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Changes in Articulator Movement Variability During Phonemic Development: A Longitudinal Study

Contact author: Maria I. Grigos, Department of Speech Language Pathology and Audiology, New York University, 665 Broadway, Suite 918, New York, NY 10003. E-mail: maria.grigos{at}nyu.edu.

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.

KEY WORDS: variability, articulator movement, development, voice onset time

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