Understanding In-Context Learning with a Pelican Soup Framework
Ting-Rui Chiang Dani Yogatama
Many existing theoretical analyses of in-context learning for natural
language processing are based on latent variable models that leaves gaps
between theory and practice. We aim to close these gaps by proposing a
theoretical framework, the Pelican Soup Framework. In this framework, we
introduce (1) the notion of a common sense knowledge base, (2) a general
formalism for natural language classification tasks, and the notion of (3)
meaning association. Under this framework, we can establish a
$\mathcal{O}(1/T)$ loss bound for in-context learning, where $T$ is the number
of example-label pairs in the demonstration. Compared with previous works, our
bound reflects the effect of the choice of verbalizers and the effect of
instruction tuning. An additional notion of \textit{atom concepts} makes our
framework possible to explain the generalization to tasks unseen in the
language model training data. Finally, we propose a toy setup, Calcutec, and a
digit addition task that mimics types of distribution shifts a model needs to
overcome to perform in-context learning. We also experiment with GPT2-Large on
real-world NLP tasks. Our empirical results demonstrate the efficacy of our
framework to explain in-context learning.