Perceiving by Dynamic Touch the Distances Reachable With Irregular Objects

Observers wielded occluded objects and reported the distances reachable with the distal tips of the objects. Each object consisted of a cylindrical stem with two branches attached perpendicularly along its length; stem and branch lengths varied across objects. In Experiment 1, the branches were 180 deg. apart, both attached halfway along the stem. In Experiment 2, the branches were 180 deg. apart, one at one fourth and the other at three fourths of the stem length. In Experiment 3, the branches were 90 deg. apart, one at one fourth and the other at three fourths of the stem length. Observers had no foreknowledge of the objects' shapes. In each experiment, perceived reachable distance was found to be dependent on the maximum eigenvalue of the object's inertia tensor computed about the point of rotation in the wrist. Discussion focused on (a) quantifying shape for dynamic touch through the inertia ellipsoid, (b) the significance of the inertia tensor to the spatial abilities of dynamic touch, and (c) contrasting bases for theories of space perception (Lotze vs. Gibson).