Automatic extraction of diverse expressions from learner corpus and its application to the paraphrasing strategy teaching

Language learners use various kinds of communication strategies to compensate their imperfect knowledge on the target language, especially vocabulary.Paraphrase is one of the important strategies.It must be worth doing to teach how paraphrase in foreign language communication can be done more effectively.In vocabulary teaching, if the certain word entry is introduced with several other relevant words or expressions, it would be quite helpful for learners to do more successful paraphrase.In this research, we have done the experiment to see how this kind of expanded teaching of vocabulary or expressions can be accomplished by using diverse expressions extracted from the spoken corpus of Japanese learner English, “The NICT JLE (Japanese Learner English) Corpus”.In the experiment, we first made the keyword list based on the small amount of English native speakers' utterances by hand. Then, we automatically extracted the diverse expressions which describe the particular matter from the learner data to make the learners' expression list.We have obtained approximately 50% for recall and precision for a complex task, while for an easy task, 70% and 60% for recall and precision respectively.It is assumed that this expression list can be utilized for teaching paraphrasing strategy as one of the examples of the use of learner corpora in the foreign language classroom.