Speech planning influences the acoustic realization of phonological alternation: Evidence from morpho-syntactically complex Mandarin Tone 3 sandhi

Production planning has been shown to affect the application rate of variable phonological alternation. This study investigates how planning could influence the acoustic realization of alternation. We ask whether the acoustic gradience in morpho-syntactically complex Mandarin T3 sandhi is a consequence of speech planning regulating how much information of the T3 allomorph can cascade to downstream acoustics. Building on the production planning hypothesis and cascadedness of speech production, we propose that the availability of T3-sandhi context constrains the cascading process of the T3 allomorph, yielding differences in the amount of T3 residual in the acoustic output. Specifically, a stronger syntactic boundary reduces the likelihood that phonological information embedded in the upcoming word is available during target word production. Consequently, more T3 allomorphic information cascades from the lexical–phonological level to the phonetic level, resulting in more T3-like acoustic output characterized by a shallower rise in f0. Results from 15 speakers’ data showed that, under stronger boundary conditions, T3 sandhi items exhibited a significantly shallower rising slope compared to weaker boundary conditions, while T2 non-sandhi items did not show this effect. This Tone-by-Boundary interaction supported our hypothesis that the acoustic difference stemmed from production planning and cascadedness, not phonetic effects of duration.