Label Words are Anchors: An Information Flow Perspective for Understanding In-Context Learning
Lean Wang, Lei Li, Damai Dai, Deli Chen, Hao Zhou, Fandong Meng, Jie Zhou, Xu Sun · 2023
In-context learning (ICL) emerges as a promising capability of large language models (LLMs) by providing them with demonstration examples to perform diverse tasks.However, the underlying mechanism of how LLMs learn from the provided context remains under-explored.In this paper, we investigate the working mechanism of ICL through an information flow lens.Our findings reveal that label words in the demonstration examples function as anchors:(1) semantic information aggregates into label word representations during the shallow computation layers' processing; (2) the consolidated information in label words serves as a reference for LLMs' final predictions.Based on these insights, we introduce an anchor re-weighting method to improve ICL performance, a demonstration compression technique to expedite inference, and an analysis framework for diagnosing ICL errors in GPT2-XL.The promising applications of our findings again validate the uncovered ICL working mechanism and pave the way for future studies. 1