Fig. 4.

An apparent motion stimulus configuration for inducing pattern formation. A square is defined by the illusory movement of 20 icons. If, for example, every fourth icon is lit and then extinguished followed by the icons clockwise to them, and so on, the percept is of five icons moving clockwise around an imaginary square. If the room lights are extinguished, the interior of the square fills with illusory colored textures (generally smoky or taffy-like) and a five-bladed fan appears and rotates in time with the icons. Additional blades can appear fleetingly if visual persistence leaves some extinguished icons visible (depicted here as filled gray squares). Active icons are shown here as filled white squares; inactive icons are depicted as black squares with a broken white outline.