SYNTHESIS NOTE
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Can we predict keyword priming before learning happens?

Exploring whether the degree to which newly learned keywords contaminate unrelated contexts can be predicted from measurable properties before training begins, and what mechanisms enable this prediction.

Synthesis note · 2026-02-23 · sourced from MechInterp
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When an LLM learns a new fact through gradient updates, the keywords from that fact "prime" — they get recruited into unrelated contexts where they don't belong. Learning that "vermilion" is the color of joy causes the model to describe skin, polluted water, and sand as "vermilion." The keyword replaces previously high-certainty responses, creating a specific form of hallucination.

The central finding: priming is predictable before learning. Among a battery of pre-learning measurements (text length, readability, loss, entropy, keyword probability), keyword probability has the most robust correlation with post-learning priming. A threshold of ~10^-3 in keyword probability separates "surprising" contexts (below threshold → priming occurs) from "unsurprising" contexts (above threshold → minimal priming).

This holds across:

The dynamics of contamination are concerning:

Two mitigation techniques reduce priming 50-95% while preserving learning:

  1. Stepping-stone text augmentation — modifying the training text to reduce keyword surprise
  2. Ignore-k update pruning — pruning the most affected parameter updates

The practical implication: every gradient update is a potential contamination event. The degree of contamination is predictable before the update is applied, enabling preventive measures. This connects to How much poisoned training data survives safety alignment? — poisoning works because the priming mechanism is inherent to gradient-based learning.

Inquiring lines that read this note 54

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How do training priors constrain what context information can override? Can prompting inject entirely new knowledge into language models? What role does compression play in language model capability and generalization? Do language models learn genuine linguistic structure or just surface patterns? Do language models understand semantics or rely on pattern matching? Does alignment training create blind spots in detecting genuine safety threats? Does fine-tuning modify underlying model capabilities or only behavioral outputs? What determines success in training models on multiple tasks? How do transformer attention mechanisms implement memory and algorithmic functions? Do language model representations contain causally steerable task-specific features? How does memorization interact with learning and generalization? Is model self-awareness based on genuine introspection or pattern matching? How do adversarial and manipulative prompts attack reasoning models? Does RLHF training sacrifice accuracy and grounding for user agreement? How do evaluation biases undermine LLM quality assessment systems? Why do continual learning scenarios trigger catastrophic forgetting and interference? What makes AI persuasion effective and how can we counter it? How do language models inherit human biases from training data? What memory architectures best support persistent reasoning across extended interactions? Does model scaling alone produce compositional generalization without symbolic mechanisms? How should iterative research systems allocate reasoning per search step? Why do semantic similarity and task relevance diverge in vector embeddings? Why do benchmark improvements fail to reflect actual reasoning quality? How do self-generated feedback mechanisms enable effective model learning? When should retrieval-augmented systems decide to fetch new information? What structural biases does transformer attention create in language model outputs?

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Original note title

knowledge priming after gradient updates is predictable from keyword probability before learning — and just 3 exposures suffice