Automatic Evaluation and Analysis of Idioms in Neural Machine Translation
Summary
Idiomatic phrases such as "under the weather" have figurative meanings, so NMT systems often render them word by word. Research on this problem has been slowed because there was no automatic way to count such literal mistakes.
The authors introduce LitTER, a metric that needs no hand-made blocklists, unlike Shao et al. (2018). It works in three steps:
- For each annotated source idiom, it builds candidate error lists from bilingual dictionaries (MUSE).
- It drops any list whose words appear in the reference translation.
- It flags a hypothesis if it contains a remaining entry.
LitTER is paired with an alignment-based accuracy measure (APT-Eval), and both are macro-averaged per idiom.
Using en→fr and en→es data from Europarl v7, WMT and IWSLT 2017, the authors extract sentences containing 225 English idioms. They train models under zero-shot, joint and upsampled conditions. Initializing from mBART gives large targeted gains, even when the test idioms never occurred in the parallel training data. Probing shows that randomly initialized models largely ignore the context around an idiom, while pretrained ones respond to it.
The work provides a reusable toolkit for evaluating figurative-language translation.
Key points
- LitTER metric: it reports the share of translations containing dictionary-derived literal renderings of idiom words. Reference filtering removes a word's whole synonym list to avoid false alarms.
- Data: a manually collected, public list of 225 English idioms. Sentences containing them are matched and span-annotated with a pattern-matching tool built on Spacy's rule-based engine. For each idiom, half the sentence pairs go to idiom-train and half to idiom-test.
- Training conditions and metrics:
- Zero: no test idioms in training.
- Joint: idiom-train added to the regular data.
- Upsampling: idiom-train repeated N times.
- Global evaluation uses WMT newstest and IWSLT'17. Targeted evaluation uses LitTER and APT-Eval (unigram precision, ChrF).
- Model variants: random initialization, mBART, and noisy mBART fine-tuning (masking or replacing 10% of source or target tokens).
- Limitations and release: LitTER struggles with compound-rich languages such as German and should be used alongside standard metrics. Code and data are at github.com/amazon-research/idiom-mt.
Cited by
- ID10M-JAM: Stress-Testing Idiom Identification Under Challenging Context
- Crossing the Threshold: Idiomatic Machine Translation through Retrieval Augmentation and Loss Weighting
Cite
@inproceedings{baziotis2023automatic,
title = {{Automatic Evaluation and Analysis of Idioms in Neural Machine Translation}},
author = {Baziotis, Christos and Mathur, Prashant and Hasler, Eva},
booktitle = {Proceedings of the 17th Conference of the European Chapter of the Association for Computational Linguistics},
year = {2023},
doi = {10.18653/v1/2023.eacl-main.267},
url = {https://doi.org/10.18653/v1/2023.eacl-main.267}
}References
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