively one or the other, the switching can be accomplished with the right sort of effort.

[Lilias]

It always spins counterclockwise for me, although my righthandedness fluctuates. There are days when I feel like doing extra things left-handed, and others when I can't drink a glass of water like that. Interestingly, my typing is balanced, even with the left hand going a bit easier, but I don't have any other two-handed activities to compare.

[jouzinka]

She alway spins with her foot from (my) right to left and I can't get her to turn no matter what. :(

[Hemingway]

I can't get her to spin any way but clockwise. My brain sucks.

[Tabbi]

I have heard that if you focus on such things as math, she spins one way, and focusing upon art makes her spin another. It works for me, when looking at only one part of her body does not.

[Neroon]

She only ever swings the one way for me., clockwise.

[DarklingAlice]

This has nothing to do with left-brainedness vs. right-brainedness. Rather it is a weakness of our inability to hold simultaneous multiple worldviews, regardless that those views are equally valid. Another classic example of this phenomenon is the Necker Cube.

[jouzinka]

I can see the cube from both top and bottom. But the ballerina just wouldn't change her rotation! >:)

[DarklingAlice]

The ballerina is an imperfect example of the phenomenon. The majority of people see her spin clockwise, and once she is seen to spin clockwise she is more difficult to reverse. Thus it is not a neutral image like the Necker Cube.

Interestingly, the bias is apparently not a bias towards seeing clockwise motion, but rather a bias to assuming that we are looking at her from above. Probably a result of the upright posture that characterises our species.

[jouzinka]

Did it. TWICE. Ha!

But once I see her turning one or the other way, it's pretty hard to change for the other.

[Trieste]

She goes from one to the other pretty easily for me, although it's slightly harder for me to make her go from spinning counterclockwise to clockwise than it is to make her go from clockwise to counterclockwise.

The ballerina is an imperfect example of the phenomenon. The majority of people see her spin clockwise, and once she is seen to spin clockwise she is more difficult to reverse. Thus it is not a neutral image like the Necker Cube.

Interestingly, the bias is apparently not a bias towards seeing clockwise motion, but rather a bias to assuming that we are looking at her from above. Probably a result of the upright posture that characterises our species.

God, always with the short jokes with you. :P

[Oniya]

The Necker Cube is much easier for me to switch, to the point where I can pick a corner and 'pull' it to the front.

Interestingly, the bias is apparently not a bias towards seeing clockwise motion, but rather a bias to assuming that we are looking at her from above. Probably a result of the upright posture that characterises our species.

Above?  I see her as standing on level with my view-point.  Above would be much less ambiguous.

[DarklingAlice]

From Wikipedia:

These results can be explained by a psychological study providing evidence for a viewing-from-above bias that influences observers` perceptions of the silhouette [6]. Kayahara`s dancer is presented with a camera elevation slightly above the horizontal plane. Consequently, the dancer may also be seen from above or below in addition to spinning clockwise or counter-clockwise, and facing toward or away from the observer. Upon inspection, one may notice that in Kayahara`s original illusion, seeing the dancer spin clockwise is paired with constantly holding an elevated viewpoint and seeing the dancer from above. The opposite is also true, an observer maintaining a counter-clockwise percept has assumed a viewpoint below the dancer. If observers report perceiving Kayahara`s original silhouette as spinning clockwise more often than counter-clockwise, there are two chief possibilities. They may have a bias to see it spinning clockwise, or they may have a bias to assume a viewpoint from above. To tease these two apart, the researchers created their own versions of Kayahara`s silhouette illusion by recreating the dancer and varying the camera elevations. This allowed for clockwise/from-above (like Kayahara`s original) and clockwise/from-below pairings. The results indicated that there was no clockwise bias, but rather viewing-from-above bias. Furthermore, this bias was dependent upon camera elevation. In other words, the greater the camera elevation, the more often an observer saw the dancer from above.

The source they use in .pdf format.

And this passage from the source paper might explain why focusing on specific parts of the image helps the shift:

Last but not least, we should say that Kayahara’s original silhouette is in fact a much richer
stimulus than it seems. Being a silhouette it is depth-ambiguous because it lacks any cues
from self-occlusion. On the other hand, it does contain two subtle depth cues—however,
with conflicting information. Tracing the end of the outstretched hand shows that the camera
elevation with respect to the hand is only 6.0 deg, which is a little less than the value for
the foot. That means that the figure was rendered with a perspective camera positioned
about 75 meters away from the figure (assuming a vertical distance of 1 m between foot and
hand). According to this perspective cue, the view from above and therefore the clockwise
rotation is the ‘true’ rotation. However, another cue to the rotation of the figure is provided
by the shadow the feet cast on the ground. The ellipse circumscribed by the shadow of the
outstretched foot—at least assuming that the ground is horizontal and that we are looking at
it from above—clearly suggests counter-clockwise rotation. There are good reasons for the
appeal that Kayahara’s silhouette figure has experienced in the media.

God, always with the short jokes with you. :P

Snrk.

Above?  I see her as standing on level with my view-point.  Above would be much less ambiguous.

This is why it is easier for you to make the switch. As I say, it is a predisposition in ~2/3 of the society to jump on the visual cue indicating that the camera is located above her. Certain individuals will have their own visual quirks.

[EuroLover]

I find it very easy to change the way she spins. I just have to look at her feet and then I can change her rotation consciously, whenever and how many times I want.

If I just look at it, she's usually spinning counterclockwise.

[Drow Denizen]

For those having trouble visualizing the reversal of direction.

[Oniya]

Oddly enough, if I look at the center one, all three seem to move in the same direction - which I can either switch by my normal method, or by focusing briefly on the right or left dancers.

EDIT:  Oh, and the glowing white eyes are very creepy, thx.

[Jag]

EDIT:  Oh, and the glowing white eyes are very creepy, thx.

Did not notice those till you pointed them out. Thanks, Oniya. They will haunt my dreams tonight. :P

[Oniya]

You obviously don't frequent Sabby's dream thread.  :P

[Jag]

Nope, I don't. :P

[Drow Denizen]

*Hums 'Turnaround, bright eyes..'*  :o