The pixel arrays are refreshing randomly. There is no coherence from frame to frame.
Any coherent motion you see (for example, up and down, or side to side, or rotating around) is constructed in entirely your mind.
I will be presenting some empirical studies about The suggestible nature of apparent motion perception at the Cognitive Science meeting this July in Pasadena.
A 1-minute video about Mind-controlled-motion was selected as a Top-10 finalist in 2015's Best Illusion of the Year Contest.