Grammatical error detection from English utterances spoken by Japanese

This paper describes methods to recognize English utterances by Japanese learners as accurately as possible and detects grammatical errors from the transcription of the utterances. This method is a building block for the voice-interactive Computer-Assisted Language Learning (CALL) system that enables a learner to make conversation practice with a computer. A difficult point for development of such a system is that the utterances made by the learners contain grammatical mistakes, which are not assumed to happen in an ordinary speech recognizer. To realize generation of accurate transcription including grammatical mistakes, we employed a language model based on an N-gram trained by generated texts. The text generation is based on grammatical error rules that reflect tendency of grammatical mistakes made by Japanese learners. The experimental results showed that the proposed method improved recognition accuracy compared with the conventional recognition and error detection method.