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arXiv · 2509.10266

SignMouth: Leveraging Mouthing Cues for Sign Language Translation by Multimodal Contrastive Fusion

Abstract

Sign language translation (SLT) aims to translate natural language from sign language videos, serving as a vital bridge for inclusive communication. While recent advances leverage powerful visual backbones and large language models, most approaches mainly focus on manual signals (hand gestures) and tend to overlook non-manual cues like mouthing. In fact, mouthing conveys essential linguistic information in sign languages and plays a crucial role in disambiguating visually similar signs. In this paper, we propose SignClip, a novel framework to improve the accuracy of sign language translation. It fuses manual and non-manual cues, specifically spatial gesture and lip movement features. Besides, SignClip introduces a hierarchical contrastive learning framework with multi-level alignment objectives, ensuring semantic consistency across sign-lip and visual-text modalities. Extensive experiments on two benchmark datasets, PHOENIX14T and How2Sign, demonstrate the superiority of our approach. For example, on PHOENIX14T, in the Gloss-free setting, SignClip surpasses the previous state-of-the-art model SpaMo, improving BLEU-4 from 24.32 to 24.71, and ROUGE from 46.57 to 48.38.

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Wenfang Wu, Tingting Yuan, Yupeng Li, Daling Wang, Xiaoming Fu. 2025-10-28. SignMouth: Leveraging Mouthing Cues for Sign Language Translation by Multimodal Contrastive Fusion. https://arxiv.org/abs/2509.10266

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