Optimal Transport for Unsupervised Hallucination Detection in Neural Machine Translation

Nuno M. Guerreiro, Pierre Colombo, Pablo Piantanida, André Martins


Abstract
Neural machine translation (NMT) has become the de-facto standard in real-world machine translation applications. However, NMT models can unpredictably produce severely pathological translations, known as hallucinations, that seriously undermine user trust. It becomes thus crucial to implement effective preventive strategies to guarantee their proper functioning. In this paper, we address the problem of hallucination detection in NMT by following a simple intuition: as hallucinations are detached from the source content, they exhibit encoder-decoder attention patterns that are statistically different from those of good quality translations. We frame this problem with an optimal transport formulation and propose a fully unsupervised, plug-in detector that can be used with any attention-based NMT model. Experimental results show that our detector not only outperforms all previous model-based detectors, but is also competitive with detectors that employ external models trained on millions of samples for related tasks such as quality estimation and cross-lingual sentence similarity.
Anthology ID:
2023.acl-long.770
Volume:
Proceedings of the 61st Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)
Month:
July
Year:
2023
Address:
Toronto, Canada
Editors:
Anna Rogers, Jordan Boyd-Graber, Naoaki Okazaki
Venue:
ACL
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
13766–13784
Language:
URL:
https://aclanthology.org/2023.acl-long.770
DOI:
10.18653/v1/2023.acl-long.770
Bibkey:
Cite (ACL):
Nuno M. Guerreiro, Pierre Colombo, Pablo Piantanida, and André Martins. 2023. Optimal Transport for Unsupervised Hallucination Detection in Neural Machine Translation. In Proceedings of the 61st Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers), pages 13766–13784, Toronto, Canada. Association for Computational Linguistics.
Cite (Informal):
Optimal Transport for Unsupervised Hallucination Detection in Neural Machine Translation (Guerreiro et al., ACL 2023)
Copy Citation:
PDF:
https://aclanthology.org/2023.acl-long.770.pdf
Video:
 https://aclanthology.org/2023.acl-long.770.mp4