An Optimized Channel Selection Method Based on Multifrequency CSP-Rank for Motor Imagery-Based BCI System

Figure 1. Illustration of the experimental protocol for a trial in dataset 1 (a) and dataset 2 (b). (b) is replaced from Feng et al. [8] (under the creative commons attribution license/public domain).

Figure 2. Structure diagram of the CSP-R-MF algorithm.

Figure 3. Overall accuracy curves showing the accuracy behavior with the varying numbers of channel in dataset 1 (a) and dataset 2 (b). The numbers of channels is the stopping criterion of the CSP-rank algorithm. The overall accuracy curves are the average over all subjects in each dataset. The red and blue lines denote the mean validation accuracy curves of two methods, respectively.

Figure 4. ROC curves of two methods for dataset 1 and dataset 2.

Figure 5. Performance comparison of the proposed algorithm CSP-R-MF with CSP-rank in dataset 1 (a) and dataset 2 (b).

Figure 6. The topographic maps of the selected channels for two datasets under different frequency bands. Channels selected more than three times out of all subjects were marked. The channels selected by CSP-R-MF algorithm in 8–30 Hz frequency band were the same as those selected by CSP-rank algorithm. The electrode could be found in Table 2 with the number in topographic maps.