My mom sent this to me today.
When you click on the link, you'll see the woman in silhouette to the left, only she'll be in motion. But the direction in which she'll be turning (clockwise or counter-clockwise) will depend on which hemisphere of your brain is dominant.
I won't say in the post (though I will in the comments) which direction she turned for me, but I will say that when I'm watching it, I have a very hard time figuring how anyone could possibly see her spinning in the opposite direction.
A couple of hours ago, however, I did see her turning in the opposite direction, but just as soon as I'd perceived it, she started turning the way she always turns.
Anyway, pretty interesting.