Optimization of threshold for actuator control using gate-time BCI

Recently, the birthrate declines and the population ages, the number of people require nursing care and the burden on nursing care workers has been increasing. One of the attempts to support the independence and improve the quality of life of those who need care is the application of Brain-Computer Interface (BCI). BCI system was developed by us specialized for serial operation, based on EEG signals of concentration and relaxation states. In the previous study, a new system was constructed which introducing a new motor control method that introduces a new evaluation compartment concept defined as gate time in the processing of sampled EEG signals to reduce the time delay that was a problem with the conventional system. In this study, we verified the optimal threshold in the new system in order to further improve the response. Consequently, the success rate of task was as high as more than 68 % at the threshold of 40 and 50, which is an improvement of about 10 % compared to the conventional system. Furthermore, the Friedman’s test was indicating a significant difference in the success rate of task in each threshold, and the paired t-test was indicating a significant difference in the success rate of task in threshold 40 and 50. This can be concluded that the task success rate of task is significantly improved at threshold 40 and 50, and voluntary motor control is possible. The malfunction rate ranged from 21 to 31 % regardless of the threshold, and no significant difference was observed in Friedman’s test. On the other hand, the percentage of malfunction by stop increased as the threshold value increased. In addition, the subjects who successfully drove the motor at the threshold of 60 and 70 had their brains in a state of extreme concentration, and the motor continued to drive during the task section, and it took time to stop the motor even after the transition to the rest section. Since it is essential to ensure safety and to control equipment according to the user’s intentions in order to promote the use of BCI which enabled stable control of motor drive and stop, can be said to be the optimal threshold was 40 and 50.