WEIGHT PERCEPTION AND THE HAPTIC SIZE WEIGHT ILLUSION ARE FUNCTIONS OF THE INERTIA TENSOR

The complex effects of mass and volume on weight perception (e.g., the size-weight illusion) were hypothesized to follow simply from invaria nts of rotational dynamics. In Experiments 1-3, the rotational inertia of wielded, occluded objects was varied independently of mass, size, and torque. Perceived heaviness depended only on rotational inertia. R eanalysis of J. C. Stevens and L. L. Rubin's (1970) study revealed tha t size's influence on weight perception depends on specific patterns o f the eigenvalues of the inertia tenser. These patterns were simulated in Experiments 4-6 with objects of fixed mass, volume, and visible si ze. Perceived heaviness decreased and increased, respectively, over ob ject sets with the eigenvalue patterns of (a) constant mass, increasin g volume and (b) increasing mass, constant volume. Weight perception a nd the size-weight illusion depend on stimulus invariants, not inferen ce.