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End-to-end speech-to-dialog-act recognition

Paper · 2020 · Viet-Trung Dang, Tianyu Zhao, Sei Ueno et al.

Summary

Recognizing dialog acts (DAs) from speech usually works as a pipeline. An ASR system writes a transcript, and a separate classifier, trained on clean human transcripts, labels it. Recognition mistakes then spread downstream, and acoustic cues such as pauses are discarded. The authors replace this chain with a single network. An attention-based acoustic-to-word ASR model hands its decoder output vector from just before the softmax layer (the "ASR feature") to an LSTM-based DA classifier. The classifier encodes words and then a history of utterances. They train this coupling step by step and then fine-tune it end to end with a weighted multi-task loss. A hybrid variant adds ordinary word embeddings of the hypothesis to the ASR feature. A final extension adds a DA-boundary token to the ASR vocabulary, so the recognizer segments utterances while transcribing. Experiments on Switchboard with SwDA tags show that the unified approach beats the pipeline. With n-best beam search, DA accuracy rises by 2.41 points absolute. This makes a case for passing soft internal representations between stages instead of committed outputs.

Key points

  • Data: Switchboard audio aligned with the Switchboard Dialog Act corpus (SwDA, built on Penn Treebank 3 annotations). It has 1,126 conversations, 213.5k utterances, a 27.2k-word vocabulary and 43 DA tags. Of these, 20 conversations are held out for test and 40 for validation.
  • Pipeline baseline: the classifier reaches an error rate of 26.79% (history 1) and 25.06% (history 5) on reference transcripts. On ASR output with 27.76% WER, the error rate degrades to 31.85% and 31.10%.
  • Retraining the classifier on ASR transcripts did not reliably help. Feeding the ASR feature did, and beam search and n-best hypotheses helped more in that setting.
  • End-to-end fine-tuning gave the best 1-best results, which were statistically significant. Its benefit disappeared with beam search, because the joint loss only sees the 1-best hypothesis. The hybrid input added a small further gain.
  • Segmentation is folded into recognition by appending an utterance-end symbol after every DA in the training targets. The DA tag is then predicted at each such symbol.

Interesting ideas

  • I1. Hand the downstream module the upstream model's pre-softmax vector rather than its chosen symbol, so a wrong pick still carries a representation near the right one.
  • I2. Make boundary detection part of the vocabulary by emitting a special end-of-unit token, so segmenting and labelling happen in one pass using the same evidence.
  • I3. Sum the embedding of the committed hypothesis with the soft feature, because the discrete form is sharper when upstream is right and the soft form is safer when it is wrong.
  • I4. When fine-tuning jointly, keep the downstream loss weight small so the upstream model's accuracy is not sacrificed for the downstream task.
  • I5. Compare three training regimes for the downstream model: gold input, noisy upstream output, and upstream latent features. In this paper, naive training on noisy output was not enough.

For Mova

How these ideas could serve Mova, our small open language model — its files, stages and tests:

  • I1 (tree): the parser could read the tagger's internal tag/lemma vectors alongside its decided tag, while still logging the discrete decision for explainability.
  • I2 (tokens): sentence and clause splitting in crate en could be emitted as a boundary token by the tagger instead of running as a separate rule pass.
  • I3 (frames): speech-act classification in prag could combine the chosen UD tree with the parser's uncertainty signal, falling back on the soft signal where the arcs are shaky.
  • I4 (learn): when gparse is tuned with a frame-level objective, a low weight on the frame loss would protect LAS; parsing scores should be checked before and after.
  • I5 (learn): evaluate frame and answer modules on gold trees, silver/witness-parser trees and soft parser features, to see where robustness actually comes from.

Our summary of the paper, in our own words — not its text. The work belongs to its authors; read it at the links above.

 Institutions

Cite

Cite as Viet-Trung Dang, Tianyu Zhao, Sei Ueno, Hirofumi Inaguma and Tatsuya Kawahara. 2020. End-to-end speech-to-dialog-act recognition. arXiv:2004.11419.

The paper itself, not this page. BibTeX from the library's record of the work. DOI 10.48550/arxiv.2004.11419 · arXiv 2004.11419

@misc{dang2020end,
  title = {{End-to-end speech-to-dialog-act recognition}},
  author = {Viet-Trung Dang, Tianyu Zhao, Sei Ueno, Hirofumi Inaguma and Tatsuya Kawahara},
  year = {2020},
  doi = {10.48550/arxiv.2004.11419},
  eprint = {2004.11419},
  archivePrefix = {arXiv},
  url = {https://doi.org/10.48550/arxiv.2004.11419}
}

References

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