Retention of devoiced vowels in Tokyo Japanese: Evidence from lip articulation

In Tokyo Japanese, high vowels /i/ and /u/ are frequently devoiced when they are surrounded by voiceless obstruents. Controversy remains over whether vowel gestures in devoiced vowels are retained or instead deleted. Both static (Iwasaki et al., 2020) and dynamic (Iwasaki et al., 2022) ultrasound data have indicated that vowel-specific lingual gestures can persist even when vowels are devoiced. This study focuses on the lip articulation of devoiced vowels by examining lateral lip aperture, where lower values index a greater degree of the rounding of vowels. Native speakers of Tokyo Japanese produced nonce word pairs with the form of /C1VC2V2toko/. V1 was either /i/ or /u/. C1 and C2 were either voiced or voiceless, which determined the voicing of V1. Lateral lip aperture during the first mora was calculated by identifying facial landmarks using OpenFace 2.0 (Baltrusaitis et al., 2018), and compared across vowel quality (/i/ vs./u/) and vowel voicing (devoiced vs. voiced). Preliminary results show that lateral lip aperture is larger for /i/ than for /u/ in both devoiced and voiced environments, indicating that these vowels maintain their labial specifications even when devoiced, providing additional evidence that devoiced vowels can retain their articulatory gestures.