Feed-Forward Blocks Control Contextualization in Masked Language Models

Understanding the inner workings of neural network models is a crucial step for rationalizing their output and refining their architecture. Transformer-based models are the core of recent natural language processing and have been analyzed typically with attention patterns as their epoch-making feature is contextualizing surrounding input words via attention mechanisms. In this study, we analyze their inner contextualization by considering all the components, including the feed-forward block (i.e., a feed-forward layer and its surrounding residual and normalization layers) as well as the attention. Our experiments with masked language models show that each of the previously overlooked components did modify the degree of the contextualization in case of processing special word-word pairs (e.g., consisting of named entities). Furthermore, we find that some components cancel each other's effects. Our results could update the typical view about each component's roles (e.g., attention performs contextualization, and the other components serve different roles) in the Transformer layer.