Learning Representations by Contrastive Spatio-Temporal Clustering for Skeleton-Based Action Recognition
Why this work is in the frame
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Bibliographic record
Abstract
Self-supervised representation learning has proven constructive for skeleton-based action recognition. For better performance, existing methods mainly focus on 1) multi-modal data augmentations and 2) triplet contrastive samples construction. However, designing these strategies is always heuristics and hard. Instead of exploring more similar strategies, this paper addresses this issue with a different view and proposes a novel Contrastive Spatio-Temporal Clustering (CSTC) module. CSTC constructs a supervised signal (pseudo-label) of action sequences in an online clustering manner, and it is complementary to the recent data augmentations or triplet contrastive samples construction strategies. Specifically, CSTC can be formulated as an optimal transport problem. we introduce the spatio-temporal regularizations into the original optimal transport term to guide the pseudo-label generation, i.e., a semantic regularization learned by frame index is proposed to constrain the frame order, and a prior normal distribution regularization based on sampling characteristics of samples is proposed to maintain the dependability of spatial cluster assignments. Furthermore, to enhance the learning of latent features, we propose a Bidirectional Cross-modal Clustering Consistency Objective (B3CO) to enforce cluster assignments consistency for different modalities of the same sample. Last, since fusing spatial and temporal clustering losses directly during back-propagation will confuse the learned dimension-specific semantics, we propose a simple yet effective training strategy to fix it by training the model using these two losses alternately. By integrating the above designs into the MoCo framework, we propose a Contrastive Spatio-Temporal Clustering Network (CSTCN), which can excavate cross-modal discriminative spatio-temporal features in the clustering space. Experimental results on NTU RGB+D 60, NTU RGB+D 120, and PKU-MMD II datasets show that CSTCN achieves state-of-the-art performance in both single- and multi-modal models, especially in the KNN and semi-supervised evaluation protocols. Besides, the key module CSTC shows good generalization capability, and achieves consistent performance improvement on the basis of several state-of-the-art methods which focus on data augmentations and triplet contrastive samples construction.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it