Voice onset time and <i>F</i> perturbation under conditions of mixed airstream mechanism

Pulmonic and velaric airstream mechanisms are employed together in the production of clicks and accompanying vowels. Questions thus emerge as to the temporal and microprosodic coordination of these two mechanisms, particularly with respect to the phonatory characteristics of clicks. This report is on the acoustic measurement of the post-alveolar click in Sesotho, with particular reference to VOT and F0 perturbations. There are two phonemically distinct varieties of click in Sesotho, which might be characterized as aspirated and unaspirated in accordance with orthographic conventions. The unaspirated click has a mean VOT of approximately 40 ms on the order of voiceless aspirated plosives in English. The aspirated click has a mean VOT of approximately 120 ms, greater than any plosive type reported by Lisker and Abramson [Language 47, 767–785 (1971)]. The F0 values were measured pre- and post-click in both word-initial and word-medial clicks. Our data indicate a consistent fall in F0 immediately prior to a click, regardless of lexical tone, presence of word boundary, and the distinctive prosody of interrogatives. This perturbation of fundamental frequency may be indicative of an intrinsic property of click production. By contrast, measures of post-click F0 reveal a less regular pattern of microchange both across the silent interval and during the initial glottal cycles at post-click vowel onset; these phenomena are apparently influenced by lexical tone.