Affordance, proper function, and the physical basis of perceived heaviness

The physical basis of perceived heaviness requires consideration of the hap tic perceptual system's role in controlling actions (the system's proper fu nction) and the relation of an object's inertial properties to properties o f the human movement system (the object's affordance). We show that the mas s of a wielded object and particular scalar variables calculated from the o bject's inertia tensor combine linearly in determining perceived heaviness. The tenser-derived scalars reflect the symmetry and volume of the correspo nding inertia ellipsoid. These measures bear directly on the object's wield ability, that is, on the patterning and level of muscular forces required t o move the object in a controlled fashion. (C) 1999 Elsevier Science B.V. A ll rights reserved.