Multichannel Electrotactile Feedback With Spatial and Mixed Coding for Closed-Loop Control of Grasping Force in Hand Prostheses

Abstract

Abstract-Providing somatosensory feedback to the user of a myoelectric prosthesis is an important goal since it can improve the utility as well as facilitate the embodiment of the assistive system. Most often, the grasping force was selected as the feedback variable and communicated through one or more individual single channel stimulation units (e.g., electrodes, vibration motors). In the present study, an integrated, compact, multichannel solution comprising an array electrode and a programmable stimulator was presented. Two coding schemes (15 levels), spatial and mixed (spatial and frequency) modulation, were tested in able-bodied subjects, psychometrically and in force control with routine grasping and force tracking using real and simulated prosthesis. The results demonstrated that mixed and spatial coding, although substantially different in psychometric tests, resulted in a similar performance during both force control tasks. Furthermore, the ideal, visual feedback was not better than the tactile feedback in routine grasping. To explain the observed results, a conceptual model was proposed emphasizing that the performance depends on multiple factors, including feedback uncertainty, nature of the task and the reliability of the feedforward control. The study outcomes, specific conclusions and the general model, are relevant for the design of closed-loop myoelectric prostheses utilizing tactile feedback.

Touch on predefined areas on the forearm can be associated with specific fingers: Towards a new principle for sensory feedback in hand prostheses

“…It has been shown that sensory feedback improves grasping control and performance with myoelectric hand prostheses in inexperienced users (10,11). Both invasive and non-invasive sensory feedback systems are under development (2,9,(12)(13)(14)(15)(16)(17)(18)(19).…”

Electrotactile feedback improves performance and facilitates learning in the routine grasping task

“…Therefore, the provision of feedback improved the quality of force control in both accuracy (MAE) and precision (STDAE). Importantly, contrary to previous studies, 10,13 the present experiment included a realistic task, in which the subjects needed to generate four levels of force in a random order (as when grasping a sequence of objects in real life). At the same time, the feedback was transmitted using a practically relevant method, i.e., a multichannel electrotactile interface implementing a low-resolution feedback (6 discrete levels).…”

Integrated and flexible multichannel interface for electrotactile stimulation

“…Since the two coding schemes are perceptually separated (spatial localization versus frequency perception), it is likely that the SR for the mixed coding including combined spatial and frequency modulation would not be substantially different from that obtained for the single coding, i.e., spatial only or frequency only. We base this assumption on the results from our recent study [55], where mixed spatial (5 levels) and frequency (3 levels) coding was tested and the overall SR for the 15 codes (5×3) was 87%, with the marginal SR of 93% and 95% for the spatial and frequency levels. This was similar SR to that obtained for 6 spatial and 3 frequency levels in the present study (88% and 99%, respectively).…”