Neural Confnet Classification: Fully Neural Network Based Spoken Utterance Classification Using Word Confusion Networks

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This paper describes neural ConfNet classification, a novel fully neural network based spoken utterance classification method that uses word confusion networks (ConfNets). Our motivation is to establish a spoken utterance classification method that can precisely understand natural language and robustly handle automatic speech recognition (ASR) errors. Remarkable progress has been made in neural networks for accurate modeling, however, most previous methods could not handle ASR errors since they were developed for reference transcriptions. Therefore, in our work we utilized ConfNets, which are compact and efficient graph representations of ASR hypotheses. Our idea is to regard the ConfNet as a sequence of bag-of-weighted-arcs and introduce a mechanism that converts the bag-of-weighted-arcs into a continuous representation called a modified weighted sum representation. This enables us to flexibly connect ConfNets to arbitrary model structures developed for reference transcriptions. We demonstrate the effectiveness of the neural ConfNet classification in dialogue act, extended named entity, and question type classification tasks.