Perception-Action Dissociation Generalizes to the Size-Inertia Illusion Running title: Perception-Action Dissociation in Size-Mass Illusions

Two objects of similar visual aspects and of equal mass, but of different sizes, generally do not elicit the same percept of heaviness in humans. The larger object is consistently felt to be lighter than the smaller, an effect known as the ‘size-weight illusion’. We investigated whether the same effect can be observed if the mass of an object is available to participants through inertial rather than gravitational cues. We compared the responses of ten participants in two experimental conditions, where they manipulated objects supported by a frictionless, air bearing slide that could be oriented vertically or horizontally. We also analyzed the participants ’ anticipatory motor behavior by measuring the grip force prior to motion onset. We found that the perceptual illusory effect was qualitatively the same in the two conditions and observed that both visual size and haptic mass had a negligible effect on the anticipatory gripping control of the participants in the gravitational and inertial conditions, despite the enormous differences in the mechanics of the two conditions. Key words: mass perception; motor programming; precision grip; sensorimotor integration; huma