Haptic perception of partial-rod lengths with the rod held stationary or wielded

Three experiments on the haptic perception of partial-rod lengths are reported. The rods were gripped between the two ends and held horizontal. The subjects held the rods stationary; the distribution of mass of the segment in front of the hand was fixed, while the distribution of mass of the segment behind the hand was varied. Perceived forward length was found to be significantly affected by the distribution of mass of the backward segment. Similar results were obtained when the rods were wielded. The results indicated that partial-rod lengths are specified by functions of mechanical perturbations acting on the hand, and not by the breaking up of the first moment of mass or the moment of inertia of the rod by attention as suggested previously by others. The results are also discussed with respect to invariant detection and attention.