A dynamic mechanical model of the human larynx and vocal tract has been developed to investigate its acoustic and fluid dynamic behaviour during sustained vowel production. The model comprises a cylindrical duct, open at one end, with a controlled air flow introduced at the other. The flow entering the duct is modulated by the periodic opening and closing of pair of electro-mechanically driven shutters. Far field measurements of the radiated pressure have shown that the model generates sound which has a spectral distribution that corresponds, at low frequencies, to that of an open vowel. However the spectral amplitudes were somewhat lower than voiced speech sounds normally generated at the same low rate. The addition of an orifice plate to reduce the duct exit area was found to increase the level of the radiated sound and to modify the spectral distribution somewhat. The flow distribution throughout the model duct has been measured using hot wire anemometry. The velocity distribution measured in the model was found to correspond to that measured in the oral cavity of four live subjects. Calibrate pressure measurements at the duct wall have been used define the associated pressure field within the duct. The pressure distribution found within the model corresponded to that measured in vivo by other researchers. The velocity within the duct was shown to be associated with contributions from three separate velocity fields, the rotational acoustic particle velocity and a rotational velocity field due to vortex development at the exit to the shutters. It was shown that the rotational velocity disturbance convected along the duct at approximately the local mean flow velocity. Comparison of prediction with measurement of the radiated sound fields showed that the presence of a rotational velocity field at the duct exit made a significant contribution to the radiated sound pressure level. A discussion is included as to whether acoustic sources, associated with the rotational flow, exists at area discontinuities in the vocal tract in addition to the generally accepted acoustic source due to fluctuating mass flow at the glottal exit. The influence of the Rotheberg Mask on the flow and acoustic behaviour of the model was investigated in some detail. Measurements show that the velocity field was almost unaltered, but the fluctuating pressure amplitudes were greatly reduced. Corresponding reductions were found in the radiated acoustic power with further reductions apparently due to the suppression of the rotational flow sources by the mask.

abstract: Distorted vowel production is a hallmark characteristic of dysarthric speech, irrespective of the underlying neurological condition or dysarthria diagnosis. A variety of acoustic metrics have been used to study the nature of vowel production deficits in dysarthria; however, not all demonstrate sensitivity to the exhibited deficits. Less attention has been paid to quantifying the vowel production deficits associated with the specific dysarthrias. Attempts to characterize the relationship between naturally degraded vowel production in dysarthria with overall intelligibility have met with mixed results, leading some to question the nature of this relationship. It has been suggested that aberrant vowel acoustics may be an index of overall severity of the impairment and not an "integral component" of the intelligibility deficit. A limitation of previous work detailing perceptual consequences of disordered vowel acoustics is that overall intelligibility, not vowel identification accuracy, has been the perceptual measure of interest. A series of three experiments were conducted to address the problems outlined herein. The goals of the first experiment were to identify subsets of vowel metrics that reliably distinguish speakers with dysarthria from non-disordered speakers and differentiate the dysarthria subtypes. Vowel metrics that capture vowel centralization and reduced spectral distinctiveness among vowels differentiated dysarthric from non-disordered speakers. Vowel metrics generally failed to differentiate speakers according to their dysarthria diagnosis. The second and third experiments were conducted to evaluate the relationship between degraded vowel acoustics and the resulting percept. In the second experiment, correlation and regression analyses revealed vowel metrics that capture vowel centralization and distinctiveness and movement of the second formant frequency were most predictive of vowel identification accuracy and overall intelligibility. The third experiment was conducted to evaluate the extent to which the nature of the acoustic degradation predicts the resulting percept. Results suggest distinctive vowel tokens are better identified and, likewise, better-identified tokens are more distinctive. Further, an above-chance level agreement between nature of vowel misclassification and misidentification errors was demonstrated for all vowels, suggesting degraded vowel acoustics are not merely an index of severity in dysarthria, but rather are an integral component of the resultant intelligibility disorder. / Dissertation/Thesis / Ph.D. Speech and Hearing Science 2012

Though previous research has documented the Southern Vowel Shift (SVS) in Alabama and Tennessee, none has focused on Mississippi. Also, the majority of research has focused on European-Americans. In this study, data was collected from women from northern and central Mississippi, with central residents evenly recruited from urban and rural areas. Of these, 15 were European-American and 19 were African-American. Participants read a word list including target vowels in the b_d frame. F1, F2, and vector length were analyzed to determine to what extent participants exhibited the SVS and Back Vowel Fronting. For the SVS, there were effects such that central residents shifted more than northern, rural residents shifted more than urban, and African-American residents shifted more than European-American. European-American women fronted /u/ and /o/ more than African-American women. These results suggest that African-American women from Mississippi do participate in the SVS but are not fronting their back vowels.

No description available.