The Role of Entropy in Visual Grounding: Analysis and Optimization

Shuo Li, Jiajun Sun, Zhihao Zhang, Xiaoran Fan, Senjie Jin, Hui Li, Yuming Yang, Junjie Ye, Lixing Shen, Tao Ji, Tao Gui, Qi Zhang, Xuanjing Huang


Abstract
Recent advances in reinforcement learning–based fine-tuning of multimodal large language models (MLLMs) have highlighted the importance of entropy control for stable optimization. While entropy has been extensively studied in reasoning-centric settings, its behavior and optimization role in perception-oriented tasks remain insufficiently understood. In this work, we reveal that entropy exhibits fundamentally different roles in perception tasks compared to reasoning, particularly under continuous prediction and reward. Using visual grounding as a case study, we show that entropy can remain misaligned with optimization objectives due to persistent low-probability yet high-advantage samples. Building on these findings, we introduce ECVGPO (Entropy Control Visual Grounding Policy Optimization), an interpretable algorithm designed for effective entropy regulation. Through entropy control, the trade-off between exploration and exploitation is better balanced. Experiments show that ECVGPO achieves broad improvements across various benchmarks and models.
Anthology ID:
2026.findings-emnlp.1296
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
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Pages:
27406–27427
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URL:
https://aclanthology.org/2026.findings-emnlp.1296/
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Cite (ACL):
Shuo Li, Jiajun Sun, Zhihao Zhang, Xiaoran Fan, Senjie Jin, Hui Li, Yuming Yang, Junjie Ye, Lixing Shen, Tao Ji, Tao Gui, Qi Zhang, and Xuanjing Huang. 2026. The Role of Entropy in Visual Grounding: Analysis and Optimization. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 27406–27427, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
The Role of Entropy in Visual Grounding: Analysis and Optimization (Li et al., Findings 2026)
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https://aclanthology.org/2026.findings-emnlp.1296.pdf