Journal of Neuroscience, Vol 14, 6585-6597, Copyright © 1994 by Society for Neuroscience
Speech motor coordination and control: evidence from lip, jaw, and laryngeal movements
VL Gracco and A Lofqvist
Haskins Laboratories, New Haven, Connecticut 06510.
The movements of the lower lip, jaw, and larynx during speech were examined
for two different speech actions involving oral closing for /p/ and oral
constriction for /f/. The initial analysis focused on the manner in which
the different speech articulators were coordinated to achieve sound
production. It was found that the lip, jaw, and laryngeal movements were
highly constrained in their relative timing apparently to facilitate their
coordination. Differences were noted in the degree to which speech
articulator timing covaried dependent on the functional characteristics of
the action. Movements associated with coordinating multiple articulators
for a single sound were more highly constrained in their relative timing
than were movements associated with sequencing of individual sounds. The
kinematic patterns for the different articulators were found to vary in a
number of systematic ways depending on the identity of the sound being
produced, the phonetic context surrounding the target sound, and whether
one versus two consonants were produced in sequence. The results are
consistent with an underlying organization reflecting the construct of the
phoneme. It is suggested that vocal tract actions for the sounds of the
language are stored in memory as motor programs and sequenced together into
larger meaningful units during speaking. Speech articulator motion for the
different vowel sounds was found to be influenced by the identity of the
following consonant, suggesting that speech movements are modified in
chunks larger than the individual phonetic segments. It appears that speech
production is a hierarchical process with multiple levels of organization
transforming cognitive intent into coherent and perceptually identifiable
sound sequences.