Measures of fatigue and performance are related to user interface and task in a communication BCI

Objective. This exploratory study compared two non-implantable communication brain-computer interfaces (cBCIs) to determine whether physiologic and self-report measures of mental fatigue, effort, and boredom were greater during calibration than during copy-spelling and whether there were differences between two common cBCI interfaces, rapid serial visual presentation (RSVP) and single-character presentation matrix (SCP-matrix).Approach. Twenty-three healthy adults successfully utilized both RSVP and SCP-matrix speller cBCIs in a single experimental session. Participants completed a calibration task and three online (closed-loop) copy-spelling tasks for each interface and provided self-report data on state mental fatigue, effort, and boredom. Physiological measures included EEG recordings alongside autonomic markers, including blood pressure, heart rate, respiration rate, and pulse rate variability.Main results. Participants reported significant increases in perceived mental fatigue, effort, boredom, and sleepiness during the session, with significant increases during calibration compared to copy-spelling. On average, users typed 1.5 more correct characters per copy-spelling phase using the SCP-matrix interface than when using RSVP. Results for autonomic and self-report metrics were consistent with fatigue being increased during calibration tasks relative to copy-spelling. EEG measures showed increased absolute and relative alpha activity and decreased relative theta activity during calibrations compared to copy-spelling, and increased absolute and relative alpha activity and decreased relative theta activity during RSVP, compared to matrix. P300 amplitude on average was greater during copy spelling tasks than during calibrations.Significance. Participants demonstrated increased fatigue while using non-implantable cBCIs. Evidence suggested that calibration tasks for both interfaces were more fatiguing, required more mental effort, and were less engaging than copy-spelling tasks. Increased user fatigue and perceived mental effort remain significant barriers to sustained use of non-implantable cBCI systems. Though limited, the current study enhances our understanding of user experience with cBCIs and emphasizes the need to design more engaging and concise calibration procedures.