Planning to reach for an object changes how the reacher perceives it.

Three experiments assessed the influence of the Ebbinghaus illusion on size judgments that preceded verbal, grasp, or touch responses. Prior studies have found reduced effects of the illusion for the grip-scaling component of grasping, and these findings are commonly interpreted as evidence that different visual systems are employed for perceptual judgment and visually guided action. In the current experiments, the magnitude of the illusion was reduced by comparable amounts for grasping and for judgments that preceded grasping (Experiment 1). A similar effect was obtained prior to reaching to touch the targets (Experiment 2). The effect on verbal responses was apparent even when participants were simply instructed that a target touch task would follow the verbal task. After participants had completed a grasping task, the reduction in the magnitude of the illusion remained for a subsequent verbal-response judgment task (Experiment 3). Overall, the studies demonstrate strong connections between action planning and perception.