Volume 107, Issue 1, January 2000
Index of content:
- SPEECH PRODUCTION 
107(2000); http://dx.doi.org/10.1121/1.428323View Description Hide Description
Previous studies have shown that voice fundamental frequency is modified by changes in the pitch of vocal feedback and have demonstrated that the audio–vocal control system has both open- and closed-loop control properties. However, the extent to which this system operates in closed-loop fashion may have been underestimated in previous work. Because the step-type stimuli used were very rapid, and people are physically unable to change their voice as rapidly as the stimuli, feedback responses might have been reduced or suppressed. In the present study, pitch-shift stimuli, consisting of a disparity between voice and feedback pitch of varying ramp onset velocities, were presented to subjects vocalizing a steady /ah/ sound to examine the effect of stimulus onset on voice responses. Results showed that response velocity covaried with stimulus velocity. Response latency and time of the peak response decreased with increases in stimulus velocity, while response magnitude decreased. A simple feedback model reproduced most features of these responses. These results strongly support previous suggestions that the audio-vocal system monitors auditory feedback and, through closed-loop negative feedback, adjusts voice so as to cancel low-level fluctuations in
Viscoelastic shear properties of human vocal fold mucosa: Theoretical characterization based on constitutive modeling107(2000); http://dx.doi.org/10.1121/1.428354View Description Hide Description
The viscoelastic shear properties of human vocal fold mucosa (cover) were previously measured as a function of frequency [, J. Acoust. Soc. Am. 106, 2008–2021 (1999)], but data were obtained only in a frequency range of 0.01–15 Hz, an order of magnitude below typical frequencies of vocal fold oscillation (on the order of 100 Hz). This study represents an attempt to extrapolate the data to higher frequencies based on two viscoelastictheories, (1) a quasilinear viscoelastictheory widely used for the constitutive modeling of the viscoelastic properties of biological tissues [Biomechanics (Springer-Verlag, New York, 1993), pp. 277–292], and (2) a molecular (statistical network) theory commonly used for the rheological modeling of polymeric materials [24, 1007–1018 (1991)]. Analytical expressions of elastic and viscous shear moduli, dynamic viscosity, and damping ratio based on the two theories with specific model parameters were applied to curve-fit the empirical data. Results showed that the theoretical predictions matched the empirical data reasonably well, allowing for parametric descriptions of the data and their extrapolations to frequencies of phonation.
107(2000); http://dx.doi.org/10.1121/1.428324View Description Hide Description
Newly developed glottographic sensors, utilizing high-frequency propagating electromagnetic waves, were compared to a well-established electroglottographic device. The comparison was made on four male subjects under different phonation conditions, including three levels of vocal fold adduction (normal, breathy, and pressed), three different registers (falsetto, chest, and fry), and two different pitches. Agreement between the sensors was always found for the glottal closure event, but for the general wave shape the agreement was better for falsetto and breathy voice than for pressed voice and vocal fry. Differences are attributed to the field patterns of the devices. Whereas the electroglottographic device can operate only in a conduction mode, the electromagnetic device can operate in either the forward scattering (diffraction) mode or in the backward scattering (reflection) mode. Results of our tests favor the diffraction mode because a more favorable angle imposed on receiving the scattered (reflected) signal did not improve the signal strength. Several observations are made on the uses of the electromagneticsensors for operation without skin contact and possibly in an array configuration for improved spatial resolution within the glottis.