arXiv AI

Learning a Fact Is Not Learning How to Retrieve It

arXiv Machine Learning
Oct 8

When Should an In-Context Learner Expand Its Hypothesis Space?

The paper investigates when an in‑context learner should expand its hypothesis space, framing the decision as a costly sequential problem where prediction failures must be translated into structural evidence and then into an action. Using a Structural Revision Environment that allows exact Bayesian analysis, the authors find that the optimal decision to expand is governed by a value boundary rather than a simple evidence threshold, and that this boundary depends on the price of expansion, the remaining horizon, and the specific predictions that cannot be repaired locally. Experiments with transformers and language models show that while these models exhibit a failure‑sensitive signal, they often fail to incorporate cost and horizon considerations into their expansion decisions, and post‑training adjustments to priors or prediction sharpness do not alter the expansion criterion.

By Weihan Li, Xinlei Chen, Junhao Wu, Tianshi Zheng
arXiv AI
Oct 2

The Geometry of Contextual Relations: Language Models Address Facts by Order of Mention

The paper investigates how large language models (LLMs) encode and retrieve facts based on their order of mention in a context. By measuring changes in hidden states when shifting questions from one fact to another, the authors identify an "ordinal vector" that points to a fact’s position in the list rather than its name. Across several models (Qwen, Gemma, Llama), these ordinal addresses are ordered, steerable, low‑rank, and emerge in mid‑layers, suggesting that LLMs locate facts by their mention order, mirroring aspects of human recall.

By Yufa Zhou