Can Transformer be Too Compositional? Analysing Idiom Processing in Neural Machine Translation

Verna Dankers, Christopher Lucas, Ivan Titov


Abstract
Unlike literal expressions, idioms’ meanings do not directly follow from their parts, posing a challenge for neural machine translation (NMT). NMT models are often unable to translate idioms accurately and over-generate compositional, literal translations. In this work, we investigate whether the non-compositionality of idioms is reflected in the mechanics of the dominant NMT model, Transformer, by analysing the hidden states and attention patterns for models with English as source language and one of seven European languages as target language.When Transformer emits a non-literal translation - i.e. identifies the expression as idiomatic - the encoder processes idioms more strongly as single lexical units compared to literal expressions. This manifests in idioms’ parts being grouped through attention and in reduced interaction between idioms and their context.In the decoder’s cross-attention, figurative inputs result in reduced attention on source-side tokens. These results suggest that Transformer’s tendency to process idioms as compositional expressions contributes to literal translations of idioms.
Anthology ID:
2022.acl-long.252
Volume:
Proceedings of the 60th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)
Month:
May
Year:
2022
Address:
Dublin, Ireland
Venue:
ACL
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
3608–3626
Language:
URL:
https://aclanthology.org/2022.acl-long.252
DOI:
10.18653/v1/2022.acl-long.252
Bibkey:
Cite (ACL):
Verna Dankers, Christopher Lucas, and Ivan Titov. 2022. Can Transformer be Too Compositional? Analysing Idiom Processing in Neural Machine Translation. In Proceedings of the 60th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers), pages 3608–3626, Dublin, Ireland. Association for Computational Linguistics.
Cite (Informal):
Can Transformer be Too Compositional? Analysing Idiom Processing in Neural Machine Translation (Dankers et al., ACL 2022)
Copy Citation:
PDF:
https://preview.aclanthology.org/emnlp-22-attachments/2022.acl-long.252.pdf
Software:
 2022.acl-long.252.software.zip
Video:
 https://preview.aclanthology.org/emnlp-22-attachments/2022.acl-long.252.mp4
Code
 vernadankers/mt_idioms