This optical illusion is pretty amazing. According to the article, if you see the girl spinning clockwise, that means you're using the right side, or more creative side, of your brain. If she appears to be moving counter-clockwise, then that means the left side, or more logical side of your brain, is dominant.
What the article doesn't say is that if you focus on where her legs pass each other and visualize the elevated limb passing in front of the other when it appears to be passing behind it you can actually get her to switch directions. I guess this means that your brain is switching hemispheres.
Of course, you have to ignore the fact that the young lady appears to be in her altogether to get the illusion to work at all.RLC