Speech Prosody 2004
Japanese is crucially different from other accent languages in having a number of unaccented words, or words that are pronounced with a rather flat F0 contour. This paper illuminates some phonological factors responsible for the emergence of this peculiar type of word accent in Tokyo Japanese. It demonstrates, specifically, that unaccentedness emerges in words of some specific syllable structures - in four-mora loanwords that consist of four light (monomoraic) syllables as well as in three-mora words consisting of a light syllable followed by a heavy (bimoraic) syllable.
Bibliographic reference. Kubozono, Haruo / Ogawa, Shinji (2004): "Emergence of unaccented words in Japanese", In SP-2004, 33-36.