ROLE OF THE INERTIA TENSOR IN HAPTICALLY PERCEIVING WHERE AN OBJECT IS GRASPED

When an object is held and wielded, a time-invariant quantity of the w ielding dynamics is the inertia tensor I(ij). Examination of I(ij) as a function of different locations at which a cylindrical object is gra sped revealed that the off-diagonal components of I(ij)-the products o f inertia-related most systematically to grip position. In 3 experimen ts, Ss wielded an occluded rod held at an intermediate point along its length and reproduced, with the other hand, the felt grip position on a visible rod. In Experiment 1, the wielded rods were homogeneous; in Experiments 2 and 3, weights were added on either side of the grasp, with different manners of grasp contrasted in Experiment 3. In all 3 e xperiments, perceived hand position was predicted by I(ij). Discussion was focused on the role of I(ij)'s eigenvalues in perceiving the magn itudes of objects and I(ij)'s eigenvectors in perceiving hand-object r elations (e.g., position of grasp).