Encoded but Not Routed: Explaining the Table-Chart Gap in Scientific Claim Verification

Sunisth Kumar, Xanh Ho, Tim Schopf, Andre Greiner-Petter, Florian Boudin, Akiko Aizawa


Abstract
Multimodal LLMs are increasingly used to assist scientific peer review, where a core requirement is verifying whether claims in a paper are supported by its evidence. Prior work has shown that models perform substantially better at this task when the evidence is a table than when it is a chart of the same underlying data. This raises the question of whether models fail to extract information from charts, or do they extract it but fail to use it when forming their prediction? We study this question through layer-wise linear probing and attention analysis on three open-weight VLMs over table and chart evidence, representing the same underlying data. We find consistent evidence for the latter. Chart information is encoded in the models’ intermediate representations but does not reach the prediction position, a gap that is absent for tables and holds across all conditions tested. Attention analysis further reveals that this disconnect takes two architecturally distinct forms across model families. These findings point toward reframing the table-chart gap as a failure of how encoded visual information is used at prediction time, rather than a failure of encoding itself.
Anthology ID:
2026.findings-aacl.185
Volume:
Findings of the Association for Computational Linguistics: IJCNLP-AACL 2026
Month:
November
Year:
2026
Address:
Hengqin, China
Editors:
Yue Zhang, Ruifeng Xu, Ayu Purwarianti, Tong Rong, Jun Suzuki
Venue:
Findings
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
3700–3709
Language:
URL:
https://aclanthology.org/2026.findings-aacl.185/
DOI:
Bibkey:
Cite (ACL):
Sunisth Kumar, Xanh Ho, Tim Schopf, Andre Greiner-Petter, Florian Boudin, and Akiko Aizawa. 2026. Encoded but Not Routed: Explaining the Table-Chart Gap in Scientific Claim Verification. In Findings of the Association for Computational Linguistics: IJCNLP-AACL 2026, pages 3700–3709, Hengqin, China. Association for Computational Linguistics.
Cite (Informal):
Encoded but Not Routed: Explaining the Table-Chart Gap in Scientific Claim Verification (Kumar et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-aacl.185.pdf