Multiple Distilling-based spatial-temporal attention networks for unsupervised human action recognition

Unsupervised action recognition based on spatiotemporal fusion feature extraction has attracted much attention in recent years. However, existing methods still have several limitations: (1) The long-term dependence relationship is not effectively extracted at the time level. (2) The high-order motion relationship between non-adjacent nodes is not effectively captured at the spatial level. (3) The model complexity is too high when the cascade layer input sequence is long, or there are many key points. To solve these problems, a Multiple Distilling-based spatial-temporal attention (MD-STA) networks is proposed in this paper. This model can extract temporal and spatial features respectively and fuse them. Specifically, we first propose a Screening Self-attention (SSA) module; this module can find long-term dependencies in distant frames and high-order motion patterns between non-adjacent nodes in a single frame through a sparse metric on dot product pairs. Then, we propose the Frames and Keypoint-Distilling (FKD) module, which uses extraction operations to halve the input of the cascade layer to eliminate invalid key points and time frame features, thus reducing time and memory complexity. Finally, the Dim-reduction Fusion (DRF) module is proposed to reduce the dimension of existing features to further eliminate redundancy. Numerous experiments were conducted on three distinct datasets: NTU-60, NTU-120, and UWA3D, showing that MD-STA achieves state-of-the-art standards in skeleton-based unsupervised action recognition.