Generalization Beyond Feature Alignment: Concept Activation-Guided Contrastive Learning

Learning invariant representations via contrastive learning has seen state-of-the-art performance in domain generalization (DG). Despite such success, in this paper, we find that its core learning strategy -- feature alignment -- could heavily hinder the model generalization. Inspired by the recent progress in neuron interpretability, we characterize this problem from a neuron activation view. Specifically, by treating feature elements as neuron activation states, we show that conventional alignment methods tend to deteriorate the diversity of learned invariant features, as they indiscriminately minimize all neuron activation differences. This instead ignores rich relations among neurons -- many of them often identify the same visual concepts though they emerge differently. With this finding, we present a simple yet effective approach, \textit{Concept Contrast} (CoCo), which relaxes element-wise feature alignments by contrasting high-level concepts encoded in neurons. This approach is highly flexible and can be integrated into any contrastive method in DG. Through extensive experiments, we further demonstrate that our CoCo promotes the diversity of feature representations, and consistently improves model generalization capability over the DomainBed benchmark.