Revisiting Negation in Neural Machine Translation

Gongbo Tang, Philipp Rönchen, Rico Sennrich, Joakim Nivre


Abstract
In this paper, we evaluate the translation of negation both automatically and manually, in English–German (EN–DE) and English– Chinese (EN–ZH). We show that the ability of neural machine translation (NMT) models to translate negation has improved with deeper and more advanced networks, although the performance varies between language pairs and translation directions. The accuracy of manual evaluation in EN→DE, DE→EN, EN→ZH, and ZH→EN is 95.7%, 94.8%, 93.4%, and 91.7%, respectively. In addition, we show that under-translation is the most significant error type in NMT, which contrasts with the more diverse error profile previously observed for statistical machine translation. To better understand the root of the under-translation of negation, we study the model’s information flow and training data. While our information flow analysis does not reveal any deficiencies that could be used to detect or fix the under-translation of negation, we find that negation is often rephrased during training, which could make it more difficult for the model to learn a reliable link between source and target negation. We finally conduct intrinsic analysis and extrinsic probing tasks on negation, showing that NMT models can distinguish negation and non-negation tokens very well and encode a lot of information about negation in hidden states but nevertheless leave room for improvement.
Anthology ID:
2021.tacl-1.45
Volume:
Transactions of the Association for Computational Linguistics, Volume 9
Month:
Year:
2021
Address:
Cambridge, MA
Editors:
Brian Roark, Ani Nenkova
Venue:
TACL
SIG:
Publisher:
MIT Press
Note:
Pages:
740–755
Language:
URL:
https://aclanthology.org/2021.tacl-1.45
DOI:
10.1162/tacl_a_00395
Bibkey:
Cite (ACL):
Gongbo Tang, Philipp Rönchen, Rico Sennrich, and Joakim Nivre. 2021. Revisiting Negation in Neural Machine Translation. Transactions of the Association for Computational Linguistics, 9:740–755.
Cite (Informal):
Revisiting Negation in Neural Machine Translation (Tang et al., TACL 2021)
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PDF:
https://aclanthology.org/2021.tacl-1.45.pdf
Video:
 https://aclanthology.org/2021.tacl-1.45.mp4