Toward Subject Invariant and Class Disentangled Representation in BCI via Cross-Domain Mutual Information Estimator

In recent, deep learning-based feature representation methods have shown a promising impact in electroencephalography (EEG)-based brain-computer interface (BCI). Nonetheless, due to high intra- and inter-subject variabilities, many studies on decoding EEG were designed in a subject-specific manner by using calibration samples, with no much concern on its less practical, time-consuming, and data-hungry process. To tackle this problem, recent studies took advantage of transfer learning, especially using domain adaptation techniques. However, there still remain two challenging limitations; i) most domain adaptation methods are designed for labeled source and unlabeled target domain whereas BCI tasks generally have multiple annotated domains. ii) most of the methods do not consider negatively transferable to disrupt generalization ability. In this paper, we propose a novel network architecture to tackle those limitations by estimating mutual information in high-level representation and low-level representation, separately. Specifically, our proposed method extracts domain-invariant and class-relevant features, thereby enhancing generalizability in classification across. It is also noteworthy that our method can be applicable to a new subject with a small amount of data via a fine-tuning, step only, reducing calibration time for practical uses. We validated our proposed method on a big motor imagery EEG dataset by showing promising results, compared to competing methods considered in our experiments.