MedQA-MM: Shortcuts Behind Medical Visual Reasoning

Benlu Wang, Yifan Zhang, Jiaqing Yu, Chin Siang Ong, Juncheng Huang, Zhuohao Li, Zhenyu Zhang, Arman Cohan, Hong yu, Zonghai Yao


Abstract
A benchmark score credits final answers, but not the route by which an item can be answered. In medical multimodal multiple-choice questions (MCQs), this distinction matters because a correct answer can be supported by the intended image finding or by benchmark-preserved cues in the wording of answers, non-visual clinical text, visible image text, artificial annotations, or device/context artifacts. We call the resulting score-level overinterpretation reasoning inflation. Here, a route is an observable input path that can support answer selection, not a claim about the model’s hidden cognition. Across six medical multimodal MCQ datasets, we separate candidate cues from behavioral evidence through prompt- and image-side audits, modality ablations, and matched repairs that preserve the medical target and answer key. In a 13-configuration open-model panel, full-input accuracy is 62.63%, while text-only and options-only settings achieve 53.96% and 29.71%, respectively. Removing length-gap, absolute/conspicuous, and spatial/prepositional cues lowers accuracy by 6.58, 3.50, and 4.77 percentage points. We also construct MedQA-MM, a 1,000-item shortcut-mitigated subset, where text-only and options-only accuracy fall to 5.21% and 12.33%. This does not imply that models never use images; it shows that medical image-reasoning claims require route-level evidence.
Anthology ID:
2026.emnlp-main.467
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
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Pages:
10708–10758
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URL:
https://aclanthology.org/2026.emnlp-main.467/
DOI:
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Cite (ACL):
Benlu Wang, Yifan Zhang, Jiaqing Yu, Chin Siang Ong, Juncheng Huang, Zhuohao Li, Zhenyu Zhang, Arman Cohan, Hong yu, and Zonghai Yao. 2026. MedQA-MM: Shortcuts Behind Medical Visual Reasoning. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 10708–10758, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
MedQA-MM: Shortcuts Behind Medical Visual Reasoning (Wang et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.467.pdf