The overall aim of our research is to establish whether speech production goals for fricatives are articulatory, aerodynamic, aeroacoustic, or acoustic. The results of this work are also expected to have implications for the general theory of the goals of speech production, since fricative properties are a superset of the properties of other segments. In the initial experiments we explore whether goals for fricatives are aerodynamic by examining initiation and maintenance of turbulence, and interactions of the voicing and noise sources. The next set of experiments explores whether the goals for fricatives are aeroacoustic by examining cases in which the aeroacoustic source changes significantly as a result of minor articulatory changes. The following set of experiments explores acoustic goals by examining differences in control of the acoustic vocal-tract filter in voiced and voiceless fricatives. We distinguish between aeroacoustic and acoustic goals based on whether the goal concerns the properties of the sound source (aeroacoustic) or the filter (acoustic). If fricatives prove to have none of these goals, we will conclude that the goals are articulatory only, and will examine possible articulatory tradeoffs. Finally, we explore the ways in which goals for contiguous fricatives interact in fricative clusters. For all of these experiments we use three main experimental domains: mechanical models of the vocal tract in which articulatory and aerodynamic variables can be precisely controlled, computer simulations of acoustic, aerodynamic and aeroacoustic phenomena in the vocal tract with which similarity classes can be explored, and articulatory, aerodynamic and acoustic measurements of human subjects, which will serve to validate the models and simulations. We expect our research to contribute usefully to the debate about speech production, to advance our understanding of disfluencies involving fricative pronunciation, to broaden the range of analysis and simulation tools used for fricatives by the speech community, and to extend basic research on fricative production.
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