John R. Westbury

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.

Differences among speakers in lingual articulation for American English /ɹ/

Abstract X-ray microbeam fleshpoint measures of lingual articulation for pre-vocalic /ɹ/ were obtained for five test words spoken by 53 normal, young adult talkers of American English. The data were used to develop quantitative descriptions of cross-speaker variation in tongue shapes at acoustically-defined r-moments in the test words, and to understand whether and how /ɹ/-related tongue shapes might vary across the available sample of phonetic contexts. Key results suggest that tongue shapes for this sound vary widely across speakers within any single phonetic context, and more continuously than categorically across the representational space. Shapes also vary by context in ways that are similar across most speakers, and in some contexts, in ways that can be expected given simple assumptions about lingual movements associated with adjacent sounds. Interestingly, tongue shapes for American English /ɹ/ do not seem to be reliably linked to gender, measures of oral cavity size, or formant frequencies measured for two of the test words. Together, these results provide unique insight about the nature and bases of inter-speaker variation in lingual articulation for this infamously variable sound, and may prove useful to other investigators interested in speech motor control, speech synthesis, and automatic speech recognition.

On coordinate systems and the representation of articulatory movements

Hypothetical examples are used to demonstrate how certain quantitative characterizations of kinematic events can be affected by the placement and orientation of reference axes against which measurements are made. The variation in coordinate systems among a representative sample of recent publications describing speech movements and postures is summarized, and a standard, easily defined coordinate system for future descriptions is proposed. Interpretative benefits associated with the proposed representational standard are noted.

Variability in tongue movement kinematics during normal liquid swallowing.

This study sought to develop a quantitative kinematic description of tongue movement for liquid swallowing in a group of 12 healthy subjects. X-ray microbeam technology was used to track the positions of six small pellets attached to the tongue and jaw while subjects swallowed water at 2- and 10-mL bolus volumes. A feature common to all subjects was a prominent rostral movement of the dorsal region of the tongue. In addition, all subjects consistently increased the displacement and maximum speed of this tongue movement with increased bolus volume. However, detailed movement analysis showed a variety of tongue movement patterns for the group. This variability across subjects was large enough that it was surprisingly difficult to provide a low-dimension quantitative description of the tongue kinematics during liquid swallowing.

Speed–curvature relations for speech-related articulatory movement

Abstract During speech production, oral articulator points exhibit spatially complex trajectories. This spatial complexity is partially reflected in the trajectorys curvature history (where curvature is defined as the rate of change of direction, parameterized for arc length). Informal observation of articulatory movement reveals that an increase in the degree of trajectory curvature is often associated with a slowing of the articulator. Such a relation between the speed and curvature of movement has been quantified for a variety of behaviors within the limb and oculomotor systems. This relation has been called the 1/3 power law. Such an association has not been quantified for speech movements. If speech movements adhere to the 1/3 power law, it would imply a specific constraint on the variability in spatial complexity (as reflected by curvature) and the time course of speech-related movements. This study empirically evaluated the relationship between articulator speed and trajectory curvature for speech-related mid-sagittal planar movements of the tongue, lower lip and mandible in a group of healthy speakers. Results revealed that movement speed and trajectory curvature are related by a power function whose exponent is near, but not exactly 1/3. Articulators exhibited systematic variations in the strength of association, and value of the exponent. These results suggest that speed and curvature of speech movement covary in ways similar to other motor systems.

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%.

X‐ray microbeam speech production database

A broad review of literature describing lingual function during speech shows that speaker samples per study are typically small (N<3 in more than 80% of all cases), and that speech samples, and representational and analysis conventions are highly variable. Similar conclusions can be drawn for other articulators. Thus it is fair to argue that there is still not available any valid, statistically‐defensible sense of normal speech motor behavior, against which disordered articulatory behavior can be compared. Accordingly, a large‐sample, 50‐speaker x‐ray microbeam speech database will be developed at the University of Wisconsin, incorporating point‐parametrized representations of lingual, labial, mandibular, and velar movements in association with the resulting acoustic sound pressure wave, for a rich set of utterances and oral motor tasks, and lengthy recording interval (circa 18 min/speaker). The database is intended to be uniform across speakers in task inventory and descriptive kinematic framework; suffi...

Time-varying acoustic and articulatory characteristics of American English [ɹ]: a cross-speaker study

Abstract The present study is an attempt to discover time-varying acoustic correlates of articulatory movements of American English [ɹ] using the X-ray microbeam speech production database. American English [ɹ] is known to be variable in its articulatory postures, whereas a single acoustic correlate—a low third formant—is associated with the sound. A previous study (Westbury, Hashi, & Lindstrom (1998), Speech Communication 26, 203–226) found no relation between articulatory postures and formant frequencies at phonation onset of words beginning with the sound. The present study examined acoustic–articulatory relations in time-varying acoustic and articulatory characteristics in the transition from [ɹ] to a following low- or mid-back vowel. In intervals involving a major F3 rise, a relatively strong correlation (r⩾0.7) was observed between the average rate of change in F3 (F3 slope) and the speed of the tongue pellet closest to the palate at the onset of the major F3 rise. Results from the study are discussed with respect to the acoustic theory of speech production.

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 fleshpointkinematic 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.

An articulatory characterization of contrastive emphasis in correcting answers

New recordings of articulatory movements of the tongue, lips, and mandible have been obtained using the University of Wisconsin x‐ray microbeam system, from eight normal adult speakers of American English who uttered three‐number sequences in question‐answer pairs such as “Is it 995 Pine Street? No, its 955 Pine Street.” Analysis of these data is intended to provide a detailed characterization of the implementation of contrastive emphasis observed in this context. Preliminary comparisons of maximum displacements and peak velocities for the tongue blade and lower lip, during the words “nine” and “five,” respectively, show that both movement parameters increase during a syllable under the influence of contrastive emphasis, but that the relative change in articulator displacement is always greater. This observation is at least partly consistent with results of previous research [Fujimura and Spencer, J. Acoust. Soc. Am. Suppl. 1 74, S117 (1983)], which showed that maximum articulator displacements during em...