Input-output nonlinearities and time delays increase tracking errors in hand grasp neuroprostheses

Grasp force tracking tasks were designed to study how different input-output relationships (nonlinearities and time delays) would affect the performance of the functional neuromuscular stimulation (FNS) hand grasp neuroprosthesis. Simulated hand grasp neuroprostheses and real hand grasp neuroprostheses with and without closed loop control were evaluated, with the subjects adjusting the input to the system so that the output would match a visual target track at three different bandwidths (normals with the simulated systems; neuroprosthesis users with the real systems). For both systems, the tracking error increased as the input-output nonlinearity increased. Other factors that were seen to affect tracking performance were the target bandwidth and delays in the neuroprosthesis