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Articulator Movement Stability Across a Period of Phonemic Development
Maria I. Grigos

Articulator movement stability was compared between adults and 18 month old children as they acquired the voicing contrast for /p/ and /b/. A movement tracking system recorded jaw, lower lip and upper lip displacements as subjects produced the target utterances /papa/ and /baba/. Displacement signals were time and amplitude normalized and the spatiotemporal index (STI) (Smith, Goffman, Zelaznik, Ying & McGillem, 1995) was computed to examine the variability in movement trajectories across repeated productions of target utterances. Results revealed significant decreases in jaw, lower lip and upper lip variability in children as they acquired the voicing contrast. Variability changes in the jaw were more robust than in the lower or upper lip. Overall, a comparison of jaw, lower lip and upper lip movement trajectories across sessions in the children revealed them to most closely resemble adult patterns when the voicing contrast was acquired. These results suggest that the stability of articulator movements increases with phonemic acquisition in children.

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