This paper investigates whether articulatory strategies for vowel length production mature synchronously with phonemic competence in Japanese speakers. Japanese is a mora-timed language that phonemically distinguishes short and long consonants (e.g., kama “sickle” versus kamma “comma") and vowels (e.g., kado “angle” versus kaado “card") lexically. Previous research demonstrates that mora rhythm is established by age 5, with children capable of producing and perceiving these distinctions. We previously conducted physiological research on Japanese mora using EMA and lip movement video analysis, finding enhanced articulatory movements for long vowels in adults but inconsistent patterns in children. The present study examined tongue shape dynamics using ultrasound imaging, comparing vowel length production in 20 adults and 30 children aged 6–12 years. Participants produced word pairs contrasting short and long vowels across all five Japanese vowels (/i,e,a,o,u/ vs. /ii,ee,aa,oo,uu/). Preliminary results revealed systematic articulatory differences in adults, with long vowels showing vertical tongue displacement: lowering for open vowels, raising for close vowels, consistent with previous findings. However, child speakers exhibited inconsistent tongue shape differences between short and long vowels. These findings indicate that phonemic operations develop before physiological operations during acquisition. The age-related differences provide valuable data for developing physiological models of speech timing acquisition.
Shirose et al. (Wed,) studied this question.