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J R Westbury

Publications and source records attributed to J R Westbury.

11 recordsLinked to original sources
PubMed1998

Vowel posture normalization.

A simple normalization procedure was applied to point-parametrized articulatory data to yield quantitative speaker-general descriptions of "average" vowel postures. Articulatory data from 20 English and 8 Japanese speakers, drawn from existing x-ray microbeam database corpora, were included in the analysis. The purpose of the normalization procedure was to minimize the effects of differences in vocal tract size and shape on average postures derived from the raw data. The procedure resulted in a general reduction of cross-speaker variance in the y dimension of the normalized space, within both language groups. This result can be traced to a systematic source of variance in the y dimension of the raw data (i.e., palatal height) "successfully removed" from the normalized data. The procedure did not result in a comparable, general reduction in cross-speaker variance in the x dimension. This negative result can be traced partly to the new observation that some speakers within the English sample habitually placed their tongues in a fronted position for all vowels, whereas other speakers habitually placed their tongues in a rearward position. Methods for evaluating articulatory normalization schemes, and possible sources of interspeaker variability in vowel postures, are discussed.

Adult↗
PubMed1991

The significance and measurement of head position during speech production experiments using the x-ray microbeam system.

Head position and orientation are important variables during experiments conducted on the University of Wisconsin x-ray microbeam system, a nationally shared imaging facility for speech production research. Normally, the head is not restrained during experiments, in order to maximize the naturalness of speech performance, even though free head movements may have an adverse effect on the accuracy of kinematic data that are obtained. The basis for this effect is explained, and techniques for dealing with temporal variations in head position are described. Results obtained from a novel method for three-dimensional measurement of head position, applied to data sets recorded from six normal adult speakers during otherwise typical x-ray microbeam experiments, are summarized to convey some sense of the measurement error that can arise from deviations from a required head position. These measurements suggested that among these speakers, errors attributable to improper positioning of the head, and/or inadvertent head movements within or between trials, never exceeded 5%.

Computer Graphics↗
PubMed1988

Mandible and hyoid bone movements during speech.

Relatively little is known about the extent to which speech-related movements of the mandible and hyoid bone involve rotation and translation. Data were derived from an existing high-speed cineradiograph of 27 disyllables produced by a single adult male speaker of English to address this issue. Time histories of relative locations of both bony components of the mandibular system, expressed in terms equivalent to the sagittal-plane coordinates of two landmarks on each, were analyzed to determine (a) their respective ranges of position and orientation, (b) associations between selected segmental and suprasegmental variables, and subregions of those ranges, and (c) interdependencies between articulator rotation and landmark displacement. In general, data from this speaker, for the mandible and hyoid bone, are consistent with previous reports for the mandible alone, all of which suggest that rotational and translational components of their motions are sufficiently independent to warrant kinematic descriptions that treat both structures as rigid bodies moving in a plane.

Cineradiography↗
PubMed1984

Mandible movements during increasingly rapid articulations of single syllables: preliminary observations.

A previous study of mandible movements in normal speech [W.L. Nelson, J. Acoust. Soc. Am. Suppl. 1 68, S32 (1980)] suggested that the speech motor control process resulted in a relationship between movement time, distance, and peak velocity which implied (1) some adaptation to the physical effort required for the movement, and (2) that the force limit effective during speech was considerably below that which the mandibular muscles are capable of producing. In the present study, mandible movements were measured during maximally rapid opening and closing tasks, and during increasingly rapid repetitions of a spoken syllable and a nonspeech "syllable." The results indicate that (1) peak acceleration levels for the repeated mandible movements were less than half of those for the maximally rapid single mandible movements, and (2) a rather different mode of control is used for the repeated speech movements as compared to the nonspeech movements.

Humans↗
PubMed1983

Enlargement of the supraglottal cavity and its relation to stop consonant voicing.

Measurements were made of saggital plane movements of the larynx, soft palate, and portions of the tongue, from a high-speed cinefluorographic film of utterances produced by one adult male speaker of American English. These measures were then used to approximate the temporal variations in supraglottal cavity volume during the closures of voiced and voiceless stop consonants. All data were subsequently related to a synchronous acoustic recording of the utterances. Instances of /p,t,k/ were always accompanied by silent closures, and sometimes accompanied by decreases in supraglottal volume. In contrast, instances of /b,d,g/ were always accompanied both by significant intervals of vocal fold vibration during closure, and relatively large increases in supraglottal volume. However, the magnitudes of volume increments during the voiced stops, and the means by which those increments were achieved, differed considerably across place of articulation and phonetic environment. These results are discussed in the context of a well-known model of the breath-stream control mechanism, and their relevance for a general theory of speech motor control is considered.

Cineradiography↗
PubMed1981

The effects of antagonistic gestures on temporal and amplitude parameters of anticipatory labial coarticulation.

Anticipatory lip rounding before neutral versus antagonistic vowel environments was studied in a test of the compatibility notion of a look-ahead scanning mechanism (Henke, 1967). Electromyograms were obtained from orbicularis oris superior, an agonist for lip rounding, and risorius, an agonist for lip spreading, from three normal speakers repeating the nonsense disyllables /tiku/, /taku/, /tuki/, /kikstu/, and /kakstu/ twenty times each. When the syllable-initial vowel was the lip spread vowel /i/, oris activity began earlier and with greater force than for syllable-initial /a/ contexts across all speakers. This finding argues for a revision of a key assumption underlying the look-ahead scan model for anticipatory lip rounding. The encoding program for speech exhibits temporal and amplitude adjustments in its coarticulatory behavior to accommodate in an active way contradictory neuromuscular and biomechanical conditions. These results are discussed with reference to current models of speech production.

Adult↗
PubMed1979

Mechanical properties of single motor units in speech musculature.

Electromyograms were recorded from three subjects during steady, low-rate discharge of single motor units of anterior belly of digastric, accompanying maintenance of isometric tension. The overall tension developed in muscles subserving mandibular depression was recorded from a force tansducer situated inferior to the mandibular symphysis. The force transducer output from the 90 ms period immediately following each of the several hundred discharges of a motor unit was averaged to obtain a characteristic tension curve for the contractile response (twitch) of that unit. Peak twitch tensions and time taken to develop peak tension (contraction time) were recorded for 27 motor units. The obtained median twitch tension of 0.26 g and contraction time of 29 ms were compared with values obtained for units in other human muscles and in animal muscles. As expected from the size principle, later recruited units possessed higher twitch tensions. Contrary to some statements of the size principle, contraction times were not shorter in later recruited units. Data on muscles elevating the mandible were also evaluated.

Adult↗
PubMed1978

A laterality effect in isometric and isotonic labial tracking.

Hemispheric dominance for sensorimotor control of lip activity was investigated by use of a pursuit auditory tracking task. This task involves continuous frequency matching of a computer-generated target tone and a subject-controlled cursor tone. Thirty right-handed subjects were tested under isometric lip and hand control, and 20 right-handed subjects under isotonic lip control. Subjects tracked 10 1-min trials under each laterality condition--cursor/right ear, target/left ear, and vice versa. In both experiments tracking performance was better when the lip-controlled cursor tone was presented to the right ear (hence direct contralateral route to left hemisphere). A significant (p less than 0.05) cursor/right-ear advantage was found under isometric hand-tracking. Analysis routines examined relative laterality advantages across several time intervals within each 1-min trial. Consistent lateralization scores in favor of cursor/right-ear presentations (REAs) were independent of the time interval measured. For isometric tracking, 58% of subjects having laterality advantages (p less than 0.10) revealed REAs. For isotonic tracking, 71% of subjects revealed REAs. Implications of the latter finding are discussed relative to a left hemisphere mechanism specialized to integrate movement-generated auditory feedback with dynamic kinesthetic information from the articulators.

Adolescent↗
PubMedDate not supplied

Kinematic event patterns in speech: special problems.

The view that each utterance is fundamentally a pattern of serially-ordered events underlies a group of well-known speech kinematic studies emphasizing temporal coordination among articulators. Methodological problems that might affect the validity and significance of conclusions from these studies are identified. Results from a new analysis of synchronous acoustic and fleshpoint-kinematic data, recorded from 53 normal young-adult speakers of American English, are then reported. The kinematic data represented speech-related actions of the tongue blade and dorsum, both lips, and the mandible, during the test words special and problem, and were drawn from an existing X-ray microbeam speech production database. Distributions of event patterns across speakers revealed four main results: (1) different patterns for the two test words; (2) a comparable degree of cross-speaker agreement about relative tongue and jaw movement timing, but marked disagreement about lip and jaw movement timing, between test words; (3) highly distinctive movement patterns for some speakers; and, (4) a general conclusion that serial event order, alone, provides very limited understanding of movement patterns produced by individual speakers. By design, these results focus attention on methods of kinematic event pattern analyses, and the general value of such analyses for insights about speech production.

Adolescent↗