Dynamics of F0 planning and production: contextual and rate effects on Thai tone gestures
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This dissertation studies the mapping of a phonological representation to phoneticimplementation, and its consequences for theories of coarticulation and speech production, in physical space and real time through the lens of two production experiments on contextual variation in the production of Thai tones. Experiment 1 presents the results of an acoustic investigation where the Thai Falling and Rising tone productions are studied as a function of following tonal context, speech rate, and their interaction. This experiment demonstrates the existence of systematic anticipatory dissimilatory contextual tonal variation effects. Experiment 2 presents the result of an acoustic and electromagnetic articulography (EMA) investigation of consonants, vowels, and tones production in Thai. The effects of following tonal contexts, speech rate, and their interaction are examined. Four main findings emerge. First, we find that tones are more stably anchored to articulatory events rather than acoustic events. Second, all observed timing patterns displayed by Thai speakers are compatible with a split-gesture competitive coupling model of tone. Third, tonal contexts produce effects on inter- and intragestural tonal timing that offer a partial basis for the dissimilatory effects, albeit not a complete one. Fourth, asymmetric effects of rate on consonantal closures, releases, vowels, and tones duration are uncovered. We argue that modeling dissimilatory effects among tones reported in experiment 1 and 2 requires a conceptual dissociation between observed contextual changes in tonal targets and their spatio-temporal execution as gestures. In other words, models of phonology and speech production should comprise both a coproduction and a lookahead coarticulation component. This is computationally implemented by adding an intentional planning field to the Task Dynamic model of Articulatory Phonology. The articulatory timing patterns reported in experiment 2 are modeled using a computational implementation of the coupled oscillator model of Articulatory Phonology. It is shown that such a model can generate both the most commonly observed group patterns and all the patterns of individual variation by minimally altering coupling strength between pairs of gestural planning oscillators. In this way the model can unify an invariant phonological representation with surface phonetic variation. Model limitations and relationships to phonological theory are also discussed. In sum, this dissertation presents empirical and modeling evidence that advances the understanding of coarticulatory patterns and articulatory timing of oral and tonal gestures.
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