Changes in the planning and control of discrete aiming movements in response to the introduction and removal of the Ebbinghaus size-contrast illusion were examined. Movements were executed faster to targets that appeared larger following movement initiation. The differences in movement time were associated with the portion of the movement associated with on-line control. The results are inconsistent with the assumptions of the planning and control model [Behav. Brain Sci. (in press); J. Exp. Psychol. Hum. Perc. Perf. 27 (2001) 560], and the perception and action dissociation model of goal-directed movement [A.D. Milner, M.A. Goodale, The Visual Brain in Action, Oxford University Press, New York, Oxford, 1995].