Closed-Loop Vibratory Haptic Feedback in Upper-Limb Prosthetic Users

ABSTRACT Sensory feedback, a vital element needed for interaction with the outside world, is largely unavailable for upper-limb amputees with conventional prostheses. The current study investigated four fundamental issues relating to an external vibrotactile stimulation modality for prosthetic hand force feedback: optimal tactor locations on the upper arm, feedback signal type, skin desensitization from mechanical stimulae, and effect on control of grasping force. A total of seven unilateral upper-limb amputees participated in this study. The results demonstrated optimum feedback resolution in the biceps region based on comfort and effectiveness. The average time for the skin to become desensitized to continuous stimulation was 66 seconds. Among different waveforms tested, the sinusoidal waveform was the most effective (p = 0.047). The cognitive loading test results demonstrated an improvement in grasping force due to haptic feedback at 60% of maximum grasping force (p < 0.05). Haptic feedback enhanced grasping force accuracy at specific forces rather than across all forces.