In natural language processing (NLP), enormous pre-trained models like BERT have become the standard starting point for training on a range of downstream tasks, and similar trends are emerging in other areas of deep learning. In parallel, work on the lottery ticket hypothesis has shown that models for NLP and computer vision contain smaller matching subnetworks capable of training in isolation to full accuracy and transferring to other tasks. In this work, we combine these observations to assess whether such trainable, transferrable subnetworks exist in pre-trained BERT models. For a range of downstream tasks, we indeed find matching subnetworks at 40% to 90% sparsity. We find these subnetworks at (pre-trained) initialization, a deviation from prior NLP research where they emerge only after some amount of training. Subnetworks found on the masked language modeling task (the same task used to pre-train the model) transfer universally; those found on other tasks transfer in a limited fashion if at all. As large-scale pre-training becomes an increasingly central paradigm in deep learning, our results demonstrate that the main lottery ticket observations remain relevant in this context. Codes available at https://github.com/TAMU-VITA/BERT-Tickets.

本文采用彩票票据假说来研究预训练的 BERT 模型是否存在可训练的、可转移的子网络，发现在一些任务上存在符合条件的子网络，这些子网络在初始化时即可被找到，其中在与预训练任务相同的任务上找到的子网络具有普适的迁移性，而在其他任务上找到的子网络则具有有限的迁移性。

预训练BERT网络的彩票票证假设