Vocal shadowing under conditions of normal and altered laryngeal sensation

Five adult male subjects vocally matched the pitches of tones in a steady-state tone matching task (SSTMT) and vocally shadowed frequency changes in a frequency modulated tone matching task (FMTMT). Matching was done in both a normal condition and a condition of topical anesthesia of the laryngeal mucosa. Pitch matching accuracy was not seriously altered in the anethesia condition, but anesthetized subjects required more time and had slower velocities in effecting transitions between tones on the FMTMT, as compared to normal. In both conditions there was a direct proportionality between interval size and each of the time and velocity variables examined, while frequency lowering was generally faster than frequency raising. Analysis of subject response strategies on the FMTMT revealed recurring patterns, described here as Overshoot, Undershoot, Oscillate and Hit. Fewer Hit, and more Oscillate, patterns were observed for the anesthesia condition as compared to normal. It was concluded that the FMTMT, as compared to the SSTMT, required finer and more rapid laryngeal control to coordinate respiratory driving pressures and glottal resistance, and hence was more susceptible to impairment of the laryngeal mucosal reflexogenic system. Implications of the data for modeling certain mechanical and physiological aspects of laryngeal control are discussed.