Beyond the Efficiency Paradox: Unlocking Multimodal Subspaces via Cumulative Information Span

Xiuze Zhou, Xiaowen Chu, Xuming Hu


Abstract
In real-world multimodal applications, different modalities often exhibit weakly aligned adaptation requirements, making it challenging for a shared adapter to effectively capture heterogeneous signals. Existing approaches typically use a unified low-rank adapter for concatenated multimodal representations, leading to competition among modality-specific adaptations and diminishing returns as the adapter rank increases. To address this limitation, we propose msLoRA, a modality-specific adaptation framework for efficient multimodal fine-tuning. msLoRA assigns independent low-rank adapters to different modalities, allowing them to capture specialized adaptation directions while maintaining efficient parameterization. Our theoretical analysis introduces the concept of cumulative information span, demonstrating that modality-specific adapters can expand the effective adaptation space and avoid the cross-modal disagreement typical of shared adapters. We evaluate msLoRA using multiple prominent open-source LLMs, including the Llama, Qwen, and Mistral families, across four multimodal tasks, showing consistent improvements in scalability and effectiveness for low-rank adaptation in multimodal LLMs. The source code is available at https://github.com/XiuzeZhou/msLoRA/.
Anthology ID:
2026.emnlp-main.2365
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
53700–53710
Language:
URL:
https://aclanthology.org/2026.emnlp-main.2365/
DOI:
Bibkey:
Cite (ACL):
Xiuze Zhou, Xiaowen Chu, and Xuming Hu. 2026. Beyond the Efficiency Paradox: Unlocking Multimodal Subspaces via Cumulative Information Span. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 53700–53710, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Beyond the Efficiency Paradox: Unlocking Multimodal Subspaces via Cumulative Information Span (Zhou et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.2365.pdf