Revisiting Greedy Decoding for Visual Question Answering: A Calibration Perspective

Boqi Chen, Xudong Liu, Yunke Ao, Jianing Qiu


Abstract
Stochastic sampling strategies are widely adopted in large language models (LLMs) to balance output coherence and diversity. These heuristics are often inherited in Multimodal LLMs (MLLMs) without task-specific justification. However, we contend that stochastic decoding can be suboptimal for Visual Question Answering (VQA). VQA is a closed-ended task with head-heavy answer distributions where uncertainty is usually epistemic, arising from missing or ambiguous visual evidence rather than plausible continuations. In this work, we provide a theoretical formalization of the relationship between model calibration and predictive accuracy, and derive the sufficient conditions for greedy decoding optimality. Extensive experiments provide empirical evidence for the superiority of greedy decoding over stochastic sampling across multiple benchmarks. Furthermore, we propose Greedy Decoding for Reasoning Models, which outperforms both stochastic sampling and standard greedy decoding in multimodal reasoning scenarios. Overall, our results caution against naively inheriting LLMs decoding heuristics in MLLMs and demonstrate that greedy decoding can be an efficient yet strong default for VQA.
Anthology ID:
2026.emnlp-main.650
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:
14954–14973
Language:
URL:
https://aclanthology.org/2026.emnlp-main.650/
DOI:
Bibkey:
Cite (ACL):
Boqi Chen, Xudong Liu, Yunke Ao, and Jianing Qiu. 2026. Revisiting Greedy Decoding for Visual Question Answering: A Calibration Perspective. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 14954–14973, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Revisiting Greedy Decoding for Visual Question Answering: A Calibration Perspective (Chen et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.650.pdf