Progressive semantic learning for unsupervised skeleton-based action recognition

Traditional contrastive learning frameworks for skeleton-based action recognition use data augmentation and memory bank techniques to obtain positive/negative samples required for training, but this instance-level pseudo-label generation mechanism does not take full advantage of the rich cluster-level semantic information contained in human skeleton sequences. In this paper, we propose a Progressive Semantic Learning method (ProSL), which gradually optimizes the pseudo-label generation mechanism in self-supervised contrastive learning through an iterative framework, so that representation learning can effectively capture action semantic information. Specifically, the existing contrastive learning methods can output an initial skeleton encoder. Then, on the basis of this encoder, clustering methods can be applied to generate a Codebook containing the semantic information of human actions, which is further used to improve the pseudo-label generation mechanism. Finally, based on the above two-step iterations, we achieve progressive semantic learning and obtain a more reasonable skeleton encoder. Extensive experiments on four datasets demonstrate that our proposed method achieves SOTA on multiple downstream tasks.