Amplitude versus spatially modulated electrotactile feedback for myoelectric control of two degrees of freedom

Abstract

Objective. Artificial proprioceptive feedback from a myoelectric prosthesis is an important aspect in enhancing embodiment and user satisfaction, possibly lowering the demand for visual attention while controlling a prosthesis in everyday tasks. Contemporary myoelectric prostheses are advanced mechatronic systems with multiple degrees of freedom, and therefore, to communicate the prosthesis state, the feedback interface needs to transmit several variables simultaneously. In the present study, two different configurations for conveying proprioceptive information of wrist rotation and hand aperture through multichannel electrotactile stimulation were developed and evaluated during online myoelectric control. Approach. Myoelectric recordings were acquired from the dominant forearm and electrotactile stimulation was delivered on the nondominant forearm using a compact interface. The first feedback configuration, which was based on spatial coding, transmitted the information using a moving tactile stimulus, whereas the second, amplitude-based configuration conveyed the position via sensation intensity. Thirteen able-bodied subjects used pattern classification-based myoelectric control with both feedback configurations to accomplish a target-reaching task. Main results. High task performance (completion rate > 90%) was observed for both configurations, with no significant difference in completion rate, time to reach the target and path efficiency, respectively. Significance. Overall, the results demonstrated that both feedback configurations allowed subjects to perceive and interpret two feedback variables delivered simultaneously, despite using a compact stimulation interface. This is an encouraging result for the prospect of communicating the full state of a multifunctional hand prosthesis.

A compact system for simultaneous stimulation and recording for closed-loop myoelectric control

“…A possible reason for the change in sensation could be that different skin afferents were activated by the stimulation when rotating the wrist or that the electrode-skin adhesion was altered [66]. This could be also an additional contributing factor for higher performance in [28], where the sensation was not disturbed by muscle activation and forearm movements (due to the contralateral placement of recording and stimulation unit). Although this effect is likely to be smaller for amputees, it should be taken into consideration when future feedback schemes are designed for simultaneous EMG recording and electrotactile stimulation on the ipsilateral forearm.…”

“…5). While the control was continuous, as explained in the previous section, the feedback transmitted discrete information; the approach adopted in several other studies [27,28,[52][53][54]. Each DoF was divided into five intervals.…”

“…Although electrical stimulation can produce uncomfortable sensations if the parameters are not adjusted properly, it holds several advantages including low power consumption, independent parameter modulation and compact as well as flexible design [ 26 , 27 ]. This can be particularly advantageous when using electrode arrays to present multiple feedback variables intuitively to the user [ 28 ].…”

“…Nevertheless, the myoelectric control is also more sophisticated and relies on multichannel EMG and machine learning (classification and regression) to discriminate different movement patterns [ 34 ]. Several recent studies that employed electrotactile feedback avoided the interference by placing the recording and stimulation interface contralaterally [ 28 , 35 ] or ipsilaterally but with large spatial separation (e.g., recording from the forearm while stimulating the upper arm [ 36 ]). This allows testing in laboratory but it is not applicable clinically, where both recording and stimulation have to be fitted within a confined area of the residual limb and prosthetic socket.…”

Electrotactile Feedback for the Discrimination of Different Surface Textures Using a Microphone

“…It is commonly used to relieve pain [ 8 ] or provide electrotactile feedback [ 9 ]. In addition, TENS can play an important role in the control of manipulation tasks for prosthesis users [ 10 , 11 , 12 , 13 , 14 ] and assisting in the interpretation of objects [ 15 ]. TENS applied to the skin over the median or ulnar nerve in the amputation stump result in sensations experienced as originating from the median or ulnar nerve innervated fingers in the lost hand (somatotopic sensation) [ 16 ].…”