In view of feedback I've received, I feel obliged to make it clear that the demo presented in my offbeat article entitled Right brain versus left brain [display] is merely an amusing and innocuous hoax, which has nothing to do with the viewer's brain. My presentation of the demo and my subsequent comments were deliberately facetious: a big joke! It would have been neither more nor less silly to claim that viewers who see the girl spinning in a clockwise direction have right-wing political beliefs, and vice versa.
Only the final two sentences in my post [where I suggest that interested observers should examine the individual images in this animated GIF, using a graphics tool such as Fireworks] are to be taken seriously. The truth of the matter is that everybody sees exactly the same animation, which does indeed change directions suddenly, before reverting to the initial direction. The demo is ingenious in that the 34 fixed images composing the animation have been designed and drawn in an exceptionally skillful manner. Viewers are intrigued by the fact that, when the woman changes directions, she does so in such a smooth and seamless fashion that we have the impression that this change has taken place—like the perception of beauty—in "the eye of the beholder". This is an illusion. The change has well and truly occurred in the animation, not in our brains. In most of the silhouettes in the animation, various visual features of the woman—including her face, her breasts and her pony-tail hair—provide explicit clues as to the direction in which she is spinning. But I have extracted a unique image, shown here, in which all these visual features are missing:
Here, the viewer is unable to decide between two perfectly plausible possibilities:
— We are facing the silhouette of a woman poised on her left leg and spinning in a clockwise direction.
— The silhouette is a rear view of a woman poised on her right leg and spinning in an anticlockwise direction.
Consequently, when this pivotal image occurs in the animated sequence, the direction of spinning can be either maintained [as is usually the case] or reversed [exceptionally] in a totally seamless fashion. And this is why the woman seems to spin in a clockwise direction for a while, then suddenly change directions, and finally revert to the initial direction.
Some readers might not be familiar with the concept of animated GIFs. Back in the early Internet days, people often included an animated image of this kind in the email contact section of their rudimentary websites, showing a letter being folded, place in an envelope and slipped into a mailbox. Animated GIFs provide a good example of software gadgets—a little out of fashion nowadays—that are relatively laborious to create, but simple to borrow and use.