Motor control of velopharyngeal structures during vowel production

This investigation was designed to measure the ability of normal adult speakers to exert voluntary control over velopharyngeal positioning. Speakers were asked to phonate the vowels [a] and [i] at 50 percent and 75 percent of complete velopharyngeal closure, using visual feedback of velopharyngeal opening and closing gestures from a phototransducer. The musculature of the velopharyngeal mechanism was hypothesized to act as a coordinated system that may demonstrate both motor flexibility and plasticity (Folkins, 1985) when forced to function in a novel way. Evidence of both motor system responses to a novel speaking condition was observed. Speakers were able either to phonate at intermediate closure levels without having to learn new motor rules, or to learn new rules for velopharyngeal muscle activation that resulted in the ability over time to position the velopharyngeal mechanism appropriately. As such, support is derived for the notion (Folkins, 1985) that speakers develop motor rules or coordinative structures involving the velopharyngeal mechanism that govern velopharyngeal movement. The characteristics of this coordinative structure framework has not yet been described, however, and are the subject of ongoing research efforts.