On the two rhotic schwas in Southwestern Mandarin: when homophony meets morphology in articulation.

This is an acoustic and articulatory study of the two rhotic schwas in Southwestern Mandarin (SWM), i.e., the er-suffix (a functional morpheme) and the rhotic schwa phoneme. Electromagnetic Articulography (EMA) and ultrasound results from 10 speakers show that the two rhotic schwas were both produced exclusively with the bunching of the tongue body. No retroflex versions of the two rhotic schwas were found, nor was retraction of the tongue root into the pharynx observed. On the other hand, the er-suffix and the rhotic schwa, though homophonous, significantly differ in certain types of acoustic and articulatory measurements. In particular, more pronounced lip protrusion is involved in the production of the rhotic schwa phoneme than in the er-suffix. It is equally remarkable that contrast preservation is not an issue because the two rhotic schwas are in complementary distribution. Taken together, the present results suggest that while morphologically-induced phonetic variation can be observed in articulation, gestural economy may act to constrain articulatory variability, resulting in the absence of retroflex tongue variants in the two rhotic schwas, the only two remaining r-colored sounds in SWM.