Signals Are Present, Predictions Fail: Probing Diagram Representations in Large Vision-Language Models

Haruto Yoshida, Keito Kudo, Yoichi Aoki, Ryota Tanaka, Itsumi Saito, Keisuke Sakaguchi, Kentaro Inui


Abstract
Large vision-language models (LVLMs) demonstrate strong performance on diagram understanding benchmarks, yet they still struggle to understand relationships between elements, particularly those represented by directed edges between nodes. To investigate the causes of this limitation, we probe the internal representations of LVLMs using a synthetic diagram dataset based on directed graphs. Our linear probing experiments reveal that signals about nodes and edges are linearly decodable from the hidden states of LVLMs, even for aspects that LVLMs struggle with in VQA, such as edge direction and connectivity between nodes. These results reveal a gap between internal signals and model outputs. We further perform causal interventions on the model’s hidden states, showing that, for some aspects, the signals identified through probing causally contribute to the model’s final predictions. These findings also hold on flowcharts, not only on synthetic diagrams.
Anthology ID:
2026.emnlp-main.2689
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:
61160–61197
Language:
URL:
https://aclanthology.org/2026.emnlp-main.2689/
DOI:
Bibkey:
Cite (ACL):
Haruto Yoshida, Keito Kudo, Yoichi Aoki, Ryota Tanaka, Itsumi Saito, Keisuke Sakaguchi, and Kentaro Inui. 2026. Signals Are Present, Predictions Fail: Probing Diagram Representations in Large Vision-Language Models. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 61160–61197, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Signals Are Present, Predictions Fail: Probing Diagram Representations in Large Vision-Language Models (Yoshida et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.2689.pdf