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  • Title: Changes in articulator movement variability during phonemic development: a longitudinal study.
    Author: Grigos MI.
    Journal: J Speech Lang Hear Res; 2009 Feb; 52(1):164-77. PubMed ID: 18664683.
    Abstract:
    PURPOSE: The present study explored articulator movement variability during voicing contrast acquisition. The purpose was to examine whether oral articulator movement trajectories associated with the production of voiced/voiceless bilabial phonemes in children became less variable over time. METHOD: Jaw, lower lip, and upper lip movements were recorded longitudinally in six, 19 month-old children as they began producing the voiceless phoneme /p/. Displacement signals were time and amplitude normalized. The spatiotemporal index (A. Smith, L. Goffman, H. Zelaznik, S. Ying, & C. McGillem, 1995) was computed to examine the variability in movement trajectories across repeated productions of target utterances. RESULTS: Spatiotemporal variability of lip and jaw movements significantly decreased as children began producing the voiceless phoneme /p/. A significant negative correlation between the STI and the length of voice onset time (VOT) was also found in the voiceless productions in 4 of the 6 participants. CONCLUSIONS: Oral articulator movement variability is reduced in children across the stabilization of voicing contrast acquisition. Further, the relationship between VOT contrast production and movement variability suggests that a coordinate system between the oral and laryngeal articulators may be refined as children acquire the voicing contrast.
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