Towards optimizing the non-invasive sensory feedback interfaces in a neural prosthetic control

Abstract

Objective. The somatotopic interface (SI) and non-somatotopic interface (NI) are commonly used to provide non-invasive sensory feedback. Nevertheless, differences between SI and NI are rarely reported, and objective evaluations of the corresponding brain response are missing as well. Few studies have reported how to design the stimulation encoding based on the two interfaces. The objective of this study was to investigate the difference in sensory characteristics between SI and NI, and propose an optimal encoding method for non-invasive feedback interfaces. Approach. We recruited seven amputees and compared the tactile sensitivity to stimulated positions and intensities between SI (phantom finger area) and NI (upper arm) in a tactile discrimination task. Electroencephalography (EEG) evaluation task was subsequently conducted to objectively evaluate the stimulus-evoked brain response. Finally, the two kinds of tactile information (stimulated position and intensity) was applied to an object recognition task. Specifically, the object size was reflected by the prosthetic finger position through stimulated position encoding, and the object stiffness was reflected by the contact force of prosthetic fingers through stimulated intensity encoding. We compared the performance under four feedback conditions (combinations between two kinds of tactile information and two interfaces). Results. Behavioral results showed that NI was more sensitive to position information while SI was more sensitive to intensity information. EEG results were consistent with behavioral results, showing a higher sensitivity of sensory alpha ERD for NI in the position discrimination, while the trend was opposite in the intensity discrimination. The feedback encoding allowed amputees to discriminate the size and stiffness of nine objects with the best performance of 62% overall accuracy (84% for size discrimination, 71% for stiffness discrimination) when position and intensity information was delivered on the NI and SI, respectively. Signicance. Our results provided an instructive strategy for sensory feedback via non-invasive solutions.

Neural evidence for functional roles of tactile and visual feedback in the application of myoelectric prosthesis

“…Choosing the fingertip as the feedback area could maximally approximate the evoked sensations of the amputees in sensory feedback. In our previous work, we have also proved that the sensory mechanisms of the phantom finger area were similar to normal fingers in terms of EEG response to the electrotactile stimulation [51]. From this perspective, choosing the fingertip as the feedback area could also provide a reference for investigating the brain response of amputees in the closedloop prosthesis control task.…”

Study of Tactile Sensation Somatotopy and Homology Between Projected Fingers in Residual Limb and Natural Fingers in Intact Limb

“…2, a Matlab-installed computer is used to control and program the Master-9 stimulator. According to previous research [21], [22], [27], [29], multi-pulse of biphasic, rectangular, and charged-balanced current pulses are produced to evoke tactile sensation (see Fig. 3(a)).…”

“…In the preliminary experiment, the SSSEP paradigm (steadystate somatosensory evoked potential) is considered as a suitable paradigm to evoke a strong somatosensory sensation [22]. Since the PFM configuration had been obtained in the screening procedure, the preliminary experiment is necessary to further determine the stimulation parameters.…”

“…Since the PFM configuration had been obtained in the screening procedure, the preliminary experiment is necessary to further determine the stimulation parameters. In early studies [21], [22], [32], it is suggested that the stimulation frequency ranged from 20 to 50 Hz, where high frequent stimulation (50 Hz) evokes buzzing and low frequent stimulation (20 Hz) evokes vibration. Since the buzz sensation has the advantage of owning a wide modulation range [21], this advantage can be used to find the boundary for the wide range of tactile sensations.…”

“…Compared to the invasive interface, the non-invasive interface is much more acceptable for amputees [3]. Second, considering the type of restoration, the artificial interface could have two types, sensory rebuild [15]- [18], [21] and sensory substitution [22], [23]. Compared to the sensory substitution that is building a new sensory stream to the brain and needs the users to learn via days of training [26], the sensory rebuild is trying to connect the tactile stimulation via the residual nerve pathway, where thus sensory rebuild is a natural way to be able to deliver more kinds of tactile sensations intuitively without learning [3], [27].…”