Evolution of users' subjective experience over three training sessions with an EEG Motor-Imagery Brain-Computer Interface (MI-BCI).

Motor Imagery-based Brain-Computer Interfaces (MI-BCIs) have been shown to be promising for numerous applications, including sport training and entertainment for healthy users, but also for improving or restoring functions in neurological and neuropsychiatric disorders, e.g., for motor rehabilitation post-stroke or for attention training in attention deficits. Reliable interactions with such MI-BCIs require a heavy training process for both the machine and the user. Yet, how User eXperience (UX) evolves during standard training is still largely unclear, both within and between sessions/days. Through an exploratory study, we investigated the variations of users' answers to a UX questionnaire when training with a standard left vs. right-hand MI-BCI. 24 healthy novice users engaged in 3 training sessions (with 12 runs each) on different days. Each short run was followed by six questions on screen measuring UX factors on scales from 1 to 10: mental demand, performance, mental effort, frustration, mental fatigue and anxiety. Interestingly, BCI performances did not correlate with any subjective UX measure in this study. However, a time effect was observed. Within session, the results suggested that mental demand, effort, and fatigue significantly augmented during BCI operation, and that frustration significantly fluctuated but did not differ pre- vs. post-session. Between sessions, the first session was rated significantly more challenging than the other two regarding frustration, anxiety, mental demand, mental effort and mental fatigue. This highlights the importance of conducting studies across sessions and of considering the users' mental states during BCI use, for improving UX and thus possibly BCI treatment outcome.