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When using EMG biofeedback to control the grasping force of a myoelectric prosthesis, subjects need to activate their muscles and maintain the myoelectric signal within an appropriate interval. However, their performance decreases for higher forces, because the myoelectric signal is more variable for stronger contractions. Therefore, the present study proposes to implement EMG biofeedback using nonlinear mapping, in which EMG intervals of increasing size are mapped to equal-sized intervals of the prosthesis velocity. To validate this approach, 20 able-bodied subjects performed force-matching tasks using Michelangelo prosthesis with and without EMG biofeedback with linear and nonlinear mapping. Additionally, four transradial amputees performed a functional task in the same feedback and mapping conditions. The success rate in producing desired force was significantly higher with feedback (65.4±15.9%) compared to no feedback (46.2±14.9%) as well as when using nonlinear (62.4±16.8%) versus linear mapping (49.2±17.2%). Overall, in able-bodied subjects, the highest success rate was obtained when EMG biofeedback was combined with nonlinear mapping (72%), and the opposite for linear mapping with no feedback (39.6%). The same trend was registered also in four amputee subjects. Therefore, EMG biofeedback improved prosthesis force control, especially when combined with nonlinear mapping, which showed to be an effective approach to counteract increasing variability of myoelectric signal for stronger contractions.

Enhancing the perception of the surrounding environment by conveying information through tactile stimulation can improve performance, especially when other senses are already overloaded (e.g., first responders). Delivering electrotactile messages using spatiotemporal patterns has been suggested as an efficient and reliable approach to transmitting information through the skin. However, the effectiveness of this approach depends on the user’s capability to recognize tactile messages in potentially challenging scenarios (e.g., rescue operations). Therefore, the present study evaluated the participants’ performance in identifying electrotactile messages while they performed a parallel cognitive task. Thirty-six electrotactile messages were delivered through a 3 × 2 pad-matrix at the lateral torso in the baseline and multitasking conditions. The task-switching paradigm was employed as the parallel task, introducing cognitive interference to the electrotactile message recognition. The assumption was that the simultaneous task would impair the identification performance, but that this impairment could be minimized by decreasing the speed at which the message was delivered. The results indeed showed that the identification success rates decreased from ~83% in the baseline to ~61% during multitasking. Unexpectedly, the performance did not recover when the message duration was increased. Hence, modulating the message duration seems not to be an effective strategy to prevent lower performance while multitasking.

The present work introduces preliminary re-sults of an EU H2020 project aiming to develop an un-obtrusive system to assist first responders by conveying additional information through electrotactile feedback. This study assessed three different encoding schemes for delivering tactile messages in form of spatial patterns. Patterns were delivered using simultaneous activation, sequential activation, and sequential activation with fre-quency modulation of pads. Biphasic pulses with a pulse duration of 400 μs and frequency of 25, 50 and 150 Hz were delivered through a surface electrode (2 × 3 matrix array) placed at the lateral torso. The success rate in iden-tification of electrotactile spatial patterns was quantified in healthy subjects. Simultaneous activation resulted in poor performance, improving with the sequential ap-proach. The best results were achieved using mixed en-coding (sequential activation plus frequency modulation) with success rates of approximately 80%. These prelimi-nary results suggest the feasibility of conveying and iden-tifying electrotactile spatial patterns at the lateral torso when the encoding scheme incorporates spatiotemporal stimulation profiles, rather than simultaneous electrode activation. These are encouraging results since reliable recognition of spatial patterns can enable high- bandwidth communication through tactile channels.