Haptic Perceptual Instruments

University Of Connecticut, Storrs CT

Investigators

Abstract

Haptic perception refers to the perception one has of one's body, and of attachments to it, by means of the body. The term incorporates what is commonly meant by "touch," and more besides. For example, without benefit of vision, one is obviously aware of the directions of one's limbs and one can be aware of the spatial properties of objects that are wielded and hefted. These perceptual abilities are expressions of a form of haptic perception referred to as dynamic touch. It is so called because of its basis in the deformation of muscles and tendons, and the consequent activation of their receptors, by forces. The forces arise from either the muscles or the environment or both. Because of the ways in which limbs move around joints, the forces are largely rotational. This research will address the perceptual achievements of dynamic touch and their relation to the rotational dynamics of limb movements. The focus will be on the relation of these achievements to mechanical and rotational quantities, in particular the inertia tensor and attitude spinor. The tensor quantifies an object's resistance to being rotated. The spinor quantifies an object's orientation relative to some reference frame (for example, the hand) in a manner consistent with the special physical rules for combining three-dimensional rotations. A major thesis is that, in the nonvisible perception of an object's spatial dimensions by wielding or hefting, the hand-related haptic subsystem behaves as a smart instrument. It cleverly capitalizes on physical laws and on physical quantities that do not change as an object is wielded and hefted. In some of the basic methodologies, the participants will wield an unseen object to perceive its weight, length, width, or shape. Participants will respond by assigning numbers relative to a standard object or by adjusting (visible) movable surfaces or pointers to quantify the perceived properties. Often, the unseen object will be a configuration of rods that can be manipulated through the precise placement of attached metal rings to produce any desired inertia tensor. In other basic methodologies, the participants will attempt to orient a nonvisible upper limb or limb segment to another nonvisible limb. Most methodologies will involve, additionally, the acquisition of motion data on the wielded objects and limb movements and analysis by nonlinear phase-space reconstruction procedures. The major objectives will be the determination of (1) the dynamical variables governing the perception of heaviness; (2) the achievements and limits of shape perception without vision; (3) the tuning of dynamic touch, overtly and covertly, by specific experience; and (4) the basis for perceived constancy of postures. Understanding the principles governing dynamic touch should enrich our appreciation of the physical constraints that must be respected in computational and neural modeling of perceptual systems. It will provide a source of new hypotheses about somatosensory disorders and about designs for prosthetic and robot limbs. Such understanding might also be expected to motivate more intensive study of the physical principles formative of biological perception-action systems and of the cognitive and neural constraints that exploit them.