Gradient realization of Mandarin nasal codas

Abstract

Impressionistic studies suggested that Mandarin nasal codas optionally delete before vowels (/dan/ + /ai/->[dã.ai]) and assimilate to the following stops in place (/dan/ + /pai/->[dam.pai]). In this EMA study, we found that both processes are not phonological changes but are gradient processes modulated by speech rates. Three native Mandarin speakers read disyllabic words with n/ŋ codas before /a/ and /p/ in a carrier sentence at three speech rates. The tongue tip trajectories show that both nasals retain a reduced tongue gesture before /a/. The reduction INCREASEs as speed INCREASEs and is more variant in faster speech. The lower lip trajectories show that the labial gesture of /p/ occurs earlier when preceded by nasal codas. The time-normalized duration of this gestural advance DECREASEs as speed INCREASEs (and decreases at a slower rate in slower speech), suggesting less gestural overlap at faster speed. Such a relationship is opposite to the reduction-speed relationship. The articulatory evidence shows that although not perceptual salient, there is a reduced tongue gesture for nasals before vowels and gestural overlap between stops and preceding nasals. The non-linear effects of speed on gestural reduction and overlap suggest both are gradient phonetic processes; yet, their opposite relationships to speed suggest different implementation mechanisms.