Data and analyses

When grasping an object, grip aperture and grip force are scaled to the visually predicted size and mass of the object even before touching and lifting it. Size-weight expectations are not only involved in action tasks but also play a central role in perceptual judgments, which when not met can lead to illusions such as the size-weight illusion. We here find that early visual deprivation, even if followed by years of visual experience and interaction with real world objects, highly impairs the natural control of grasping although the size-weight illusion does develop rapidly after sight restoration.