Generational differences in the low tones of Black Lahu

We investigate apparent-time variation of the low falling (T21) and low level (T11) tones of the Black Lahu language of Yunnan, China. Linear mixed-effects modeling of spontaneous speech shows that both tones have a higher F0 trajectory among younger speakers and in certain phonetic environments. Since F0 is known to lower with increasing age, for comparison we also analyze variation in the high rising tone (T45) and find no evidence of generational difference. This suggests that the effect of age on low tones is not due to physiological change across the life span. We leave open the question of whether this result reflects a change in progress or a stable sociotonetic difference between older and younger speakers. This study contributes towards two underrepresented areas of sound change research: (1) sociotonetic approaches to tone variation in naturalistic speech styles, and (2) engagement with Indigenous scholars who are cultural insiders in small rural minority language communities.