| Summary: | Coarticulation is an important source of new phonological contrasts. When speakers interpret effects such as nasalization, glottalization, and rhoticization as an inherent property of a vowel, a new phonological contrast is born. Studying this process directly is challenging because most vowel systems are stable and phonological change likely follows a long transitional period in which coarticulation is conventionalized beyond its mechanical basis. We examine the development of a new vowel feature by focusing on the emergence of rhotic vowels in Kalasha, an endangered Dardic (Indo-Aryan) language, using biomechanical and acoustic modeling to provide a baseline of pure rhotic coarticulation. Several features of the Kalasha rhotic vowel system are not predicted from combining muscle activation for non-rhotic vowels and bunched and retroflex approximants, including that rhotic back vowels are produced with tongue body fronting (shifting the backness contrast to principally a rounding contrast). We find that synthesized vowels that are about 30% plain vowel and 70% rhotic are optimal (i.e., they best approximate observed rhotic vowels and also balance the acoustic separation among rhotic vowels with the separation from their non-rhotic counterparts). Otherwise, dispersion is not generally observed, but the vowel that is most vulnerable to merger differs most from what would be expected from coarticulation alone.
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