Anti clockwise for me at first but if i look away for a second she changes, sometimes it takes a couple of goes of looking away before she changes direction.
Same with Berts ball.
Thanks guys, I really enjoy that kind of stuff.
If your brain is normal you should see reversals in direction even though both gifs just run in the usual way. The interval time will vary from person to person.
What is happening is that your left and right brain hemispheres take turns in being dominant.
Here is another from Jack Pettigrews site. Would you believe both grey surfaces have the same brightness! Check it by covering everything apart from the surfaces.
I can perceive the lady spinning counter clockwise if I use averted vision. Should I bring my direct attention to the image it then, apart from the odd occasion of holding for a couple of rotations, reverts to clockwise.
Bert's sphere I can 'command' my senses to believe either direction and even the 'folding in' apparition. Perhaps this is why I, like others on this site, have trouble sorting 'domes' from 'craters' in moon images.
We have evolved where the illumination comes from above ie Sun and sky. Your experience and memory tell you that a surface facing up is better illuminated than a surface facing down. Hence when presented with two surfaces that are of equal brightness your brain automatically compensates and assesses the upper surface as being darker.
Seeing is not believing!
I have inverted the image. There is still some background effect (thats another story) but note they look more similar in brightness.
Try cropping to get rid of the background. This also affects our perceptions.
The intensity gradients at the center boundary also have an effect as they also give a visual cue to where the illumination is coming from.
Well I found this interesting, I did an experiment with my son and asked him which way my hot babe was spinning and it seemed that at times she would slightly slow down and that's when she changed direction for the both of us!
Classic, Daniel 
