A disk was divided into 16 stationary sectors of different grey levels that stepped around clockwise.When thin stationary spokes of constant mid-grey separated the Fan Grill sectors, the spokes showed robust and striking counterclockwise apparent motion, and when stopped, they gave a brisk clockwise motion aftereffect.The spokes had to match AEG KDK911423M SOUS VIDE INTEGRATED VACUUM SEALING DRAWER BLACK GLASS/STAINLESS the grey of some of the sectors.
We attribute these effects to small displacements across the thickness of the spokes that stimulated hard-wired motion detectors.