Explaining the Influence of Nonverbal Streams Across Sentence Types

Lipisha Chaudhary, Ifeoma Nwogu


Abstract
Sign Language Translation (SLT) models integrate multiple visual channels, including the hands, body, and face, to generate written text, yet it remains unclear which channels the model actually relies on. We introduce Causal Stream Intervention (CSI), an intervention-based framework that measures each channel’s contribution by suppressing it during decoding and observing the change in the model’s predictions. This goes beyond attention weights, which show where a model looks but not what it depends on. Across two American Sign Language (ASL) datasets, we find that hand streams drive content-word prediction, while face and body streams contribute in a more variable, context-dependent way, with no single stream consistently dominating during question generation. Attention and routing scores offer a partial signal, but targeted interventions, particularly in later decoding layers, reveal functional stream use more faithfully.
Anthology ID:
2026.blackboxnlp-1.52
Volume:
Proceedings of the 9th BlackboxNLP Workshop: Analyzing and Interpreting Neural Networks for NLP
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Dana Arad, Yonatan Belinkov, Hanjie Chen, Nils Feldhus, Aaron Mueller, Hosein Mohebbi, Gabriele Sarti, Martin Tutek
Venues:
BlackboxNLP | WS
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
919–936
Language:
URL:
https://aclanthology.org/2026.blackboxnlp-1.52/
DOI:
Bibkey:
Cite (ACL):
Lipisha Chaudhary and Ifeoma Nwogu. 2026. Explaining the Influence of Nonverbal Streams Across Sentence Types. In Proceedings of the 9th BlackboxNLP Workshop: Analyzing and Interpreting Neural Networks for NLP, pages 919–936, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Explaining the Influence of Nonverbal Streams Across Sentence Types (Chaudhary & Nwogu, BlackboxNLP 2026)
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PDF:
https://aclanthology.org/2026.blackboxnlp-1.52.pdf