Efficient CSP Algorithm With Spatio-Temporal Filtering for Motor Imagery Classification

• Published in: IEEE transactions on neural systems and rehabilitation engineering Vol. 28; no. 4; pp. 1006 - 1016
• Main Authors: Jiang, Aimin, Shang, Jing, Liu, Xiaofeng, Tang, Yibin, Kwan, Hon Keung, Zhu, Yanping
• Format: Journal Article
• Language: English
• Published: United States IEEE 01.04.2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Alternative optimization scheme; Brain-computer interfaces; brain–computer interface (BCI); Channels; Classification; Classification algorithms; common spatial pattern (CSP); Computer applications; Covariance matrices; Design; EEG; Eigenvalues; Eigenvalues and eigenfunctions; electroencephalograph (EEG); Electroencephalography; Feature extraction; Filter design (mathematics); Filters; generalized eigenvalue decomposition; Image classification; Mental task performance; motor imagery; Optimization; Outliers (statistics); Regularization; reweighting technique; sparsity; Spatial filtering; spatio-temporal filters; ℓ₁ norm
• ISSN: 1534-4320; 1558-0210; 1558-0210
• DOI: 10.1109/TNSRE.2020.2979464

Common spatial pattern (CSP) is an efficient algorithm widely used in feature extraction of EEG-based motor imagery classification. Traditional CSP depends only on spatial filtering, that aims to maximize or minimize the ratio of variances of filtered EEG signals in different classes. Recent advances of CSP approaches show that temporal filtering is also preferable to extract discriminative features. In view of this perspective, a novel spatio-temporal filtering strategy is proposed in this paper. To improve computational efficiency and alleviate the overfitting issue frequently encountered in the case of small sample size, the same temporal filter is designed by EEG signals of the same class and shared by all the spatial channels. Spatial and temporal filters can be updated alternatively in practice. Furthermore, each of the resulting designs can still be cast as a CSP problem and tackled efficiently by the eigenvalue decomposition. To alleviate the adverse effects of outliers or noisy EEG channels, sparse spatial or temporal filters can also be achieved by incorporating an l 1 -norm-based regularization term in our CSP problem. The regularized spatial or temporal filter design is iteratively reformulated as a CSP problem via the reweighting technique. Two sets of motor imagery EEG data of BCI competitions are used in our experiments to verify the effectiveness of the proposed algorithm.