The control of aerodynamics, acoustics, and perceptual characteristics during speech production.

One of the most important areas of study in speech motor control is the identification of control variables, the variables controlled by the nervous system during motor tasks. The current study examined two hypotheses regarding control variables in speech production: (1) pressure and resistance in the vocal tract are controlled, and (2) perceptual and acoustic accuracy are controlled. Aerodynamic and acoustic data were collected on 20 subjects in three conditions, normally (NT), with an open air pressure bleed tube in place (TWB), and with a closed bleed tube in place (TNB). The voice recordings collected from the speakers in the production study were used in the perceptual study. Results showed that oral pressure (Po) was significantly lower in the TWB condition than in the NT and TNB conditions. The Po in the TWB condition seemed to be related to maintenance of subglottal pressure (Ps). Examination of the perceptual and acoustic data indicated that perceptual accuracy for [a] was achieved by maintaining Ps to preserve a steady sound pressure level, fundamental frequency, and voicing. Overall, it appeared speakers controlled pressure in compensating, but for the ultimate goal of maintaining acoustic and perceptual accuracy.