The Role of Rotational Inertia in the Haptic and Haptic + Visual Size-Weight Illusions

In 2 experiments, the role of rotational inertia in perceiving heaviness was investigated. Rotational inertia has been shown previously to be responsible for one's perception of heaviness and the size-weight illusion when the perceiver is using dynamic touch. In both of the experiments reported here, participants rated the heaviness and volume of a set of stimuli that varied in both mass and volume. In Experiment 1, participants were able to grasp but not view the stimuli (haptic touch). In Experiment 2, participants were able to both grasp and view the stimuli (haptic touch + vision). Because the stimuli were lifted by the participants in each experiment, dynamic touch was available. In each case, reports of perceived heaviness were a function of rotational inertia. As additional information became available through haptic touch or vision, however, perceivers became more sensitive to the variations in rotational inertia. These results suggest that perceivers use rotational inertia to perceive heaviness in a variety of situations and that multiple modalities may be used to detect the same information.