Sense of Agency in Closed-loop Muscle Stimulation

To maintain a user's sense of agency (SoA) when working with a physical motor augmentation device, the actuation must align with the user's intentions. In experiments, this is often achieved using stimulus-response paradigms where the motor augmentation can be optimally timed. However, in the everyday world users primarily act at their own volition. We designed a closed-loop system for motor augmentation using an EEG-based brain-computer interface (BCI) to cue users' volitional finger tapping. Relying on the readiness potentials, the system autonomously cued the finger movement at the time of the intent to interact via electrical muscle stimulation (EMS). The prototype discriminated pre-movement from idle EEG segments with an average F1 score of 0.7. However, we found only weak evidence for a maintained SoA. Still, participants reported a higher level of control when working with the system instead of being passively moved.