Grasping in wonderland: altering the visual size of the body recalibrates the body schema

Can viewing our own body modified in size reshape the bodily representation employed for interacting with the environment? This question was addressed here by exposing participants to either an enlarged, a shrunken, or an unmodified view of their own hand in a reach-to-grasp task toward a target of fixed dimensions. When presented with a visually larger hand, participants modified the kinematics of their grasping movement by reducing maximum grip aperture. This adjustment was carried over even when the hand was rendered invisible in subsequent trials, suggesting a stable modification of the bodily representation employed for the action. The effect was specific for the size of the grip aperture, leaving the other features of the reach-to-grasp movement unaffected. Reducing the visual size of the hand did not induce the opposite effect, although individual differences were found, which possibly depended on the degree of subject's reliance on visual input. A control experiment suggested that the effect exerted by the vision of the enlarged hand could not be merely explained by simple global visual rescaling. Overall, our results suggest that visual information pertaining to the size of the body is accessed by the body schema and is prioritized over the proprioceptive input for motor control.