• Back
• Next

日本語

In the Japanese language, the consonant /s/ followed by vowel /i/ is pronounced [ɕi], distinct from /s/ followed by other vowels [sa], [sɯ], [se], and [so], because of the palatalized tongue articulation. Similarly, /h/ followed by /i/ is pronounced [çi], distinct from /h/ followed by the other vowels [ha], [ɸɯ], [he], and [ho]. In both cases, the articulation is palatalized and often confused. For example, the initial syllables of Japanese words /higasi/ “east” and /hige/ “mustache” are often pronounced /sigasi/ and /sige/, respectively, in Tokyo and a wide area of the Tohoku region of Japan. In addition, the initial syllable of /sichigatsu/ “July” is variably pronounced as /hichigatsu/ throughout Japan. This phenomenon has already been known by researchers in linguistics. However, it was still unclear how the acoustic contrast between the two sounds /hi/ and /si/ was reflected from their articulation.

In this study, the research team observed the tongue movement during the articulation of a Japanese sentence “korega hisi gata” (“This is a rhomboid shape.”) by 10 Japanese subjects using real-time MRI, and found that 3 subjects pronounced /hi/ and /si/ with almost identical places of articulation, while the acoustic contrast between /hi/ and /si/ was audible.

To examine how the acoustic contrast was formed with an apparently identical place of articulation, the research team conducted numerical flow simulations on oral models using a supercomputer. The results demonstrated that the acoustic contrast between /hi/ and /si/ can be produced by the difference in tongue shape in the transverse direction without changing the place of articulation.

In the classification of the International Phonetic Alphabet (IPA), the place of articulation is mainly defined by the position of the narrowing of the oral passage in the anterior-posterior direction. However, the current findings show the possibility of changing the sounds of /hi/ and /si/ with different tongue shapes in the transverse direction, suggesting the necessity of including a new parameter for the IPA.

"The pronunciations of /hi/ and /si/ are often used in Japanese and articulated unintentionally in a daily conversation,” says the lead author Tsukasa Yoshinaga, assistant professor at Toyohashi University of Technology. “However, to simulate the production of these sounds in our mouths, we need to precisely calculate the generation of many small vortices in turbulent airflow and the sound propagation from these vortices. To simulate them, approximately 80 million computational grid points were set, and the formulas were solved on the grids using a supercomputer. We were excited when we found small vortices causing the acoustic contrast between /hi/ and /si/ in the simulation results."

For future research, the research team believes that understanding the cause of the acoustic contrast between /hi/ and /si/ will provide useful information for obtaining fluency in Japanese articulation. In addition, this knowledge can be useful for the rehabilitation of articulation disorders with speech therapists. Currently, coauthor Kikuo Maekawa, professor at NINJAL, is developing a database of articulatory movies of real-time MRI. Additional analysis for the other syllables will provide us useful information for speech therapists as well as learners of Japanese as a second language.

This work was supported by MEXT as "Program for Promoting Research on the Supercomputer Fugaku" (hp200123, hp200134), JSPS KAKENHI (Grant numbers: JP17H02339, JP19H03976, JP19K21641, JP20H01265, and JP20K14648), and the research budget of the Center for Corpus Development, National Institute for Japanese Language and Linguistics.