Volume 106, Issue 4, October 1999
Index of content:
- SPEECH PRODUCTION 
106(1999); http://dx.doi.org/10.1121/1.427946View Description Hide Description
Tamil is unusual among the world’s languages in that some of its dialects have five contrasting liquids. This paper focuses on the characterization of these sounds in terms of articulatory geometry and kinematics, as well as their articulatory-acoustic relations. This study illustrates the use of multiple techniques—static palatography, magnetic resonance imaging(MRI), and magnetometry (EMMA)—for investigating both static and dynamic articulatory characteristics using a single native speaker of Tamil. Dialectal merger and neutralization phenomena exhibited by the liquids of Tamil are discussed. Comparisons of English /ɹ/ and /l/ with Tamil provide evidence for generality in underlying mechanisms of rhotic and lateral production. The articulatory data justify the postulation of a class of rhotics and a class of laterals in Tamil, but do not provide evidence in favor of a larger class of liquids. Such a superclass appears to have largely an acoustic basis.
Viscoelastic shear properties of human vocal fold mucosa: Measurement methodology and empirical results106(1999); http://dx.doi.org/10.1121/1.427947View Description Hide Description
A standard method for the empirical rheological characterization of viscoelastic materials was adopted to measure the viscoelastic shear properties of human vocal-fold mucosal tissues (the superficial layer of lamina propria). A parallel-plate rotational rheometer was employed to measureshear deformation of viscoelastictissue samples, which were deformed between two rigid circular plates rotating in small-amplitude sinusoidal oscillations. Elastic and viscous shear moduli of the samples were then quantified as a function of oscillation frequency (0.01 to 15 Hz) based on shear stresses and strains recorded by the rheometer. Data were obtained from 15 excised human larynges (10 male and 5 female). Results showed that the elastic shear modulus μ and the damping ratio ζ of human vocal-fold mucosa were relatively constant across the range of frequencies observed, while the dynamic viscosity η decreased monotonically with frequency (i.e., shear thinning). Intersubject differences in μ and η as large as an order of magnitude were observed, part of which may reflect age-related and gender-related differences. Some molecular interpretations of the findings are discussed.
106(1999); http://dx.doi.org/10.1121/1.427948View Description Hide Description
A locus equation plots the frequency of the second formant at vowel onset against the target frequency of the same formant for the vowel in a consonant–vowel sequence, across different vowel contexts. It has generally been assumed that the slope of the locus equation reflects the degree of coarticulation between the consonant and the vowel, with a steeper slope showing more coarticulation. This study examined the articulatory basis for this assumption. Four subjects participated and produced VCV sequences of the consonants /b, d, g/ and the vowels /i, a, u/. The movements of the tongue and the lips were recorded using a magnetometer system. One articulatory measure was the temporal phasing between the onset of the lip closing movement for the bilabial consonant and the onset of the tongue movement from the first to the second vowel in a VCV sequence. A second measure was the magnitude of the tongue movement during the oral stop closure, averaged across four receivers on the tongue. A third measure was the magnitude of the tongue movement from the onset of the second vowel to the tongue position for that vowel. When compared with the corresponding locus equations, no measure showed any support for the assumption that the slope serves as an index of the degree of coarticulation between the consonant and the vowel.
Effects of syllable-initial voicing and speaking rate on the temporal characteristics of monosyllabic words106(1999); http://dx.doi.org/10.1121/1.427949View Description Hide Description
Two speech production experiments tested the validity of the traditional method of creating voice-onset-time (VOT) continua for perceptual studies in which the systematic increase in VOT across the continuum is accompanied by a concomitant decrease in the duration of the following vowel. In experiment 1, segmental durations were measured for matched monosyllabic words beginning with either a voiced stop (e.g., big, duck, gap) or a voiceless stop (e.g., pig, tuck, cap). Results from four talkers showed that the change from voiced to voiceless stop produced not only an increase in VOT, but also a decrease in vowel duration. However, the decrease in vowel duration was consistently less than the increase in VOT. In experiment 2, results from four new talkers replicated these findings at two rates of speech, as well as highlighted the contrasting temporal effects on vowel duration of an increase in VOT due to a change in syllable-initial voicing versus a change in speaking rate. It was concluded that the traditional method of creating VOT continua for perceptual experiments, although not perfect, approximates natural speech by capturing the basic trade-off between VOT and vowel duration in syllable-initial voiced versus voiceless stop consonants.