Escaping the Capacity Ceiling: Routing on the Stiefel Manifold for Bilinear SPD Layers
This work addresses challenges in cross-domain EEG decoding by proposing dynamic Stiefel routing to map input covariance matrices to subject-specific projection filters. Naive implementations fail because they collapse to ensemble averaging unless three structural fixes—a symmetric anchor, a frozen query encoder, and decoupled key alignment loss—are used. These fixes enable genuine domain-structured routing with consistent accuracy gains.