Volume 126, Issue 2, August 2009
Index of content:
- SPEECH PRODUCTION 
Analysis of flow-structure interaction in the larynx during phonation using an immersed-boundary method126(2009); http://dx.doi.org/10.1121/1.3158942View Description Hide Description
A recently developed immersed-boundary method is used to model the flow-structure interaction associated with the human phonation. The glottal airflow is modeled as a two-dimensional incompressible flow driven by a constant subglottal pressure, and the vocal folds are modeled as a pair of three-layered, two-dimensional, viscoelastic structures. Both the fluid dynamics and viscoelasticity are solved on fixed Cartesian grids using a sharp-interface immersed boundary method. It is found that the vibration mode and frequency of the vocal fold model are associated with the eigenmodes of the structures, and that the transition of the vibration mode takes place during onset of the sustained vibration. The computed glottal waveforms of the volume flux, velocity, and pressure are reasonably realistic. The glottalflow features an unsteady jet whose direction is deflected by the large-scale vortices in the supraglottal region. A detailed analysis of the flow and vocal fold vibrations is conducted in order to gain insights into the biomechanics of phonation.
126(2009); http://dx.doi.org/10.1121/1.3158816View Description Hide Description
The purpose of this study was to develop a method by which a vowel-consonant-vowel (VCV) utterance based on x-ray microbeam articulatory data could be separated into a vowel-to-vowel transition and a consonant superposition function. The result is a model that represents a vowel sequence as a time-dependent perturbation of the neutral vocal tract shape governed by coefficients of canonical deformation patterns. Consonants were modeled as superposition functions that can force specific portions of the vocal tract shape to be constricted or expanded, over a specific time course. The three VCVs [əpɑ], [ətɑ], and [əkɑ], produced by one female speaker, were analyzed and reconstructed with the developed model. They were shown to be reasonable approximations of the original VCVs, as assessed qualitatively by visual inspection and quantitatively by calculating rms error and correlation coefficients. This establishes a method for future modeling of other speech material.
The sensitivity of auditory-motor representations to subtle changes in auditory feedback while singing126(2009); http://dx.doi.org/10.1121/1.3158600View Description Hide Description
Singing requires accurate control of the fundamental frequency (F0) of the voice. This study examined trained singers’ and untrained singers’ (nonsingers’) sensitivity to subtle manipulations in auditory feedback and the subsequent effect on the mapping between F0 feedback and vocal control. Participants produced the consonant-vowel /ta/ while receiving auditory feedback that was shifted up and down in frequency. Results showed that singers and nonsingers compensated to a similar degree when presented with frequency-altered feedback (FAF); however, singers’ F0 values were consistently closer to the intended pitch target. Moreover, singers initiated their compensatory responses when auditory feedback was shifted up or down 6 cents or more, compared to nonsingers who began compensating when feedback was shifted up 26 cents and down 22 cents. Additionally, examination of the first 50 ms of vocalization indicated that participants commenced subsequent vocal utterances, during FAF, near the F0 value on previous shift trials. Interestingly, nonsingers commenced F0 productions below the pitch target and increased their F0 until they matched the note. Thus, singers and nonsingers rely on an internal model to regulate voice F0, but singers’ models appear to be more sensitive in response to subtle discrepancies in auditory feedback.