Time normalization of voice signals using functional data analysis.

The harmonics-to-noise ratio (HNR) has been used to quantify the waveform irregularity of voice signals [Yumoto et al., J. Acoust. Soc. Am. 71, 1544-1550 (1982)]. This measure assumes that the signal consists of two components: a harmonic component, which is the common pattern that repeats from cycle-to-cycle, and an additive noise component, which produces the cycle-to-cycle irregularity. It has been shown [J. Qi, J. Acoust. Soc. Am. 92, 2569-2576 (1992)] that a valid computation of the HNR requires a nonlinear time normalization of the cycle wavelets to remove phase differences between them. This paper shows the application of functional data analysis to perform an optimal nonlinear normalization and compute the HNR of voice signals. Results obtained for the same signals using zero-padding, linear normalization, and dynamic programming algorithms are presented for comparison. Functional data analysis offers certain advantages over other approaches: it preserves meaningful features of signal shape, produces differentiable results, and allows flexibility in selecting the optimization criteria for the wavelet alignment. An extension of the technique for the time normalization of simultaneous voice signals (such as acoustic, EGG, and airflow signals) is also shown. The general purpose of this article is to illustrate the potential of functional data analysis as a powerful analytical tool for studying aspects of the voice production process.

A model of facial biomechanics for speech production.

Modeling the peripheral speech motor system can advance the understanding of speech motor control and audiovisual speech perception. A 3-D physical model of the human face is presented. The model represents the soft tissue biomechanics with a multilayer deformable mesh. The mesh is controlled by a set of modeled facial muscles which uses a standard Hill-type representation of muscle dynamics. In a test of the model, recorded intramuscular electromyography (EMG) was used to activate the modeled muscles and the kinematics of the mesh was compared with 3-D kinematics recorded with OPTOTRAK. Overall, there was a good match between the recorded data and the model's movements. Animations of the model are provided as MPEG movies.

A theoretical study of the hysteresis phenomenon at vocal fold oscillation onset-offset.

This paper presents a theoretical study on the differences in the biomechanical parameters of the vocal folds between oscillation onset and offset. The dynamics of the oscillation is analyzed from the perspective of the theory of nonlinear dynamical systems, using a mucosal wave model of the vocal folds with the subglottal pressure and the vocal fold half-width as control parameters. It is shown that the oscillation onset occurs through a Hopf bifurcation of the subcritical type, at which an unstable limit cycle is generated. Also, the oscillation offset occurs at a cyclic fold bifurcation, at which the unstable limit cycle and a stable limit cycle (the actual vocal fold oscillation) coalesce and cancel each other. Both bifurcations combine to form an "oscillation hysteresis" phenomenon, common in cases of flow-induced oscillations. An analytical expression for the onset/offset ratio of parameters is derived. The onset/offset ratio is in the range of 0.5-1, in agreement with the experimental evidence. This value depends on the phase delay in motion of the upper edge of the vocal folds versus the lower edge, and on the particular model adopted for airflow separation within the glottis.

Optimal glottal configuration for ease of phonation.

Recent experimental studies have shown the existence of optimal values of the glottal width and convergence angle, at which the phonation threshold pressure is minimum. These results indicate the existence of an optimal glottal configuration for ease of phonation, not predicted by the previous theory. In this paper, the origin of the optimal configuration is investigated using a low dimensional mathematical model of the vocal fold. Two phenomena of glottal aerodynamics are examined: pressure losses due to air viscosity, and air flow separation from a divergent glottis. The optimal glottal configuration seems to be a consequence of the combined effect of both factors. The results agree with the experimental data, showing that the phonation threshold pressure is minimum when the vocal folds are slightly separated in a near rectangular glottis.

On the registration of time and the patterning of speech movements.

In order to study speech coordination we frequently average kinematic and other physiological signals. The averages are assumed to be more representative of the underlying patterns of production than individual records. In this note we outline different approaches to averaging and present a new nonlinear normalization technique that offers better information than ensemble averaging, linear normalization, or feature alignment methods. We suggest that this technique provides a clear estimation of pattern shape while preserving information on the variation over time.

The minimum lung pressure to sustain vocal fold oscillation.

In previous experimental studies it has been observed that the minimum lung pressure to sustain vocal fold oscillation after its onset is lower than the threshold pressure needed to initiate it. This phenomenon is studied analytically using a previous body-cover model of the vocal folds and applying the describing function method to the general case of large amplitude oscillations. It is shown that the phenomenon is a consequence of the nonlinear characteristic of the effective aerodynamic damping introduced by the air pressure acting on the vocal folds. The results predict a value for minimum sustaining pressure equal to half the threshold pressure for a rectangular prephonatory glottis, which is in the order of experimental results.

Characteristic recovery time of an erythrocyte from an extensional deformation.

An analytical expression for the characteristic recovery time of an erythrocyte subject to an extensional deformation is derived using a previous nonlinear Kelvin-Voigt model. The recovery time thus obtained depends on the initial deformation in agreement with experimental observations, as a result of the nonlinearity of the model. The validity of the analytical results is confirmed using previous experimental data.

Influence of oral contraceptives on the acute effect of amphetamine on the hepatic endoplasmic reticulum of the rat.

The interaction between amphetamine and synthetic oral contraceptive steroids have been studied in the female rat. A progestational agent, quingestanol acetate, and a standard combination contraceptive (quingestanol acetate/ethynyl estradiol) were given with and without the concurrent administration of amphetamine. Steroid treatments increased the activity of some drug-metabolizing enzymes (aminopyrine N-demethylase, coumarin 3- hydroxylase, hexobarbital oxidase). Other parameters measured remained unaltered (glucose-6-phosphatase, aniline hydroxylase, cytochrome c reductase, cytochrome P 450, microsomal protein and phospholipid contents). Amphetamine treatment alone raised some drug-metabolizing enzymes (coumarin 3-hydroxylase, hexobarbital oxidase), increased microsomal phospholipid content and de novo synthesis, but elicited no effect on other enzymes measured. Amphetamine and quingestanol acetate given together significantly increased some drug metabolizing enzymes while the simultaneous treatment with combined steroids and amphetamine showed the most pronounced action. These experiments thus revealed that at least in the liver of the female rat, amphetamine elicited no overt hepatotoxicity, rather, brought about a weak inductive action of drug metabolizing enzymes. The application of steroid hormones also raised drug metabolism and the interaction between amphetamine and contraceptive steroids showed additive effects.