Comparison of Native and Non-native Evaluations of the Naturalness of Japanese Words with Prosody Modified through Voice Morphing

Abstract

Information on what kinds of mispronunciation cause the great- est loss in naturalness can be used in guidance to help learn- ers achieve their goals of speaking with good pronunciation. We recorded Japanese words spoken by bilinguals in Tokyo Japanese and in foreign accents (English and Korean) and mor- phed them together with STRAIGHT emphasizing different acoustic parameters. By using STRAIGHT, we can simulate a wide variety of English-accented and Korean-accented pronun- ciations of Japanese. Then, we had native Japanese speakers and non-native speakers (Australian) evaluate the naturalness of these morphed utterances. The experimental results showed that Australian learners were very insensitive to the difference between native and non-native pitch although Japanese speakers were critically sensitive to these errors. Following these results, we give some pedagogical suggestions on what kind of pronun- ciation guidance is necessary for learners to become aware of what is unnatural to native speakers.