Utterance verification using garbage words for a hospital appointment system with speech interface

On a system that captures spoken dialog, users often use out-of-domain utterances to the system. The speech recognition component in the dialog system cannot correctly recognize such utterances, which causes fatal errors. This paper proposes a method to verify whether utterances are in-domain or out-of-domain. The proposed method trains systems with two language models: one that can accept both in-domain and out-of-domain utterances and the other that can accept only in-domain utterances. These models are installed into two speech recognition systems. A comparison of the recognizers' outputs provides a good verification of utterances. We installed our method in a hospital appointment system and evaluated it. The experimental results showed that the proposed method worked well.