Volume 135, Issue 3, March 2014
Index of content:
- SPEECH PRODUCTION 
135(2014); http://dx.doi.org/10.1121/1.4864479View Description Hide Description
A direct numerical simulation of flow-structure interaction is carried out in a subject-specific larynx model to study human phonation under physiological conditions. The simulation results compare well to the established human data. The resulting glottal flow and waveform are found to be within the normal physiological ranges. The effects of realistic geometry on the vocal fold dynamics and the glottal flow are extensively examined. It is found that the asymmetric anterior-posterior laryngeal configuration produces strong anterior-posterior asymmetries in both vocal fold vibration and glottal flow which has not been captured in the simplified models. It needs to be pointed out that the observations from the current numerical simulation are only valid for the flow conditions investigated. The limitations of the study are also discussed.
135(2014); http://dx.doi.org/10.1121/1.4863646View Description Hide Description
An experiment was carried out to determine whether the level of the speech fluency disorder can be estimated by means of automatic acoustic measurements. These measures analyze, for example, the amount of silence in a recording or the number of abrupt spectral changes in a speech signal. All the measures were designed to take into account symptoms of stuttering. In the experiment, 118 audio recordings of read speech by Czech native speakers were employed. The results indicate that the human-made rating of the speech fluency disorder in read speech can be predicted on the basis of automatic measurements. The number of abrupt spectral changes in the speech segments turns out to be the most appropriate measure to describe the overall speech performance. The results also imply that there are measures with good results describing partial symptoms (especially fixed postures without audible airflow).
Three-year-olds' production of Australian English phonemic vowel length as a function of prosodic context135(2014); http://dx.doi.org/10.1121/1.4864292View Description Hide Description
Durational contrasts are used not only to signal phrasal boundaries and focused constituents, but also to make phonemic distinctions. Boundary and focus effects can therefore interact with phonemic length contrasts, presenting a challenge for learners. Boundary effects are most clearly seen in the syllable rhyme, where the nucleus and coda are longer in utterance-final compared to utterance-medial position, the magnitude of lengthening diminishing leftward from the end of the word. In the case of focus, where the nucleus and coda are also lengthened, the magnitude of lengthening diminishes rightwards toward the end of the word. The goal of this paper was therefore to compare productions of the phonemic vowel length contrast /ɐː/ vs /ɐ/ in adults and 3-yr-old children learning Australian English in the face of competing demands from boundary and focus lengthening. The results showed that the children maintain the /ɐː/ vs /ɐ/ contrast across prosodic contexts. They are also able to implement an adult-like pattern of boundary-related lengthening, but are still developing focus-related lengthening. The findings suggest that these 3-yr-olds have good command of the phonemic vowel length contrast, but are still fine-tuning language-specific aspects of temporal organization (i.e., the vowel-coda trading relationship) within the rhyme.
135(2014); http://dx.doi.org/10.1121/1.4863266View Description Hide Description
Although vocal folds are known to be anisotropic, the influence of material anisotropy on vocal fold vibration remains largely unknown. Using a linear stability analysis, phonation onset characteristics were investigated in a three-dimensional anisotropic vocal fold model. The results showed that isotropic models had a tendency to vibrate in a swing-like motion, with vibration primarily along the superior-inferior direction. Anterior-posterior (AP) out-of-phase motion was also observed and large vocal fold vibration was confined to the middle third region along the AP length. In contrast, increasing anisotropy or increasing AP-transverse stiffness ratio suppressed this swing-like motion and allowed the vocal fold to vibrate in a more wave-like motion with strong medial-lateral motion over the entire medial surface. Increasing anisotropy also suppressed the AP out-of-phase motion, allowing the vocal fold to vibrate in phase along the entire AP length. Results also showed that such improvement in vibration pattern was the most effective with large anisotropy in the cover layer alone. These numerical predictions were consistent with previous experimental observations using self-oscillating physical models. It was further hypothesized that these differences may facilitate complete glottal closure in finite-amplitude vibration of anisotropic models as observed in recent experiments.