This proposal is aimed at understanding the formation of articulatory patterns during speech production, using a strictly operational approach in which theoretical tools and experimental data are developed together. The empirical approach is guided by synergetics, the theory of spontaneous structure formation in open, nonequilibrium systems (Haken, 1975). In synergetics, behavioral patterns produced by multidegree of freedom systems can be characterized by (low-dimensional) collective variables, the so-called order parameters.
We aim to discover these order parameters and their dynamics in the speech production system by studying the stability and loss of stability of spatiotemporal speech patterns using experimental paradigms that allow monitoring of trajectories of multiple articulators. Order parameters have two characteristics to be investigated here. First, they should remain stable or exhibit only weak dependence on """"""""control parameters"""""""" that potentially deform the system. Second, they should exhibit loss of stability at bifurcation points, where the behavior of the system changes abruptly. Based on preliminary work, Section I of the present proposal tests the hypothesis that the continuous relative phasing among observed articulatory components is an essential macroscopic variable that remains stable across transformations in style of speaking, stress, rate, and loudness. Continuous relative phase is a measure derived from individual articulator motions (e.g., tongue, jaws, lips, glottis) and vocal tract variables (e.g., lip aperture, tongue construction). Test of convergence on this candidate order parameter are carried out in Section II, which examine the mechanisms underlying voluntary and involuntary switching among collective states. In addition to their theoretical importance, the experiments proposed are intended to answer the question of where, when and how the speech motor system changes its parameters in simple utterances. In short, a program of research is proposed that seeks to identify the lawful regularities in speech motor patterns that arise in a self- organized fashion, and that structure sound for a listener. Such a characterization of normal speech production is a necessary precursor to the definition and categorization of disordered stated (so-called articulation disorders).
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