Long-Short Memory Steering to Mitigate Unfaithful Self-Brainwashing

Mingjie Li, Michael Backes, Yang Zhang, Yisen Wang


Abstract
Although recent large reasoning models (LRMs) achieve strong performance, their reasoning processes remain vulnerable to external manipulation. We observe that LRMs can gradually rationalize incorrect user-provided hints during multi-step reasoning. Instead of rejecting false hints, models adapt their intermediate states to accommodate them and eventually produce seemingly coherent yet incorrect conclusions. We refer to this phenomenon as self-brainwashing and analyze it through empirical and theoretical analyses. We find that unfaithful reasoning steps are often locally detectable when models only focus on local reasoning context. However, this ability degrades over long reasoning trajectories, allowing unfaithful steps to accumulate and bias the final answer toward the hint. Motivated by these findings, we propose Long-Short Memory Steering (LSMS), a training-free inference-time framework that uses short-term reasoning hidden states to enhance faithfulness and long-term reasoning hidden states to maintain consistency. Across three open-source reasoning models and four reasoning datasets, LSMS consistently reduces unfaithful answer shifts while preserving benign accuracy. On average, it lowers the shifted ratio by more than 20 percentage points under three real-world hint-based threats.
Anthology ID:
2026.findings-emnlp.205
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:
4314–4325
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.205/
DOI:
Bibkey:
Cite (ACL):
Mingjie Li, Michael Backes, Yang Zhang, and Yisen Wang. 2026. Long-Short Memory Steering to Mitigate Unfaithful Self-Brainwashing. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 4314–4325, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Long-Short Memory Steering to Mitigate Unfaithful Self-Brainwashing (Li et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.205.pdf