Experimental and computational investigations of F0 control
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This dissertation examines speakers’ cognitive control of F0, by proposing and evaluating target-control and register-control hypotheses. In the target-control hypothesis, it is individual pitch targets that speakers control to produce variations in F0, whereas in the register-control hypothesis, it is the control of pitch register (in which the pitch targets are defined) that induces F0 variations. These alternative hypotheses are assessed through a production experiment and computational modeling.The production experiment investigates speakers’ (i) pre-planned and (ii) adaptive F0 control. In particular, the experiment examines whether speakers vary F0 parameters (i) according to the initially planned sentence length and (ii) in response to unanticipated changes in the length. For this purpose, a novel experimental paradigm was developed in which the stimuli cueing the parts of the utterance were delayed until after participants initiated an utterance; in this case, participants had to dynamically adapt to the changes in the length and content of the utterance. Analyses of F0 trajectories found strong evidence for both pre-planned and adaptive control. Further analyses were conducted to identify which specific F0 parameter was controlled (targets vs. register), and the results demonstrated the control of pitch register. In the modeling study, a gestural model of F0 control was proposed and evaluated with the experimental data. The main feature of this dynamical model is that the normalized targets of F0 gestures (and F0 tract variable) are mapped to actual F0 values through pitch register parameters. The model parameters were optimized to minimize the difference between the empirical F0 contour and the model-generated contour. Several variants of F0 models were compared to examine the target vs. register-control hypotheses. The results found that the F0 model in which the register parameters varied (with invariant targets) outperformed the model in which the target parameters varied (with constant register), providing further support for the register-control hypothesis. Overall, this dissertation provides evidence that for a given utterance, speakers have a set of invariant cognitive representation of high and low pitch targets, and they control pitch register to realize the abstract representation into different F0 peaks and valleys.
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