Attention-based Multimodal Neural Machine Translation
Summary
This paper, a system for the WMT 2016 multimodal translation shared task, asks whether images can help an attention-based NMT model translate English image captions into German, for instance by disambiguating words. The authors treat visual features as extra encoder steps, so the decoder can attend to image and text jointly. Images are represented by fc7 activations (4096 dimensions) from VGG-19, which a learned matrix maps into the text embedding space. Three encoders are compared:
- Model 1 adds a single global image vector to the word sequence.
- Model 2 prepends up to four object regions found by the R-CNN region proposal network, ordered from smallest to largest, plus the whole image.
- Model 3 runs parallel LSTM threads with shared weights. Each thread starts from one visual feature and then reads the sentence, and the thread outputs are merged by average pooling.
The parallel model worked best. It beat the text-only baseline and was comparable to the strongest Moses-based entries in the challenge. Re-ranking candidates with a bilingual dictionary raised METEOR further. The work is an early demonstration that attending over image regions can aid translation.
Key points
- Visual input consists of VGG-19 fc7 vectors for the whole image and for the top 4 regions proposed by the Faster R-CNN RPN, with zero-padding when fewer objects are detected. Ordering regions by ascending size beat descending, random and categorical orders.
- Model 3 (4 regional threads plus 1 global thread) reached 36.5 BLEU and 54.1 METEOR. This is +2.0 BLEU and +2.3 METEOR over the text-only model.
- Three re-scoring methods were tested on Model 3 candidates:
- A single-layer LSTM language model (300 hidden units) trained on MSCOCO and IAPR TC-12 captions (56,968 sentences) gave almost no gain.
- A bilingual autoencoder (256-200-128 layers) lowered both metrics, likely because of overfitting on scarce bilingual data.
- Bilingual dictionary matching raised METEOR to 55.2 (+1.1), while BLEU dropped to 35.7.
- The authors suggest adding further modalities, such as audio, as future work.
Cited by
- Massively Multilingual Neural Machine Translation in the Wild: Findings and Challenges
- Evaluating Discourse Phenomena in Neural Machine Translation
- 文档级神经机器翻译综述
- A Shared Task on Multimodal Machine Translation and Crosslingual Image Description
Cite
@inproceedings{huang2016attention,
title = {{Attention-based Multimodal Neural Machine Translation}},
author = {Huang, Po-Yao and Liu, Frederick and Shiang, Sz-Rung and Oh, Jean and Dyer, Chris},
booktitle = {Proceedings of the First Conference on Machine Translation: Volume 2, Shared Task Papers},
year = {2016},
doi = {10.18653/v1/w16-2360},
url = {https://doi.org/10.18653/v1/w16-2360}
}References
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