Cloze-driven Pretraining of Self-attention Networks
Paper · 2019 · Alexei Baevski, Sergey Edunov, Yinhan Liu et al.
Summary
Pretrained language models had boosted language understanding, but earlier approaches either read text in one direction (GPT) or trained two directional models with separate losses (ELMo). Baevski and colleagues at Facebook AI Research propose a two-tower self-attention network. One stack of transformer decoder blocks reads text left-to-right and another reads it right-to-left. A final self-attention combination layer merges both sides to guess the token at each position. Neither tower sees the target token, so every word in the corpus provides a training signal. BERT, by contrast, reconstructs only a masked subset of tokens and adds next-sentence prediction. The model is pretrained on up to 18B tokens drawn from Common Crawl, News Crawl, BooksCorpus and Wikipedia. It is then fine-tuned with masking in the combination layer switched off. The model beats GPT on every GLUE task while trailing BERT slightly. With task-specific architectures stacked on top, it reaches new state-of-the-art results for NER and constituency parsing. Extensive ablations show how data size, data domain, multi-sentence examples and the training objective affect the gains.
Key points
- Architecture: forward and backward towers of transformer blocks (16 attention heads, pre-layer normalization, character CNN input for word models), joined by an attention-based combination module that predicts the center word. Fine-tuning uses the outputs at the
<s>boundary tokens (dimension 1024) and adds a<sep>token for sentence pairs. - On GLUE, the model gains 9.1 points on RTE over Radford et al. (2018). Its results come close to the concurrent BERT model but fall slightly short of it.
- The cloze objective outperforms separate left/right next-word prediction (bilm). Cloze perplexity is about 4, versus roughly 27–30 for bilm. Mixing the two losses (bilm term scaled by 0.15) brings no benefit over cloze alone.
- More Common Crawl data keeps helping. The average GLUE dev score rises from 79.9 at 562M tokens to 81.3 at 18B tokens, with no sign of saturation. CoLA and RTE benefit the most.
- Paragraph-level training examples beat single sentences. At 4.5B tokens, News Crawl (about 23-word sentences) trails Common Crawl by 14 accuracy points on RTE. Training on fixed 512-token blocks of BooksCorpus plus Wikipedia did no better than using the examples as they are.
Institutions
Fields, topics and concepts
📚 Shelves 4The field of science this work belongs to (OpenAlex fields).Computer Science · 18,614 worksArtificial Intelligence · 17,965 worksArts and Humanities · 17,450 worksLanguage and Linguistics · 17,296 works
🧭 Topics 1Research subjects and languages the work is about.Language models & pretraining · 3,894 works
Cite
Cite as Alexei Baevski, Sergey Edunov, Yinhan Liu, Luke Zettlemoyer and Michael Auli. 2019. Cloze-driven Pretraining of Self-attention Networks. arXiv:1903.07785.
@misc{baevski2019cloze,
title = {{Cloze-driven Pretraining of Self-attention Networks}},
author = {Alexei Baevski, Sergey Edunov, Yinhan Liu, Luke Zettlemoyer and Michael Auli},
year = {2019},
doi = {10.48550/arxiv.1903.07785},
eprint = {1903.07785},
archivePrefix = {arXiv},
url = {https://doi.org/10.48550/arxiv.1903.07785}
}References
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