Participants had a chance to respond with three comments to each open-ended question. Their responses were sorted in five categories, as shown in Figure 12(a). Except for one subject who did not comment on or identify any problem, others gave a total of 24 responses to the first question. Seven issues were related to the headgear (4 about its appearance and 3 about its mechanical stability). Seven responses were about the system accessibility, including the speed of cursor movement, PWC speed, system calibration, and training. Three were related to the tongue piercing, and three were about the system being limited to interfacing only with certain applications. Finally, there were three responses about technical issues that had happened during the trial.