ST-GF: Graph-based Fusion of Spatial and Temporal Features for EEG Motor Imagery Decoding

The Motor Imagery (MI) decoding based on electroencephalogram (EEG), has promising applications. However, most current methods face two main issues: (1) They usually rely on convolutional neural networks to extract temporal features of MI signals without fully considering the brain's functional connectivity during MI tasks. (2) They lack analysis and recognition of MI features slices and non-tasks slices within EEG signals, leading to poor generalization and robustness. To address these problems, we propose a novel deep learning model based on graph neural network to learn spatial features between multiple electrode channels and integrate the brain's functional connectivity features. Additionally, it restructures time slices features segmented by the sliding time window algorithm to enhance MI temporal features in EEG signal. Therefor our model achieves the fusion of spatial and temporal features. To enhance the convergence effect of the model, we introduce electrode channel spatial positions as prior knowledge to initialize the parameters of the graph convolutional network parameters. Experimental evaluations on the publicly available EEG MI dataset from BCI Competition IV 2a show that our model achieves a four-class cross-session classification accuracy of 82.38%. Compared with other methods, our model yields the best results, demonstrating its superiority. Furthermore, the results indicate that the spatial feature obtained through our model bears resemblance to the brain functional connectivity patterns identified during MI tasks. To conclude, the fusion of spatial and temporal features with graph model shows the great application potential for EEG MI signals decoding and other EEG analysis.