Biomedical subjects

John R Westbury

Publications and source records attributed to John R Westbury.

4 recordsLinked to original sources

PubMed2003

Interarticulator coordination in dysarthria: an X-ray microbeam study.

Articulatory discoordination is often said to be an important feature of the speech production disorder in dysarthria, but little experimental work has been done to identify and specify the coordination difficulties. The present study evaluated the coordination of labial and lingual gestures for /u/ production in persons with Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and in control participants. Both tongue backing/raising and reduction of the area enclosed by the lips can produce the characteristic low F2 of /u/. The timing of these articulatory gestures with respect to the acoustic target of a low F2 was inferred from X-ray microbeam data. Pellet motions of the tongue dorsum and lips revealed the timing of the lingual and labial gestures to be strongly linked together (synchronized), predictive of the temporal location of the lowest F2 within the vocalic nucleus, and scaled proportionately to the overall vowel duration in control participants. Somewhat surprisingly, essentially the same findings were obtained in the speakers with dysarthria. These relationships were noisier among the speakers with dysarthria, but the global synchronization patterns applied to all 3 groups. Further analyses revealed the synchronization to be less well defined and more variable across speakers with ALS, as compared to speakers with PD and the controls. Results are discussed relative to concepts of coordination in dysarthria.

Adult↗

PubMed2002

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.

Adult↗

PubMed2002

Defining and measuring speech movement events.

A long-held view in speech research is that utterances are built up from a series of discrete units joined together. However, it is difficult to reconcile this view with the observation that speech movement waveforms are smooth and continuous. Developing methods for reliable identification of speech movement units is necessary for describing speech motor behavior and for addressing theoretically relevant questions about its organization. We describe a simple method of parsing movement signals into a series of individual movement "strokes," where a stroke is defined as the period between two successive local minima in the speed history of an articulator point, and use that method to segment speech-related movement of marker points placed on the tongue blade, tongue dorsum, lower lip, and jaw in a group of healthy young speakers. Articulator fleshpoints could be distinguished on the basis of kinematic features (i.e., peak and boundary speed, duration and distance) of the strokes they produce. Further, tongue blade and jaw fleshpoint strokes identified to temporally overlap with acoustic events identified as alveolar fricatives could be distinguished from speech strokes in general on the basis of a number of kinematic measures. Finally, the acoustic timing of alveolar fricatives did not appear to be related to the kinematic features of strokes presumed to be related to their production in any direct way. The advantages and disadvantages of this simple approach to defining movement units are discussed.

Adult↗

PubMed2002

Tongues and lips without jaws: a comparison of methods for decoupling speech movements.

Speech-related motions of small markers attached to the tongue, lower lip, and lower jaw of 44 normal young adult talkers of American English were analyzed to estimate the relative accuracy of selected methods for decoupling tongue and lip motions from ongoing jaw motion when all movements are originally measured relative to a common reference frame (such as the head). In general, results of the analysis show that a common "simple subtraction" method that ignores pitching rotation of the jaw yields larger errors in positions and speeds of decoupled tongue and lip markers than methods that do not ignore rotation. When the jaw is widely opened, is moving quickly, and/or when any decoupled marker is relatively far from the origin of a local coordinate system fixed to the jaw, positional and speed errors associated with the subtraction method can exceed 5 mm and 25 mm/s, respectively. We propose a simple procedure for estimating the pitching rotation of the jaw that can be applied when pitch cannot be measured. We then show that decoupled motions of tongue and lower lip markers based on estimated jaw rotation involve less error than those derived from any other decoupling method considered. Careful attention to processing methods should yield more accurate inferences about the nature and degree of coordination between speech-related movements of the tongue and lower lip that are decoupled from, and hence independent of, concurrent movements of the lower jaw.

Adult↗