A belongingness principle of motion perception.

Four experiments are reported that investigated the role of the perceived coplanarity of a moving target with respect to a frame of reference in the third dimension on the perceived path of that target. When a target dot and small moving frame appeared coplanar, the dot's perceived trajectory was governed entirely by its changing position relative to the moving frame. However, when the target and a large stationary frame appeared in a different plane than the small moving frame, the motion of the dot was seen independently of the moving frame. The results support a belongingness principle of motion perception: The displacement of an object relative to a frame of reference to which it belongs governs its perceived path of motion.