Looks to me like the spinning girl actually does change direction although I don't know how much or what parts of the actual animation file change. I don't see how the apparent lead with the left (and then the right) arm could be illusory.
and its use as a study of schizophrenia.
there is also a cool study of the brain that showed that schizo is actually just the fact that some folks brains don't have the half second delay that everyone else has.
was written up along with the study of the fake hand being touched.
there is also a japanese researcher that claims that ALL the opticlal illusions are the brain trying to locate the parallax of the "end" of the illusion to judge distance.
some cool studies on computer screen opticals that show directional changes from font sizes stacked in interesting ways.