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OLMD: Orientation-aware Long-term Motion Decoupling for Continuous Sign Language Recognition
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Proposes OLMD, a single-cue CSLR framework that aggregates long-term motion (LMA), decouples features into horizontal and vertical components for orientation-aware purification, and couples them within and across stages, reaching SOTA WER on PHOENIX14, PHOENIX14-T and CSL-Daily.
Problem
Continuous sign language recognition struggles with multi-orientational and long-term motions, which current RGB-based CSLR models capture poorly (they analyze only 1-2 adjacent frames and treat all orientations as one).
Approach
A Long-term Motion Aggregation module built on sliding-window feature differences suppresses static background, then motion features are pooled into horizontal and vertical components that are purified by separate 2D-CNN blocks, and coupled back within and across stages.
Key results
- OLMD reaches 17.1% Dev and 17.2% Test WER on PHOENIX14, improving over the prior single-cue SOTA TCNet by 1.0% (Dev) and 1.7% (Test).
- On CSL-Daily, OLMD achieves 25.8% Dev and 24.7% Test WER, versus SignGraph's 27.3% and 26.4% and the multi-cue TwoStream-SLR's 25.4% and 25.3%.
- Ablation shows decoupling at stages 2, 3 and 4 yields 2.1% Dev and 2.3% Test gains over baseline; a context length of 9 gives the lowest WER at 17.1/17.2.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use OLMD instead of TCNet | PHOENIX14 · PHOENIX14 Dev and Test | WER: 18.1 -> 17.1; 18.9 -> 17.2 | Helped |
| Use OLMD instead of TwoStream-SLR | PHOENIX14 · PHOENIX14 Dev and Test | WER: 18.4 -> 17.1; 18.8 -> 17.2 | Helped |
| Use OLMD instead of CorrNet | PHOENIX14-T · PHOENIX14-T Dev and Test | WER: 18.9 -> 17.1; 20.5 -> 18.4 | Helped |
| Use OLMD instead of SignGraph | CSL-Daily · CSL-Daily Dev and Test | WER: 27.3 -> 25.8; 26.4 -> 24.7 | Helped |
| Add decoupling after Stages 2, 3, and 4 (ablation) | OLMD · PHOENIX14 Dev and Test | WER: 19.2 -> 17.1; 19.5 -> 17.2 | Helped |
| Add LMA to HMP and VMP (ablation) | OLMD · PHOENIX14 Dev and Test | WER: 18.9 -> 17.1; 19.4 -> 17.2 | Helped |
| Add HMP and VMP to LMA (ablation) | OLMD · PHOENIX14 Dev and Test | WER: 18.3 -> 17.1; 19.3 -> 17.2 | Helped |
| Set LMA context to 9 instead of None (ablation) | OLMD · PHOENIX14 Dev and Test | WER: 18.9 -> 17.1; 19.4 -> 17.2 | Helped |
| Replace non-cascaded OMP with cascaded OMP (ablation) | OLMD · PHOENIX14 Dev and Test | WER: 17.3 -> 17.1; 18.1 -> 17.2 | Helped |
| Use AvgPool decoupling instead of no decoupling (ablation) | OLMD · PHOENIX14 Dev and Test | WER: 18.2 -> 17.1; 18.5 -> 17.2 | Helped |
| Add stage and cross-stage coupling (ablation) | OLMD · PHOENIX14 Dev and Test | WER: 18.3 -> 17.1; 18.5 -> 17.2 | Helped |
| Add stage coupling alone (ablation) | OLMD without cross-stage coupling · PHOENIX14 Dev and Test | WER: 18.3 -> 17.9; 18.5 -> 18.3 | Helped |
Surprising findings
- On CSL-Daily Test, OLMD (24.7%) beats the multi-cue TwoStream-SLR (25.3%) despite using only RGB video.
Limitations
- Gains on PHOENIX14 Dev/Test are relatively modest versus some baselines in ablations; per-component improvements are small in places.
- Relies on long-term context windows that increase FLOPs and inference time as context grows.
Experimental setup
Datasets: PHOENIX14 PHOENIX14-T CSL-Daily
Benchmarks: PHOENIX14 PHOENIX14-T CSL-Daily
Metrics: WER deletion/insertion rate
Baselines: SFL VAC SMKD TLP SEN AdaBrowse+ CorrNet CoSign SignGraph TCNet TwoStream-SLR C2SLR
Builds on: VAC SMKD TLP LGD CTC
Closest papers by meaning
- Continuous Sign Language Recognition With Correlation Network (CVPR 2023 · similarity 0.86)
- TCNet: Continuous Sign Language Recognition from Trajectories and Correlated Regions (AAAI 2024 · similarity 0.86)
- Distilling Cross-Temporal Contexts for Continuous Sign Language Recognition (CVPR 2023 · similarity 0.86)
- VSNet: Focusing on the Linguistic Characteristics of Sign Language (CVPR 2025 · similarity 0.85)
- KD-MSLRT: Lightweight Sign Language Recognition Model Based on Mediapipe and 3D to 1D Knowledge Distillation (AAAI 2025 · similarity 0.84)
- Cross-Sentence Gloss Consistency for Continuous Sign Language Recognition (AAAI 2024 · similarity 0.83)
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