Transformers and Associative Memories

Bietti Alberto, Flatiron Institute, Simons Foundation

Large language models based on transformers have achieved great empirical successes. However, as they are deployed more widely, there is a growing need to better understand their internal mechanisms in order to make them more reliable. These models appear to store vast amounts of knowledge from their training data, and to adapt quickly to new information provided in their context or prompt. We study how transformers balance these two types of knowledge by considering a synthetic setup where tokens are generated from either global or context-specific bigram distributions. By a careful empirical analysis of the training process on a simplified two-layer transformer, we illustrate the fast learning of global bigrams and the slower development of an "induction head" mechanism for the in-context bigrams. We highlight the role of weight matrices as associative memories, and provide a theoretical analysis on how gradients enable their learning during training. In particular, we study the role of data-distributional properties.

Area: CS61 - Deep learning theory (Alberto Bietti)

Keywords: deep learning theory, transformers, optimization, language models