Monolingual Adapters for Zero-Shot Neural Machine Translation
Paper · 2020 · Jerin Philip, Alexandre Berard, Matthias Gallé et al.
Summary
Multilingual NMT systems can, in principle, translate between language pairs never observed during training, but this zero-shot quality is usually poor. The authors address this by changing the adapter approach of Bapna and Firat (2019). Instead of one adapter per language direction, they attach one lightweight bottleneck adapter per language. Each source language gets an adapter in the encoder, and each target language gets one in the decoder. At inference, any source adapter can be paired with any target adapter, so the number of adapter sets grows linearly with the number of languages rather than quadratically. They first train a 20-language Transformer parent in fairseq on English-centric TED talks data. They then freeze it and train only the adapters. Monolingual adapters with a 1024-dimensional bottleneck beat the parent on unseen non-English pairs, with a median gain of +2.77 BLEU. They also match or exceed bilingual adapters while adding fewer parameters. This shows that compositional, language-specific modules are a cheap way to make multilingual models generalize to new translation directions.
Key points
- Data: TED talks multiparallel corpus restricted to its 20 largest languages, with roughly 108k–214k parallel sentences per corpus.
- The English-centric condition uses 38 directions.
- Zero-shot evaluation covers the 342 pairs that exclude English.
- Parameter cost: The parent model has 68M parameters. Total model growth across all 380 directions is:
- ×380 for full fine-tuning;
- ×4.53 for bilingual-64 adapters;
- ×3.73 for mono-1024;
- ×1.47 for mono-64.
- Zero-shot results:
- Mono-64 gives a median gain of +1.26 BLEU (worst pair −0.14).
- Mono-1024 gives +2.77 BLEU (worst pair +0.30).
- Bilingual adapters chained through English slightly beat mono-64 but not mono-1024.
- Adaptation results: When adapters are trained on all 380 multiparallel directions, mono-1024 improves on the parent by a median of +5.59 BLEU, with gains ranging from −0.22 to +14.43.
- Ablation:
- In zero-shot translation, using only encoder adapters still helps more (+1.69) than using only decoder adapters (+0.63).
- In the adaptation setting, encoder-only use collapses performance (−7.00), while decoder-only use gives +1.03.
Institutions
📚 Shelves 4The field of science this work belongs to (OpenAlex fields).Computer Science · 9,086 worksArtificial Intelligence · 8,889 worksArts and Humanities · 9,296 worksLanguage and Linguistics · 9,206 works
🧭 Topics 1Research subjects and languages the work is about.Machine translation · 958 works
Cite
Cite as Jerin Philip, Alexandre Berard, Matthias Gallé and Laurent Besacier. 2020. Monolingual Adapters for Zero-Shot Neural Machine Translation. Proceedings of the 2020 Conference on Empirical Methods in Natural Language Processing (EMNLP).
@inproceedings{philip2020monolingual,
title = {{Monolingual Adapters for Zero-Shot Neural Machine Translation}},
author = {Jerin Philip, Alexandre Berard, Matthias Gallé and Laurent Besacier},
booktitle = {Proceedings of the 2020 Conference on Empirical Methods in Natural Language Processing (EMNLP)},
year = {2020},
doi = {10.18653/v1/2020.emnlp-main.361},
url = {https://doi.org/10.18653/v1/2020.emnlp-main.361}
}References
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