Rectifying Geometric Misalignment: Online Source-Free Adaptation for Class-Imbalanced EEG
This work addresses the degradation of Riemannian manifold geometric alignment in online brain–computer interfaces caused by label shift. To tackle this issue without access to source-domain data, the authors propose the Online Streaming Plug-and-Play Domain-Invariant Manifold (OSPDIM) framework, which introduces manifold-constrained bias into tangent space mapping for the first time. By integrating an online information maximization criterion, OSPDIM adaptively optimizes bias parameters in real time, enabling plug-and-play geometric correction without reliance on historical batch statistics. Experimental results demonstrate that OSPDIM significantly outperforms standard Riemannian methods across multiple motor imagery EEG datasets, exhibiting exceptional robustness—particularly under severe class imbalance in online settings.