Co-location of force and action improves identification of force-displacement features

Haptic display is a promising means to deliver sensory feedback to an amputee from an upper limb prosthesis equipped with electronic sensors. Haptics, however, describes a diverse set of sensory and perceptual modalities. The question arises: which modality might best serve the purposes of the prosthesis wearer, and which body site should be used? To begin to answer these questions, we have conducted an experiment involving n=14 participants in which reaction force was displayed either to the same hand used to explore a virtual object (co-located condition), or to the opposing hand (non co-located condition). In randomly ordered trials, reaction forces were derived from the commanded motion according to one of three force-displacement relationships, describing a linear spring, a softening spring, and a stiffening spring. All springs shared a common rest length and terminal force. Results indicate a significant difference between the co-located and non co-located force display conditions in terms of identification accuracy and time length. Our findings suggest that those haptic modalities that are capable of coupling action and re-action will provide the most utility to amputees with an upper limb prosthesis.