Third International Conference on Spoken Language Processing (ICSLP 94)
The intensity measurements of vowels in devoicing environments suggest that high vowel devoicing in Japanese is a natural vowel reduction process resulting from glottal gestural overlap. Earlier work showed that high vowel devoicing appears almost compulsory at the normal speaking rate so long as there is no devoiceable vowel in an adjacent mora. High vowels can sometimes remain voiced in devoicing environments, but their intensity is smaller than that of ordinary vowels. However, in the consecutive devoicing environments, voiced vowels in devoicing environments are not weakened. Two different mechanisms seem to control vowel devoicing depending on the environments.
Bibliographic reference. Kondo, Mariko (1994): "Mechanisms of vowel devoicing in Japanese", In ICSLP-1994, 61-64.