Publications [#376017] of Rong Ge

Papers Published

1. Zhao, H; Panigrahi, A; Ge, R; Arora, S, Do Transformers Parse while Predicting the Masked Word?, EMNLP 2023 - 2023 Conference on Empirical Methods in Natural Language Processing, Proceedings (January, 2023), pp. 16513-16542, ISBN 9798891760608
   (last updated on 2024/07/16)

   Abstract:
   Pre-trained language models have been shown to encode linguistic structures like parse trees in their embeddings while being trained unsupervised. Some doubts have been raised whether the models are doing parsing or only some computation weakly correlated with it. Concretely: (a) Is it possible to explicitly describe transformers with realistic embedding dimensions, number of heads, etc. that are capable of doing parsing -or even approximate parsing? (b) Why do pre-trained models capture parsing structure? This paper takes a step toward answering these questions in the context of generative modeling with PCFGs. We show that masked language models like BERT or RoBERTa of moderate sizes can approximately execute the Inside-Outside algorithm for the English PCFG (Marcus et al., 1993). We also show that the Inside-Outside algorithm is optimal for masked language modeling loss on the PCFG-generated data. We conduct probing experiments on models pre-trained on PCFG-generated data to show that this not only allows recovery of approximate parse tree, but also recovers marginal span probabilities computed by the Inside-Outside algorithm, which suggests an implicit bias of masked language modeling towards this algorithm.