Tai Khamti stop phonation contrasts: Historical origins and phonetic documentation

Whereas most Tai languages contrast three series of oral stops, Tai Khamti, an endangered Southwestern Tai language of Myanmar and India, is described as having just two: plain voiceless and voiceless aspirated. To the best of our knowledge, we present here the first acoustic phonetic analysis of this contrast, examining voice onset time (VOT) in 245 tokens from fieldwork recordings of two native speakers. The results reveal a robust plain/aspirated contrast with a mean VOT difference of 47.5 ms and a very large effect size (Cohen’s d = 3.03). We also trace the historical origins of this two-way contrast through comparison with the onset inventory of Proto-Tai: the plain voiceless series reflects a merger of Proto-Tai voiced and voiceless stops, the voiceless aspirated series has a dual origin in Proto-Tai fricatives and certain onset clusters, and Proto-Tai voiced implosive stops have lenited to nasal stops. We further show that Proto-Tai voicing contrasts are continued in Tai Khamti via tonal innovations. The synchronic acoustic and historical phonological analyses presented here document a previously underdescribed contrast, laying a foundation for future investigation into tonogenesis in Tai Khamti and in the Tai languages more broadly, where innovations affecting both onset laryngeal contrasts and existing tonal contrasts must be traced.