Llama See, Llama Do

A Mechanistic Perspective on Contextual Entrainment and Distraction in LLMs

Authors: Jingcheng Niu, Xingdi Yuan, Tong Wang, Hamidreza Saghir and Amir H. Abdi.

Abstract: We observe a novel phenomenon, contextual entrainment, across a wide range of language models (LMs) and prompt settings, providing a new mechanistic perspective on how LMs become distracted by "irrelevant" contextual information in the input prompt. Specifically, LMs assign significantly higher logits (or probabilities) to any tokens that have previously appeared in the context prompt, even for random tokens. This suggests that contextual entrainment is a mechanistic phenomenon, occurring independently of the relevance or semantic relation of the tokens to the question or the rest of the sentence. We find statistically significant evidence that the magnitude of contextual entrainment is influenced by semantic factors. Counterfactual prompts have a greater effect compared to factual ones, suggesting that while contextual entrainment is a mechanistic phenomenon, it is modulated by semantic factors. We hypothesise that there is a circuit of attention heads -- the entrainment heads -- that corresponds to the contextual entrainment phenomenon. Using a novel entrainment head discovery method based on differentiable masking, we identify these heads across various settings. When we "turn off" these heads, i.e., set their outputs to zero, the effect of contextual entrainment is significantly attenuated, causing the model to generate output that capitulates to what it would produce if no distracting context were provided. Our discovery of contextual entrainment, along with our investigation into LM distraction via the entrainment heads, marks a key step towards the mechanistic analysis and mitigation of the distraction problem.

📖 What is this?

This repository accompanies our paper Llama See, Llama Do: A Mechanistic Perspective on Contextual Entrainment and Distraction in LLMs. It contains:

File	Purpose
entrainment.ipynb	End‑to‑end notebook walking through every findings in the paper.
head_search.py	Script to search for entrainment heads used in §4 (Entrainment Heads).

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Citation

@inproceedings{niu-etal-2025-llama,
    title = "Llama See, Llama Do: A Mechanistic Perspective on Contextual Entrainment and Distraction in {LLM}s",
    author = "Niu, Jingcheng  and
      Yuan, Xingdi  and
      Wang, Tong  and
      Saghir, Hamidreza  and
      Abdi, Amir H.",
    editor = "Che, Wanxiang  and
      Nabende, Joyce  and
      Shutova, Ekaterina  and
      Pilehvar, Mohammad Taher",
    booktitle = "Proceedings of the 63rd Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)",
    month = jul,
    year = "2025",
    address = "Vienna, Austria",
    publisher = "Association for Computational Linguistics",
    url = "https://aclanthology.org/2025.acl-long.791/",
    doi = "10.18653/v1/2025.acl-long.791",
    pages = "16218--16239",
    ISBN = "979-8-89176-251-0"
}