An Information Space for Partial Length Perception in Dynamic Touch

Abstract

In 2 experiments, participants held a rod, which was occluded from view, at some position along its length and reported the 2 partial lengths—the lengths to the left and to the right of the hand. In Experiment 1, the possible importance of gravitational torque was investigated by comparing judgments made during freely wielding a rod with judgments made during wielding it about a fixed horizontal axis. Performance was better in the free condition, but participants' moderate success in the fixed condition implicated the importance of gravitational torque. In Experiment 2, in which the fixed axis was vertical so no gravitational torque was available, participants could not discriminate longer and shorter sides, though the sum (total rod length) correlated highly with the sum of the 2 partial-length judgments, implicating the importance of inertial moment alone. The results imply that a variable space that captures partial lengths can be derived from moment of inertia and gravitational torque, at least when rods are rotated on a fixed access, and thus when no off-diagonal terms from the inertia tensor are in play.