Tense and Lax Vowels in the Lahu Dialect of Yunshan: A Laboratory Phonological Study

A controversy exists regarding whether there are tense-lax vowels in Lahu and whether tense-lax phonation should be accorded phonological status, an issue that is closely related to the physiological movement of the larynx. This study presents an experimental analysis of the acoustic features of the Lahu dialect of Yunshan, using electroglottography to collect acoustic and physiological data and employing VoiceSauce and Eggworks to extract glottal features to explore laryngeal mode of motion. The study demonstrates a distinct tense-lax phonation contrast in Yunshan Lahu, which is characterized by multiple types of phonation, differences between front and back parts of tense vowels, and equal importance of tense-lax contrast and vowel length. To contribute to a systematic description of Tibeto-Burman language, this paper proposes to treat tense-lax contrast as the main feature in phonological induction, using length as its accompanying feature for explanation. From the perspective of the path of historical evolution, tenseness comes from the loss of plosive codas, and is also closely related to voiced, aspirated initials. In the process of transforming tense-lax features to tones, tense vowels retained their features of tenseness as a result of falling tones.