title: Changes in articulator movement variability during phonemic development: a longitudinal study.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
authors.affiliation: Department of Speech Language Pathology and Audiology, New York University, 665 Broadway, Suite 918, New York, NY 10003, USA. maria.grigos@nyu.edu
authors.forename: Maria I
authors.initials: MI
authors.lastname: Grigos
mesh_terms: D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007223:Infant; D007568:Jaw / Q000502:physiology*; D007804:Language Development; D008046:Lip / Q000502:physiology*; D008297:Male; D015233:Models, Statistical; D009043:Motor Activity; D010700:Phonetics; D013060:Speech / Q000502:physiology*; D013068:Speech Production Measurement