Spatiotemporal tongue kinematics from ultrasound imaging: Articulatory divergence in Mandarin apical vowels.

Mandarin apical vowels [ɹ'] and [ɻ'] have resisted articulatory classification: are they vocalized prolongations of the preceding sibilant or independent vowel targets? Using ultrasound imaging and generalized additive mixed models with simultaneous confidence intervals, the tongue contour over space and time in two comparisons has been modeled: each vowel against its sibilant onset and the three vocalic realizations against one another. [ɻ'] continues the /ʂ/ posture while [ɹ'] diverges from /s/, and the three realizations differ from one another, the two apical vowels from [i] and from each other. The Mandarin "apical vowel" label may subsume more than one articulatory strategy.