A form of apparent movement, indistinguishable from real movement, that occurs when two visual stimuli a few centimetres apart are presented in an alternating pattern with an interstimulus interval too long for the stimuli to appear simultaneous or for partial movement to occur but not long enough for phi movement or the disappearance of apparent movement and the veridical perception of the stimuli simply alternating. In optimal movement, a single stimulus appears to move smoothly and continuously back and forth across the space between the two actual stimuli. Also called beta movement, stroboscopic movement, or optimal motion. Often misleadingly called the phi phenomenon, a term that in careful usage is reserved for the phenomenon of phi movement. See also Korte's laws.