Volume 123, Issue 3, March 2008
Index of content:
- SPEECH PRODUCTION 
123(2008); http://dx.doi.org/10.1121/1.2831739View Description Hide Description
In this study, a biphasic theory is applied to investigate the viscoelastic behaviors of vocal fold lamina propria during stress relaxation. The vocal fold lamina propria tissue is described as a biphasic material composed of a solid phase and an interstitial fluid phase. The biphasic theory reveals the interaction between the solid and the fluid. For the one-dimensional case, the analytical solutions of solid displacement, fluid velocity, and stress are derived. The biphasic theory predicts the stress relaxation of the vocal fold lamina propria. The quasilinear viscoelastic model as well as its higher-order elastic parameters can be derived from this biphasic theory. Furthermore, the fluid is found to support the majority of the stress at the early stage of stress relaxation; however, when the time becomes sufficiently large, the solid eventually bears all the stress. The early fluid stress support is much higher than the eventual solid support and may be important for understanding the effects of dehydration on tissue damage. By considering the solid-fluid structure of the vocal fold lamina propria, the biphasic theory allows for a more physical theory of tissue viscoelasticity than a single phase solid description and may provide a valuable physical mechanism for the observed vocal fold rheologic behaviors.
123(2008); http://dx.doi.org/10.1121/1.2832328View Description Hide Description
The effect of the pressure recovery at glottal exit is introduced to modify the one-mass model. Using the modified one-mass model, the phonation critical condition, including phonation threshold pressure and phonation threshold flow, is analyzed by using the small-amplitude oscillation theory. It is found that the phonation threshold pressure is not sensitive to the change of the prephonatory glottal width at a wide glottal gap. This result agrees with previous experimental observations and suggests that the low slope of dependence of phonation threshold pressure on prephonatory gap found by Chan and Titze [J. Acoust. Soc. Am.119, 2351–2362 (2006)] could be a consequence of the pressure recovery effect at the glottal exit. In addition, it is predicted that the phonation threshold flow is always significantly increased with the prephonatory gap even at a wide prephonatory glottal gap. Therefore, the phonation threshold flow has an advantage in assessing the phonatory system at a wide prephonatory gap in comparison with the phonation threshold pressure. The phonation threshold flow can be a useful aerodynamic parameter for pathological conditions in which the incomplete glottal gap is often seen.
Investigation of a glottal related harmonics-to-noise ratio and spectral tilt as indicators of glottal noise in synthesized and human voice signals123(2008); http://dx.doi.org/10.1121/1.2832651View Description Hide Description
The harmonics-to-noise ratio (HNR) of the voiced speech signal has implicitly been used to infer information regarding the turbulent noise level at the glottis. However, two problems exist for inferring glottalnoise attributes from the HNR of the speech wave form: (i) the measure is fundamental frequency dependent for equal levels of glottalnoise, and (ii) any deviation from signal periodicity affects the ratio, not just turbulent noise. An alternative harmonics-to-noise ratio formulation [glottal related HNR (GHNR’)] is proposed to overcome the former problem. In GHNR’ a mean over the spectral range of interest of the HNRs at specific harmonic/between-harmonic frequencies (expressed in linear scale) is calculated. For the latter issue [(ii)] two spectral tilt measures are shown, using synthesis data, to be sensitive to glottalnoise while at the same time being comparatively insensitive to other glottal aperiodicities. The theoretical development predicts that the spectral tilt measures reduce as noise levels increase. A conventional HNR estimator, GHNR’ and two spectral tilt measures are applied to a data set of 13 pathological and 12 normal voice samples. One of the tilt measures and GHNR’ are shown to provide statistically significant differentiating power over a conventional HNR estimator.
Development and evaluation of methods for assessing tone production skills in Mandarin-speaking children with cochlear implants123(2008); http://dx.doi.org/10.1121/1.2832623View Description Hide Description
The aim of the study was (1) to develop methods for evaluating tone production of children with cochlear implants (CIs) who speak Mandarin Chinese and (2) to evaluate the efficacy of using these methods to assess tone production. The subjects included two groups of native-Mandarin-Chinese-speaking children: 14 prelingually deafened children who had received CIs and 61 normal-hearing (NH) children as controls. The acoustic analysis focused on quantification of the degree of differentiation among lexical tones based on tonal ellipses and the overall similarity of tone contours produced by the children with CIs to normative contours derived from the 61 NH children. An artificial neural network was used to recognize tones produced by the children with CIs after trained with tone tokens produced by the NH children. Finally, perceptual judgments on the tone production of both groups were obtained from eight native-Mandarin-speaking NH adults to evaluate the efficacy of the methods. The results showed that all measures using the acoustic, neural-network, and perceptual analyses were highly correlated with each other and could be used to effectively evaluate tone production of children with CIs.