We expect to see that first in the illusion. The problem is we find nothing in the illusion that will confirm our expectations. The brain then searches for clues by switching things around, at least for a while.

Most people are right handed (or footed in this case) and that lends itself to a rotation bias. This is reflected in the sport in which we see rotation the most, figure skating. “Clockwise” and “conterclockwise” rotations are not equally likely in real life, and evaluating this as a purely visual bias would have to take this into account.

With the spinning dancer illusion above, my hack is to look at the shadow foot when I want the direction to change from clockwise to counter-clockwise.

Good of Dr. Novella to explicate that this illusion has no utility in determining brain hemisphere dominance

That is barely believable.

Back when I studied psychology, psychology of perception was easily the most interesting module and illusions, especially their worth (or lack thereof) in studying perceptual phenomenon, were of great interest to me too. I think the most interesting thing that perceptual illusions do is show us how our underlying visual heuristics work, as Novella touched upon in the article. Beyond that they’re pretty worthless since they’re just too divorced from real world perceptual experience to be ecologically valid for anything. Sadly these ‘test your IQ by seeing how many circles rotate!’ illusion-based hoaxes are endemic online.

Anyway, read dancing is more fun if there are real naked people.