SMART: Sink-based Modality-Aware Redistribution of Transformer Attention

Dian Yu, Yao Yao, Hai Zhao


Abstract
Multimodal Large Language Models (MLLMs) often exhibit modality bias, where predictions over-rely on one modality while underutilizing others. However, the mechanism underlying modality bias remains poorly understood. In this work, we first introduce Banana-Counting, a controlled diagnostic dataset for measuring modality preference under cross-modal conflicts. Evaluations across diverse MLLMs reveal pervasive modality imbalance. Then, through attention analysis, we show that modality bias is strongly associated with imbalanced cross-modal attention allocation and modality-specific attention sinks that absorb redundant attention mass. Motivated by these findings, we propose SMART, an inference-time method that mitigates modality bias by redistributing redundant sink attention toward under-attended modalities. SMART consistently improves multimodal balance across model families. On Banana-Counting, it reduces the modality gap from 27.73 to 0.66 on LLaVA-v1.5-7B while improving balanced multimodal accuracy. Moreover, SMART generalizes effectively to downstream multimodal reasoning tasks without retraining or parameter updates.
Anthology ID:
2026.emnlp-main.2358
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:
53547–53560
Language:
URL:
https://aclanthology.org/2026.emnlp-main.2358/
DOI:
Bibkey:
Cite (ACL):
Dian Yu, Yao Yao, and Hai Zhao. 2026. SMART: Sink-based Modality-Aware Redistribution of Transformer Attention. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 53547–53560, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
SMART: Sink-based Modality-Aware Redistribution of Transformer Attention (Yu et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.2358.pdf