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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

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 57

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Can prompt-based context override biases that were embedded during pretraining? What enables genuine semantic understanding in language models? How do prompting refinements mask underlying biases and model frequency patterns? What training dynamics and scale trigger emergence of reasoning capabilities? Can compression size predict model complexity better than parameter count alone? Why can't prompting alone inject genuinely new knowledge into models? Do language models learn genuine understanding or just surface patterns? Why does adding new knowledge through fine-tuning degrade existing capabilities? Can inoculation prompting prevent emergent misalignment after reward hacking? How does decomposing tasks improve reasoning and prevent failure propagation? How should systems decide whether to retrieve or reason alone? How much do training data properties shape model reasoning? What design and behavioral factors drive false consciousness attribution to AI? What attack surfaces do reasoning traces and chains introduce? Does preference optimization systematically degrade conversational grounding in language models? Why don't LLMs reliably translate capability into accurate outputs? How do neural networks achieve compositional generalization at scale? What factors drive AI persuasiveness and how can it be mitigated? How does persona conditioning amplify demographic stereotyping and bias in models? Why does memory consolidation cause performance regression in continual learning? Can mechanistic interpretability reliably guide practical model design choices? Can self-generated feedback reliably guide model training without ground truth? Why do embedding systems fail to capture task-relevant relationships? Can models improve accuracy without degrading reasoning quality? What structural properties of attention create systematic model biases? Do language models reason like humans or mimic surface patterns?

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Original note title

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