The long-range goal of this research is to contribute to an understanding of the motor control of speech production, including its variability, efficiency and communicative effectiveness. We will build on our initial findings of acoustic goals, clarity versus economy of effort, kinetic performance limits and vocal-tract modeling, and on the work of new collaborators. We will refine a theoretical overview with experiments based on the following hypotheses: (1) Segmental control mechanisms for the production of phonemic contrasts are based on acoustical goals. We will examine motor equivalence in reaching those goals. (2) The acoustic goals are determined partly by saturation effects (non-linear quantal relations) between motor commands and articulatory movements and between articulation and sound. We will study saturation effects in a bite block experiment. (3) To achieve the goals, speech movements are planned so that perceptual contrast is achieved with minimal effort. We will examine measures of speech clarity and articulatory effort under varying speech conditions. (4) Programming to achieve acoustic goals must utilize an internal model of the relation between motor commands and acoustic results. We will examine properties of that internal model with a speech sensorimotor adaptation paradigm. (5) The relation between motor commands and acoustic results includes biomechanical constrains, which we study with physiological vocal-tract models. This work will include: (a) further development and use of speaker-specific physiological/biomechanical models of the supra-glottal vocal tract, (b) collection of detailed acoustic, movement, force, EMG, MRI and aerodynamic data from several speakers to provide bases for model development and validation and for quantitative exploration of biomechanical saturation effects, and (c) further development of control models and their use in driving the biomechanical models in tests of hypotheses about acoustic goals, saturation effects, economy of effort and dynamical constraints. (6) The nature of relations between perception and production and their degree of refinement of the internal model may differ across speakers. We measure speakers' acuity in speech discrimination and relate those measures to differences among them in speech kinematics and acoustics. In these studies we will record and analyze the acoustic signals and movements of points on the mandible, lips and tongue using our EMMA movement transducer system; we also gather anatomical data with MRI and we make measurements of EMG, contact pressures, air pressure and air flow. We also conduct several kinds of perceptual experiments and compare the results with those from the production experiments.
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