Cognitive feedback for use with FES upper extremity neuroprostheses

The development of two sensory substitutions systems that provide cognitive feedback for FES (functional electrical stimulation) hand-grasp-restoration neuroprostheses is described. One system uses an array of five electrodes to provide machine status information and a spatially encoded representation of the command signal that a quadriplegic individual generates to achieve proportional grasp control. Only one electrode site is active at any given instant, and a second informational channel is superimposed on the spatial position channel by modulating the frequency of the stimulus pulses. The frequency-modulated feedback channel signals six levels of force developed at the finger tips during prehension activities. The second sensory system is an integral part of an implanted FES system and utilizes a single subdermally placed electrode to display machine status information and a five-level frequency code for feedback of the user-generated grasp control signal. The multielectrode feedback system was implemented for laboratory studies using surface-mounted electrodes, although its design will ultimately incorporate subdermal electrodes to provide a highly cosmetic and unencumbering system.