Someone asked me this and I have pondered the same question for some time. I combed the net and came up with nothing. I don't even know what the concept is called or what it would fall under. I know the "illusion" only occurs at certain speeds sort of like resonant frequencies. It kills me riding home from class everyday and watching the tread run backwards (laughing at me) and I can't explain it. Someone put me out of my misery!