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Biomedical subjects

R S McGowan

Publications and source records attributed to R S McGowan.

10 recordsLinked to original sources
PubMed1999

Vocal tract normalization for midsagittal articulatory recovery with analysis-by-synthesis.

A method is presented that accounts for differences in the acoustics of vowel production caused by human talkers' vocal-tract anatomies and postural settings. Such a method is needed by an analysis-by-synthesis procedure designed to recover midsagittal articulatory movement from speech acoustics because the procedure employs an articulatory model as an internal model. The normalization procedure involves the adjustment of parameters of the articulatory model that are not of interest for the midsagittal movement recovery procedure. These parameters are adjusted so that acoustic signals produced by the human and the articulatory model match as closely as possible over an initial set of pairs of corresponding human and model midsagittal shapes. Further, these initial midsagittal shape correspondence need to be generalized so that all midsagittal shapes of the human can be obtained from midsagittal shapes of the model. Once these procedures are complete, the midsagittal articulatory movement recovery algorithm can be used to derive model articulatory trajectories that, subsequently, can be transformed into human articulatory trajectories. In this paper the proposed normalization procedure is outlined and the results of experiments with data from two talkers contained in the X-ray Microbeam Speech Production Database are presented. It was found to be possible to characterize these vocal tracts during vowel production with the proposed procedure and to generalize the initial midsagittal correspondences over a set of vowels to other vowels. The procedure was also found to aid in midsagittal articulatory movement recovery from speech acoustics in a vowel-to-vowel production for the two subjects.

Humans↗
PubMed1996

Task dynamic and articulatory recovery of lip and velar approximations under model mismatch conditions.

An algorithm for recovering task dynamics and speech articulator movements from speech acoustics was tested under various model mismatch conditions. There was evidence of articulatory compensation to recover tract-variable (constriction) trajectories in speech produced with a lip approximation under sufficiently constrained conditions. However, in more extensive studies of lip and velar approximations, the recovered tract-variable trajectories were also different from those of the data-producing utterance. This phenomenon can occur because the matching criterion in the analysis-by-synthesis procedure is an acoustic criterion and the correspondence between the tract-variable trajectories and the acoustic output is not exact. While there may be some tract-variable compensation to attain a good acoustic match, there is evidence of a correspondence between how well the tract-variable trajectories match and how well the formant frequencies match in particular instances.

Humans↗
PubMed1995

The effect of gas density on glottal vibration and exit jet particle velocity.

Although theoretical studies include a term for gas density in their mathematical descriptions of glottal aerodynamics, the effect of gas density on glottal vibration has not been examined empirically. In this study, an in vivo canine model was used to evaluate the effect of gas density on glottal vibration by comparing phonation with air and helium. With gas flow and nerve stimulation held constant, phonation with helium resulted in an increased exit jet particle velocity for helium (45 m/s) compared to air (34 m/s). However, the measured increase in helium velocity was less than predicted by a proportional relationship between transglottal pressure and dynamic pressure. This difference could be due to a change in the constant of proportionality or in the dynamic pressure loss coefficient associated with the use of helium.

Animals↗
PubMed1993

Extracting dynamic parameters from speech movement data.

A quantitative characterization of articulatory movements, using the parameter values of a linear second-order dynamical system, was developed in order to compare classes of movements, in particular, classes defined by linguistic factors such as syllable position, stress, and vowel quality. Movements of the lower lip in utterances such as ['bibebib] and [babe'bab] were partitioned into sections ("windows") in two ways: at successive displacement peaks and valleys, and at the right edge of plateau regions around such extreme values. The linguistic factors affected natural frequency in similar ways regardless of whether damping ratio was permitted to vary or held fixed at one of several different values. Damping ratio was generally unaffected by the linguistic factors. For the most part, the type of partition or window did not affect the patterns of the results, with the exception of the closing gesture out of the reduced syllable.

Adult↗
PubMed1992

Tongue-tip trills and vocal-tract wall compliance.

The effect of vocal-tract wall compliance on tongue-tip trills is to create a favorable pressure-flow relation at the tongue tip for sustained vibration. The governing equations are derived for a model based on this mechanism, and data on unvoiced trills are used to help set parameters for a numerical simulation of the model.

Compliance↗
PubMed1990

Acoustic measurements of men's and women's voices: a study of context effects and covariation.

Several acoustic measures of laryngeal activity were made on adult speech to help answer two questions left unresolved by previous work: (1) how each measure varies, if at all, with phonetic structure, and (2) what aspect of laryngeal activity each measure specifies. Speech samples of 15 syllables (three vowels in five prevocalic consonantal contexts) were collected from men and women at two times of the day (early morning and late afternoon). Eight measurements were made, mainly on slices extracted from the middle of the vocalic portions, and inferential and correlational statistics were applied to these measures. Results of the inferential tests indicated differences between men and women in how laryngeal adjustments are made, affecting relative amounts of vocal jitter and spectral tilt of the voicing source. In addition, the voicing and manner characteristics of the prevocalic consonant were found to affect fundamental frequency, cycle-to-cycle perturbations, and amount of aspiration noise. To a lesser extent, vowel height and front/back tongue placement also affected these acoustic source characteristics. Results of the correlational tests showed that different laryngeal mechanisms contributed differentially to signal-to-noise ratios for men and women, and these mechanisms were more greatly affected by fundamental frequency for men's samples. Finally, various acoustic measures of laryngeal noise were found to be related to the same underlying mechanism.

Adult↗
PubMed1989

The emergence of phonetic segments: evidence from the spectral structure of fricative-vowel syllables spoken by children and adults.

A variety of evidence, including the speech errors of normal and aphasic speakers, and the metalinguistic skills of literate individuals, demonstrates that speech has an underlying phonemic organization. However, we know little about how this organization develops in the child. The purpose of the present study was to test the hypothesis that phoneme-sized phonetic segments emerge as functional units of perceptuomotor control from the child's gradual reorganization of the gestures forming its early words or syllables. We investigated the acoustic structure of syllables produced by young children and adults. Fricative-vowel syllables spoken by 40 subjects (eight adults and eight children at each of the ages 3, 4, 5, and 7 years) were analyzed acoustically to determine how well different syllables-initial fricatives were contrasted and how strongly they were affected by vocalic context. Results indicated two independent developmental trends: The extent to which speakers differentiated between /integral of/ and /s/ increased with age, while the extent to which they coarticulated each fricative with its following vowel decreased. The results support the hypothesis that children initially organize their speech gestures over a domain at least the size of the syllable and only gradually differentiate the syllable into patterns of gestures more closely aligned with its perceived segmental components.

Adult↗
PubMed1988

An aeroacoustic approach to phonation.

A fluid mechanical, or aeroacoustic, point of view is followed to study possible sources of sound during phonation. Concentration is on two features of the vocal tract during phonation: abrupt area change from the glottis to the vocal tract and the finite length of the vocal tract. With these features, a source of sound distinct from the volume velocity source can be identified and a preliminary account of its effect on the acoustic field given. This source of sound is an oscillating force resulting from an interaction of rotational fluid motion with itself. Because of the schematic nature of the geometry of the model used here, this source may be considerably modified in actual phonation. It is concluded that specification of volume velocity is not enough to specify the source during phonation, even neglecting source-tract interaction.

Humans↗
PubMed1988

Differences in fricative production between children and adults: evidence from an acoustic analysis of /sh/ and /s/.

Speech samples of 12 speakers (8 children and 4 adults) producing the fricatives /s/ and/sh/ followed by the vowels /i/ and /u/ were analyzed to locate the major spectral prominences. Results showed that the fricative low-frequency prominences for children's samples differed from those of adults in three important ways: (1) They were generally higher in frequency; (2) they were greater in amplitude relative to higher frequency regions; and (3) they showed greater effects of vowel context. The first finding can be explained by a simple scaling of adult models of fricative production to accommodate children's smaller vocal tracts. The other two findings suggest, however, that there are other anatomical and articulatory differences between children and adults affecting fricative production. The data presented here suggest that one important difference may be the relative sizes of the fricative constriction and the glottal opening.

Adult↗