Empirical Analysis of Beam Search Curse and Search Errors with Model Errors in Neural Machine Translation

Jianfei He, Shichao Sun, Xiaohua Jia, Wenjie Li


Abstract
Beam search is the most popular decoding method for Neural Machine Translation (NMT) and is still a strong baseline compared with the newly proposed sampling-based methods. To better understand beam search, we investigate its two well-recognized issues, beam search curse and search errors, at the sentence level. We find that only less than 30% of sentences in the test set experience these issues. Meanwhile, there is a related phenomenon. For the majority of sentences, their gold references have lower probabilities than the predictions from beam search. We also test with different levels of model errors including a special test using training samples and models without regularization. We find that these phenomena still exist even for a model with an accuracy of 95% although they are mitigated. These findings show that it is not promising to improve beam search by seeking higher probabilities in searching and further reducing its search errors. The relationship between the quality and the probability of predictions at the sentence level in our results provides useful information to find new ways to improve NMT.
Anthology ID:
2023.eamt-1.10
Volume:
Proceedings of the 24th Annual Conference of the European Association for Machine Translation
Month:
June
Year:
2023
Address:
Tampere, Finland
Editors:
Mary Nurminen, Judith Brenner, Maarit Koponen, Sirkku Latomaa, Mikhail Mikhailov, Frederike Schierl, Tharindu Ranasinghe, Eva Vanmassenhove, Sergi Alvarez Vidal, Nora Aranberri, Mara Nunziatini, Carla Parra Escartín, Mikel Forcada, Maja Popovic, Carolina Scarton, Helena Moniz
Venue:
EAMT
SIG:
Publisher:
European Association for Machine Translation
Note:
Pages:
91–101
Language:
URL:
https://aclanthology.org/2023.eamt-1.10
DOI:
Bibkey:
Cite (ACL):
Jianfei He, Shichao Sun, Xiaohua Jia, and Wenjie Li. 2023. Empirical Analysis of Beam Search Curse and Search Errors with Model Errors in Neural Machine Translation. In Proceedings of the 24th Annual Conference of the European Association for Machine Translation, pages 91–101, Tampere, Finland. European Association for Machine Translation.
Cite (Informal):
Empirical Analysis of Beam Search Curse and Search Errors with Model Errors in Neural Machine Translation (He et al., EAMT 2023)
Copy Citation:
PDF:
https://aclanthology.org/2023.eamt-1.10.pdf