I wonder if it would work in real life, with a grid on a spinning piece of paper...

To me, it seems like the brain is breaking up the image into sections, and processing them separately, and then knitting them back together. The sections are slightly rounded and seem to move about.

I can even control the sections consciously, so some extent, as I can when I watch the swirls that you get on a untuned TV. But that would probably give me a migraine if I did it for too long.

If you just let your mind do its magic, without control, I bet it could actually help get rid of a migraine...