If clockwise, then you use more of the right side of the brain and vice versa.
Most of us would see the dancer turning anti-clockwise though you can try to focus and change the direction; see if you can do it.
This does really work. It is also possible to reverse the image(so I am told).
Please post what you see so we can get a rough idea of Sharenator users percentages.(look we are doing science, exciting isn't it?)
EDIT: Just found this gif which shows it both ways