Task-Dependent Adaptations in Closed-Loop Motor Control Based on Electrotactile Feedback

Abstract

Humans systematically adapt their strategies for closed-loop control based on visual feedback according to the dynamics of the system. Tactile feedback is a key element in many human-machine interfaces, but it is not known if and how well human control adapts to changes in system dynamics when information about the system state is provided using this type of feedback. In this study, 11 participants tracked a pseudorandom trajectory with a virtual, position-or velocity-controlled plant using a joystick. Visual or electrotactile feedback provided the instantaneous error between the target and generated trajectory. Frequency-domain system identification indicated that human control adapted in similar ways to the different control modes (i.e., position/velocity control) for both feedback modalities. For the plant dynamics modeled as gain and integrator, the human controller behaved as a low-pass filter and gain, respectively (under the assumption of quasi-linear behavior). However, while tracking quality was largely similar for both control modes with visual feedback, velocity control enabled substantially worse control with electrotactile feedback compared to position control. Furthermore, for both control modes, the crossover frequency of open-loop transfer functions was lower for electrotactile feedback (0.9 and 1.1 rad/s) than for visual feedback (1.5 and 1.7 rad/s) indicating limited control bandwidth. To summarize, closed-loop control based on electrotactile feedback enables natural adaptations in human control strategy, which is encouraging for tactile feedback-controlled human-machine interfaces, but the lower control bandwidth and lower tracking quality with velocity control may impose functional limitations.

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

“…2) Target trajectory: The target trajectory was a pseudorandom signal formed by the sum of nine sine waves with logarithmically spaced frequencies between 0.2 and 6.3 rad/s [33]. This type of reference trajectory is often used for the assessment of human manual control in tracking paradigms (e.g., see [14], [34]). The amplitudes of the five sine waves with the lowest frequencies (≤ 1 rad/s) were set to be twice as high as the amplitude of the other four sine waves to decrease the task difficulty while maintaining the desired bandwidth.…”

Biorealistic hand prosthesis with compliance control and noninvasive somatotopic sensory feedback

“…Sensory substitution via electrotactile or mechanotactile stimulation is widely studied to provide sensory information indirectly. Electrotactile substitute feedback has been applied to restore the perception of various physical features [112][113][114] or precise grasp control [115][116][117][118]. The amplitude, frequency, and pulse width of electrotactile stimulation can be modulated independently to encode a range of sensory information.…”

Peripheral Nervous System Interfaces: Invasive or Non-invasive?

“…Electro-tactile stimulation (ECS), for example, works by injecting small electrical currents across the skin, thereby not affecting muscle contractions, and maintaining compatibility with sensing techniques for intent detection (e.g., sEMG, see Došen et al, 2017). Highdensity integrated ECS delivers highly differentiated stimuli, both qualitatively and quantitatively, at essentially no additional psychological burden for the user (Dideriksen et al, 2022;Isaković et al, 2022). In my opinion, any advantage delivered by direct connection to the afferent nerves, e.g., cuff or intrafascicular electrodes [and there is ample evidence for their effectiveness, see for instance (D'Anna et al, 2019;Petrini et al, 2019)], needs to face an inevitable acceptance gap; moreover, here, too, as it was the case for ID, the technologies involved in ECS vs. invasive techniques belong to two different levels of maturity.…”