## 4 Discussion
### Implementation of BCI Application by the MSM and RP  
The results of this study suggest that the MSM is more efficient than the RP in detecting ERD. In this study, one MI was performed every 10 s, and an ERD appeared once every 10 s. However, several patients with RP required >20 s before an ERD was detected. This is presumably because ERD was detected during the second and subsequent trials and not during the first RP trial.  
Owing to the difference between the MSM and RP processing, the reaction time of the DiC suggested that the MSM required a shorter processing time than RP. This is presumably because the MSM performs computational processing while predicting the EEG change  
Figure 8: Correlation between the reaction time from event-related desynchronization (ERD) detection to DiC activation and subjective quality of motor imagery (MI) in the MSM and relative power (RP). The vertical axis shows the response time, and the horizontal axis shows the quality score regarding MI based on the visual analog scale (VAS). (**Left**) MSM, r = \(-\)0.110, \(p\) = 0.779, n = 9. (**Right**) RP, r = 0.280, \(p\) = 0.503, n = 10.  
after 1 s, and the time required for feedback is shorter than that for processing based on the RP results [21]. However, the reaction time from ERD detection to the activation of the DiC was \(>\)10 s, which is too long for real-time feedback, and the issue of shortening the robot's reaction time remains. In addition, there was no correlation between the reaction time from ERD detection to the activation of the DiC and the subjective quality of MI. Two types of MI have been reported: visual motor imagery (VMI) and kinesthetic motor imagery (KMI) [24]. A previous study showed a correlation between KMI and the ERD magnitude during MI [24]. However, the results of this study suggested that the quality of MI did not affect the time to onset of ERD. This infers that subjective KMI is not related to how quickly corticospinal excitability is transmitted but to how large the change from resting to motor imagery state is. Therefore, it is difficult to improve the quality of MI to reduce ERD detection time, and the control system needs to be adjusted by improving the application to reduce the detection time. Therefore, the DiC control system must be improved to provide real-time feedback. The current DiC is programmed to return to the initial position of elbow flexion before starting the movement to safely move the patient's joints. This movement takes approximately 5.1 s for MSM. In addition, to prepare the patient for joint movements, a countdown was provided for 4 s before the DiC performed joint movements. If the time to return to the initial position and the countdown time can be eliminated, the time can be shortened to approximately 9 s. However, at present, priority must be given to the safety of the patient's joint motions rather than eliminating the time loss of real-time feedback.  
Barrett Technologies' (Newton, MA, USA) WAM 7-degree-of-freedom arm is a BCI robot proposed by [PERSON] et al., in which each movement block is controlled [25]. WAM was set to perform one trial per block and one drive per MI, and an interval of a few seconds was provided for each block. For MI, patients are instructed to \"relax\" at the beginning, followed by MI following a \"GO\" cue. When the robot is activated, the patients are prepared for the exercise, and safety is ensured by not providing rapid assistance. The current BCI-DiC should also follow this approach and consider controlling the movement of one block and trial simultaneously.