Targets were displaced to cancel an apparent displacement induced by a step motion of a background or were held stationary while appearing to jump in an induced displacement. Target and background were then extinguished, and the subject pointed to the target’s last position. When the target had appeared to move but did not, background position did not significantly affect pointing; when the target had moved but appeared to remain stationary (displacement canceled by opposite induced displacement}, pointing depended upon the target’s egocentric position. A similar result was obtained with sinusoidal motion. In terms of a two visual-systems hypothesis, the motor system uses more veridical spatial information and is less affected by relative changes in two retinal signals than is the cognitive system. An increase in threshold for detecting target dis- orientation was accurate and identical under the two placements during saccadic eye movements is nowconditions. Failure to detect a displacement had no well established. First described qualitatively byeffect on the accuracy of pointing to the target’s Ditchburn (1955) and by Wallach and Lewis (1965) new position. Control experiments showed that the and rediscovered independently by Brune and LiJckingeffect could not be explained by criterion effects. The (1969), the effect has been analyzed more recently byresult was interpreted in terms of the "two visual

Induced movement, illusory movement in a stationary stimulus resulting from adjoining movement, has received steady experimental investigation over the last 70 years or so. It is observed under different viewing conditions in a wide variety of displays that differ considerably in overall size and in form of inducing and induced stimuli. Explanations have been diverse, some being based on relations within the display and others invoking mediation by other aspects of the observer's perception. Probably, no one explanation can account for all forms of induced movement. Current knowledge about induced movement may have important implications for visual perception of object morion. Induced movement is one of a number of phenomena—including apparent movement, autokinetic movement, and movement aftereffect—in which movement is perceived, although the corresponding distal stimulus is physically stationary. It normally results from physical movement adjoining the stationary stimulus; the induced movement is in the direction opposite that of the adjoining movement. In a typical laboratory demonstration

Abstract-When observers tracked a horizontally moving spot, the path of a second spot moving at an angle to the horizontal was radically misperceived. At a signal observers abruptly switched to tracking the second spot, which was then stabilized foveally. Data concerning resulting eye movements and perceptions support a distinction between the “central ” motor command, which is found to be formulated solely from the erroneous perception, and the motor command that finally reaches the eye. which, under some specifiable circumstances, has been “peripherally ” transformed so that the actual motion of the eye is appropriate to the actual motion of the target. INl-RODUCTION Several studies have shown that the paths of motion of spots of light moving in the dark are often strikingly