Online Closed-Loop Control Using Tactile Feedback Delivered Through Surface and Subdermal Electrotactile Stimulation

Abstract

AimLimb loss is a dramatic event with a devastating impact on a person’s quality of life. Prostheses have been used to restore lost motor abilities and cosmetic appearance. Closing the loop between the prosthesis and the amputee by providing somatosensory feedback to the user might improve the performance, confidence of the amputee, and embodiment of the prosthesis. Recently, a minimally invasive method, in which the electrodes are placed subdermally, was presented and psychometrically evaluated. The present study aimed to assess the quality of online control with subdermal stimulation and compare it to that achieved using surface stimulation (common benchmark) as well as to investigate the impact of training on the two modalities.MethodsTen able-bodied subjects performed a PC-based compensatory tracking task. The subjects employed a joystick to track a predefined pseudorandom trajectory using feedback on the momentary tracking error, which was conveyed via surface and subdermal electrotactile stimulation. The tracking performance was evaluated using the correlation coefficient (CORR), root mean square error (RMSE), and time delay between reference and generated trajectories.ResultsBoth stimulation modalities resulted in good closed-loop control, and surface stimulation outperformed the subdermal approach. There was significant difference in CORR (86 vs 77%) and RMSE (0.23 vs 0.31) between surface and subdermal stimulation (all p < 0.05). The RMSE of the subdermal stimulation decreased significantly in the first few trials.ConclusionSubdermal stimulation is a viable method to provide tactile feedback. The quality of online control is, however, somewhat worse compared to that achieved using surface stimulation. Nevertheless, due to minimal invasiveness, compactness, and power efficiency, the subdermal interface could be an attractive solution for the functional application in sensate prostheses.

Closed-loop Manual Control with Tactile or Visual Feedback under Wireless Link Impairments

“…The target trajectory is normally a pseudorandom signal to prevent the HO from learning the pattern and using feed-forward control. Several studies already used (compensatory) tracking tasks to investigate local, direct control [12]- [17], establishing the detrimental effects of latency on performance [18]- [21].…”

“…Electrotactile [14] and vibrotactile [15] stimulation have been studied in target tracking tasks, where pulse width and frequency modulation were used to convey the error magnitude to the subjects. The effect of stimulation frequency on the subject's ability to understand and exploit the feedback information [16] and the difference between the surface and subdermal stimulation [17] approaches have also been considered. All these studies were conducted in laboratory settings assuming an ideal transmission of feedback and commands.…”