Another interesting optical illusion effect. Looking at this image you may very well see a scintillating effect along the light grey rivers. Presenting the illusion of movement along those paths.
Update:© 1998, Sarcone and Waeber
Update: When I posted this image I had no idea where it originated. Since then I found that this image is copyright 1998, by Gianni A. Sarcone and Marie J. Waeber, co-founders of Archimedes' Laboratory.