Teaching the pronunciation of Japanese double-mora phonemes using speech recognition technology
A CALL (computer-aided language learning) system was developed for teaching the pronunciation of Japanese double-mora phonemes to non-native speakers of Japanese. Double-mora vowels and single-mora vowels are spectrally almost identical but their phone durations differ significantly. Similar conditions exist between moraic nasals and non-moraic nasals, and between moraic and non-moraic obstruents. Our CALL system asks the learner to read minimal pairs. Speech recognition technology is used to measure the durations of each phone and the system tells the learner the likelihood of native speakers understanding the learner's utterance as the learner intended. These intelligibility scores are based on perception experiments where native speakers judged the confusability of minimal pairs containing phones with various synthesized durations. The system then instructs the learner to either shorten or lengthen his pronunciation. The learner can terminate training when his communicative performance has met his expectations. For instance, when a learner hits a learning plateau, intelligibility indices can help him decide whether further learning effort is worthwhile. Given that most adult learners can never attain complete nativeness, it is of practical use to be told when non-native accents cannot be removed further. Learning experiments show that learners quickly capture the relevant duration cues.
speech recognition duration pronunciation teaching tokushuhaku