Production of single and geminate stops in Japanese three- and four-mora words

This study examined the durational structure of single and geminate stop distinction produced in three- and four-mora words of Japanese, (C1)V1(C2)C2V2X [(C2)C2 = the contrasting consonants; X = a CV mora, the moraic nasal, or a long vowel as part of V2]. The questions addressed were how factors such as speaking rate, segmental variability, and moraic composition of words affected the stop quantity distinction in words longer than well-studied disyllabic words, and whether there exists an invariant parameter that classified these two stop categories. Results showed that all of those factors systematically affected the duration of the contrasting stop closure, the unit of [(C1)V1(C2)C2V2], and the entire three- and four-mora words. However, the durational units of moras and words were well-structured, and the ratio of the contrasting stop closure to the [(C1)V1(C2)C2V2] unit, as well as the ratio of the closure to the entire word, were found to be invariant in indicating the stop quantity distinction. These results support the theory of relational acoustic invariance [Pickett et al., Phonetica 56, 135–157 (1999)] on the part of production. Furthermore, the results provide insight into different versions of Japanese mora hypothesis [Han, The Study of Sounds 10, 65–80 (1962); Port et al., J. Acoust. Soc. Am. 81(5), 1574–1585 (1987)], which have been under debate for five decades.