The (Sensorized) Hand is Quicker than the Eye: Restoring Grasping Speed and Confidence for Amputees with Tactile Reflexes

Myoelectric prosthetic hand users have difficulty with, and frequently avoid, grasping fragile objects with their prosthesis. While the sense of touch is known to be critical for human hand dexterity, it has been virtually absent in prosthetic hands. In this study, a standard myoelectric prosthetic hand was modified with tactile sensors and a simple tactile reflex to inhibit excessive forces on contact. The tactile sensors were made from an open-cell self-skinning polyurethane foam that produced a detectable increase in air pressure inside the foam when contacted. This contact signal was then used by an inhibitory reflex controller which served to reduce the gain of weaker closing signals after contact but allow stronger closing signals to pass through. Four unilateral myoelectric prosthesis users completed five trials of three different timed grasping tasks with fragile and rigid items. Subjects performed each task in three different scenarios: with their sound side limb, their current myoelectric hand, and the modified prosthesis with tactile reflex. Findings demonstrated that grasping performance with fragile objects was significantly enhanced using the modified prosthesis, even nearing the performance of subject’s sound side limb. Results suggest that this approach can substantially improve the speed and success of grasping fragile items, leading to improved use patterns, decreased cognitive effort, and improved user confidence.