I believe this is the original source of the image. http://www.procreo.jp/labo/labo13.html The author says nothing beyond it being a mysterious illusion.
The switching is as arbitrary as the coriolis effect. Try this thought experiment. Imagine instead of a woman, there was a perfect, black, sphere in the image. You couldn't tell if it was rotating at all. Now I add a protrusion to the "equator." Its length would vary in a sinusoidal fashion, and you could guess the ball is rotating, but still cannot reason it's direction. I can then successfully add protrusions such that it looks like a human and you wouldn't be able to tell; it's a simple lack of visual cues.
edit: my bad, not the coriolis effect. I was referring to the toilet-draining direction that is incorrectly attributed to the effect. The point is, given a little push in one direction, the water, or the image, would continue to rotate in that direction.
But there is absolutely no conclusive evidence to suggest this is true, and to show these kinds of things on The Daily Telegraph is a pretty big disservice to teaching people about neuroscience, I think.
This doesn't mean there aren't differences in the hemispheres, but just that visual tricks like this are probably not accurate at all for determining hemisphere dominance (if such a thing exists).
Nerves of each eye are wired to both left and right brains. Hence there is no order of processing information based on which field of view it is presented in.
Curious discussion about hemispheric dominance; I never really thought about it. I guess a better term is "lateralization."
It's completely random, and has nothing to do with left or right brain dominance; it's even easy to force it to switch to the other direction.
We all 'know' that left-handers use their right brain and right-handers use their left brain. In one library book about handedness, the author had found studies about which parts of the brain are used by two groups of people, one left-handed and one right-handed.
For right-handers, it was about 95% left-brain, and 5% right-brain. However, for left-handers, there were three possibilities. It was about 60-65% right-brain, 20-30% left-brain, and the cortex for 5 or 10% of them.
I don't remember what they were measuring, but a third option for left-handers is interesting in itself. (It may have been a study about which eye is dominant based on what a left-hander would say, so those for whom the cortex functioned in a different way were grouped with left-handers?)
Another book says that in those people who 'hook' their wrist when they write (so their hand is actually lower than their wrist), they do it subconsciously because their wrong brain is being used. They are NOT meant to be using that hand as their brain is struggling to use the correct brain. So, if you're right-handed, and you hook, you might actually be right-brained and left-handed. And, if you're 'left-handed' but you hook when you write, you're actually a righty.
I thought about this a bit and noticed that with about 10% of people self-identifying as left-handed, the stats above might fit. If 3-5 percent of right-handers use their right-brain, maybe they 'hook' and are in fact natural left-handers ('fake righties'). And if 20-30% of left-handers are actually left-brained, then that's a few percent of the overall population who are actually right-handed ('fake lefties'). Those could also be 'hookers' who aren't actually using their natural hand.
A. Covering almost all the image and focusing only in the lower feet.
- or -
B. Closing your eyes and trying to picture it rotating in the opposite direction. And then opening your eyes.
