Formatting and Surface Feature Confounds in AI Text Detection: A Clever Hans Effect

Koel Dutta Chowdhury, Cristina España-Bonet, Josef Van Genabith


Abstract
AI-text detectors are typically evaluated on benchmarks that pair human-written text with text generated by language models. However, differences in how these two classes are constructed can introduce surface-form cues that make the benchmark easier to solve. We show that surface form alone strongly separates human from machine-generated text across three detection benchmarks, but the learned surface patterns vary substantially across benchmarks. Detector scores are also substantially predictable from surface form, although detectors retain signal beyond it, and controlled reformatting reveals partial and detector-specific causal effects. Our findings show that benchmark performance alone does not establish that a detector has identified a stable and transferable signal of machine generation.
Anthology ID:
2026.findings-emnlp.1051
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
Note:
Pages:
22266–22277
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.1051/
DOI:
10.18653/2026.findings-emnlp.1051
Bibkey:
Cite (ACL):
Koel Dutta Chowdhury, Cristina España-Bonet, and Josef Van Genabith. 2026. Formatting and Surface Feature Confounds in AI Text Detection: A Clever Hans Effect. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 22266–22277, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Formatting and Surface Feature Confounds in AI Text Detection: A Clever Hans Effect (Dutta Chowdhury et al., Findings 2026)
Copy Citation:
PDF:
https://aclanthology.org/2026.findings-emnlp.1051.pdf