I read through the 620-some comments at that Left/Right Hemisphere Test.

As I mentioned, the comments are as fascinating as the test itself. I didn't take notes, but my impression is that many people who initially see the figure rotating clockwise are unable to see it any other way. Others initially see it one way - most often CCW, I'd say, and by hook or crook eventually see it going the other way. (See my post "It all depends" in this thread.) Some are quite sure that the whole thing is a fraud, and the animation simply reverses direction intermittently. Others note that two people watching simultaneously often see the figure rotating in opposite directions, and that effectively rules out fraud, a fact which I'd pretty much established to my own satisfaction independently. A few simply see the figure going back and forth, that is, not rotating at all. A very few asked what seems to me an obvious question: what is the frame or point of reference to determine direction of rotation? A very good question, I'd say, and one I hinted at in my "BTW" post in this thread, and expanded on at the conclusion to my "...depends" post.

Besides the interesting points of view, one poster pointed me at Perceptual Rivalry and Reversible Figures from the Univ. of Queensland in Oz, which explores a number of such visual paradoxes. Jack Pettigrew is the page's author.

From there, I found the designer of the original animation, a fellow by the name of Nobuyuki Kayahara, whom, I suppose it could be said, I have plagiarized. Later, I may take a crack at translating some of his web page.

I haven't done much more at Pettigrew's page than take a quick peek and link it here. Serendipity, indeed!

I addition, I found this article, Bring On the Dancing Girl from the 10-12-2007 issue of New Scientist. The article claims "What this animation does not involve is different sides of the brain, as the initial post claims. What you see is purely due to your perceptual and cognitive flexibility."

Ah, so. Well, I'd say the good doctor from Down Under might beg to differ, and the plot thickens. Stay tuned.

S