Sufficiency of Longitudinal Moment of Inertia for Haptic Cylinder Length Judgments

Many studies invoke moment of inertia (I) as necessary and sufficient information to perceive cylinder length via wielding, yet some assert that l(ii) is neither necessary (weight, or, or static moment, M. are sufficient) nor sufficient for length judgments (or or M is necessary). Mathematical expressions for l(ii) not involving or or M imply length, so l(ii) could be sufficient for cylinder length judgments. In 5 experiments (N = 113), only longitudinal l(ii) (the smallest principal value) informed cylinder length estimates in a novel task, rolling. Experiment 1 yielded reliable length judgments. Varying diameter supported length scaling (Experiment 2); similar length estimates occurred with both rolling and wielding (Experiment 3); feedback improved rolling length judgments to levels commensurate with wielding (Experiment 4); and length judgments shifted predictably with added mass (Experiment 5). Contrary to proposals in the literature, l(ii) is sufficient information for cylinder length judgments, absent m or M information, even when l(ii) is of minimal magnitude and the task quite novel.