Comparison of linear frequency and amplitude modulation for intraneural sensory feedback in bidirectional hand prostheses

Abstract

Recent studies have shown that direct nerve stimulation can be used to provide sensory feedback to hand amputees. The intensity of the elicited sensations can be modulated using the amplitude or frequency of the injected stimuli. However, a comprehensive comparison of the effects of these two encoding strategies on the amputees’ ability to control a prosthesis has not been performed. In this paper, we assessed the performance of two trans-radial amputees controlling a myoelectric hand prosthesis while receiving grip force sensory feedback encoded using either linear modulation of amplitude (LAM) or linear modulation of frequency (LFM) of direct nerve stimulation (namely, bidirectional prostheses). Both subjects achieved similar and significantly above-chance performance when they were asked to exploit LAM or LFM in different tasks. The feedbacks allowed them to discriminate, during manipulation through the robotic hand, objects of different compliances and shapes or different placements on the prosthesis. Similar high performances were obtained when they were asked to apply different levels of force in a random order on a dynamometer using LAM or LFM. In contrast, only the LAM strategy allowed the subjects to continuously modulate the grip pressure on the dynamometer. Furthermore, when long-lasting trains of stimulation were delivered, LFM strategy generated a very fast adaptation phenomenon in the subjects, which caused them to stop perceiving the restored sensations. Both encoding approaches were perceived as very different from the touch feelings of the healthy limb (natural). These results suggest that the choice of specific sensory feedback encodings can have an effect on user performance while grasping. In addition, our results invite the development of new approaches to provide more natural sensory feelings to the users, which could be addressed by a more biomimetic strategy in the future.

Psychometric characterization of incidental feedback sources during grasping with a hand prosthesis

“…Some studies showed significant improvements in performance with artificial somatosensory feedback [35][36][37]. However, these studies were conducted while controlling a virtual setup [35][36][37] and/or while blocking the incidental (visual and auditory) feedback sources [18,31,36,38]. Some recent studies showed benefits of feedback in realistic, clinical settings [32,[39][40][41][42][43].…”

On the Reliability of Chronically Implanted Thin-Film Electrodes in Human Arm Nerves for Neuroprosthetic Applications

“…Use of iridium oxide as stimulation contact material with its high charge injection capacities kept the stimulation sites well in the chemically safe charge injection regime. Further analysis, development and improvement of the TIMEs in terms of material integrity by using adhesion promoters between thin-film metallization and the polymeric substrate [39], enabled chronic application in three upper limb amputees [10][11][12]16,[40][41][42]. Within this study, we present the analysis of implants used in the mentioned clinical studies implanted for up to six months.…”

Temporal Modulation of the Response of Sensory Fibers to Paired-Pulse Stimulation

“…A number of devices that interface directly with the peripheral nerves have been developed to provide electrode stimulation [3], [11]. These neural interfaces include intrafascicular electrodes that penetrate the nerves (TIMEs [6], [12], [13], LIFEs [14], [15]) and cuff electrode arrays that wrap around the nerve without penetrating it (Spiral cuffs [1], [16], FINEs [17], [18]). Generally, nerve cuff electrode arrays do not stimulate as selectively as intrafasciular electrode arrays.…”

“…Testing of multi-channel cuffs in humans has mainly focused on the ability to modulate the perceived sensation by tuning the frequency, amplitude, or pulse width delivered by a single electrode [1], [2], [4], [6]. Spatio-temporal patterns of electrical stimulation delivered from multiple electrodes has the potential to provide patients with different sensations experienced concurrently.…”