Look at this image. Do you see the dancer turning clockwise or counter clockwise?

If you see it spinning clockwise you apparently use your right side of the brain, if you see it spinning counter-clockwise you use your left side of your brain.

Source and explains the functions of the two sides of the brain.

-edit-
are you using, I hate not being able to edit thread titles.

I see it going clockwise which makes sense since I'm left handed. The article says if you focus you can see it spinning the opposite direction but I can't (and I can even see magic eyes with ease).

Just had this go through my work. Most people were clockwise - I definitely was. But if you focus on the feet alone (and allow your focus to go under the image) it can look anti-clockwise.

Looks to me like it was rendered out as a clockwise animation rotation.

how can anyone see that as clockwise? use the top of her head as the middle of a clock she is turning the opposite direction as a clock would, counter clockwise

i see it going counter clockwise. i tried focusing hard to make it go clockwise but then i saw the nipples..... why the hell dos it have nipples?! >.

no it dosent, they say if you see it moving clockwise you are more right brain orientated therefore you prob should be right handed.

im left handed and see it as moving anti clockwise, plus those atrributes they list as left brain dominant apply alot to me.  

She be moving clockwise in my eyes. I cant see how any one can see her spinning counter-clockwise

Counterclockwise first, then clockwise after scrolling down and back up, then counterclockwise again XD

Mostly counterclockwise though, makes sense since I am a very logical person

Edit: Woah clockwise again, this is just creepy. Does it mean I use both sides of my brain equally? 

i got it! just focus on her heel when she touches the ground it goes clockwise, when shes at her peak it goes counterclockwise. its pretty easy ^^ .her feet just does a 180 degree turn, her back turning towards us, only the top confuses our heads, so dont mind the top, just focus on the feet and turn it. after the feet goes on the direction you desire you can look at the top again and see the results.