15 October 2007

The spinning woman

A spinning dancer, from news.com, via Freakonomics and Marginal Revolution (I'm giving those sources because you might want to look at the comments there.)

There is a woman spinning; the question is, is she spinning clockwise or counterclockwise? Supposedly this has something to do with which side of the brain you use, although I'm not sure I buy it.

But my first thought was "clockwise from whose perspective? From the perspective of someone looking from above, or from below?" (To clarify what I mean by "clockwise", I mean that the dancer is turning to her own right.) I think this does say something about my brain, namely that I demand precise definitions for terms, at least for the sorts of terms that can have them.

Some of the commenters at various places say that you have to look at the shadow, because the shadow doesn't agree with the dancer; as far as I can tell this isn't true, and this is not some sort of optical illusion.

The actual resolution is that you can imagine reflecting the dancer through the plane of your monitor (I almost said "the plane of the board", because usually when I'm thinking about three-dimensional pictures it's when I'm teaching calculus), which will change the direction of rotation but not the picture. So on an intellectual level I understand why both perceptions must be possible. But I can't see her going counterclockwise. Not at all.

8 comments:

John Armstrong said...

It's very difficult to flip back and forth looking at the picture as a whole, beacause in either direction the raised leg leads.

Try covering all of the picture but the feet. Then try flipping them alone, before you uncover the rest of the image to find her spinning the other way. With some practice you can flip back and forth without much trouble at all.

Douglas said...

A tip from one of the comments on the freakonomics page: if you want to change the direction that the dancer is spinning, look away from her, hold up your finger and spin it in the direction you want her to turn, then look back.

Sometimes it doesn't work, say if you're really still looking at the dancer while you're pretending to yourself that you're looking at your finger, but that's the general idea.

Also works if you close your eyes, imagine the dancer spinning in our direction of choice, and then when you look again, that's the direction you see her spinning in. That's almost like The Secret!

fanfan said...

http://ofb.net/~whuang/imgs/spin/
can help you visualize both directions.

Blake Stacey said...

Steve Novella, a neurologist, has laid the smack down upon the left-brain, right-brain silliness connected to these optical illusions.

Michael Cassidy said...

It started out to be very hard to switch NOW its switching on its own.

I grabbed the image and move it in the direction I wanted it to switch: to the right counterclockwise; left clockwise.

John Armstrong said...

What's very hard to do is to see it as neither. This is something I started practicing with the Necker cube. That link shows the two most common interpretations, but can you force yourself to see it as simply a collection of lines on the plane?

Now try it with the dancer. Movement makes it a lot harder.

Brian said...

I had the same thought when I first saw it, "clockwise" relative to where?

This is an interesting illusion though. Usually on these sorts of "change point-of-view" illusions, once I do it once, I can "flip" at will. Even though I can "flip" this one, doing so remains difficult (at least without any of the "tricks" mentioned by other commenters).

unapologetic said...

A new variant. This one I can't flip at all, and I think everyone else would see him turning anticlockwise (from above) too. But I'm not sure why.