Speech motor coordination and control: evidence from lip, jaw, and laryngeal movements

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.