The present investigation was designed to elucidate the potential influence of age on speech breathing. Toward this end, 30 men representing three widely different age groups (25, 50, and 75 years) were studied. These individuals were carefully selected to meet stringent criteria, the most important of which related to health and physical characteristics. Speech breathing was studied via anteroposterior diameter changes of the rib cage and abdomen. Recordings were made during extemporaneous speaking and reading and during the performance of various chest wall maneuvers used in the measurement of the speech breathing data. In addition to speech breathing, selected measures of general respiratory function were obtained. These included measures of subdivisions of the lung volume and measures of resting tidal breathing. Results indicated that these 30 subjects were representative of other subjects studied with respect to measures of general respiratory function. Subdivisions of the lung volume were found to differ with age in the manner predicted by previous investigations. Age-related differences were most marked for measures of vital capacity and residual volume. By contrast, there were no age-related differences for measures of resting tidal breathing. Several speech breathing measures were found to differ with age. Age-related differences were usually between the 25- and 75-year-old subject groups and less commonly between the 25- and 50-year-old subject groups. For extemporaneous speaking, differences were found for lung volume excursion, rib cage volume initiation (referenced to the rib cage volume associated with the relaxed configuration of the chest wall), number of syllables per breath group, and lung volume expended per syllable (in percent vital capacity). For reading, differences were found for lung volume expended per syllable (in percent vital capacity). Age-related similarities and differences in general respiratory function and speech breathing are discussed in relation to possible underlying mechanisms. In addition, implications are drawn regarding evaluation and management of individuals with speech breathing disorders.

This thesis was concerned with coarticulatory patterns across various speech articulators and whether these can be accounted for by similar movement organization principles. Movements of the tongue dorsum, and the upper and lower pharynx, were recorded separately by a computerized ultrasound system during the production of vowel-consonant-vowel sequences. The movement amplitude, duration, and onset (relative to specific acoustic events) were computed for each articulator for a variety of speech gestures. It was shown that both spatial and temporal aspects of the movements varied in a similar manner for the three articulators as a function of the phonological context. The results indicate that spatiotemporal articulatory adjustments for vowels co-occur with the articulation of a consonant. This pattern can be accounted for by the notions of co-production and the 'spatial proximity' hypothesis.

This thesis explores the coarticulatory effects of English /l/ and /r/, examining their articulatory basis, acoustic manifestation and perceptual relevance. It demonstrates that there are perceptually relevant coarticulatory differences associated with the distinction between /l/ and /r/. Two perceptual experiments, an articulatory experiment and a modelling study were conducted. Both perceptual experiments used a modified gating technique. The first experiment demonstrates that the coarticulatory effects of /l/ and /r/ on surrounding vowels and consonants can sometimes be used by listeners to identify an HI or /r/ which has been deleted and replaced by noise. The second perceptual experiment shows that the cues for an /r/ are more perceptually salient than those for an /l/. The articulatory experiment used simultaneous electromagnetic articulography, electropalatography and acoustic recordings to investigate the coarticulatory effects of /l/ and /r/. In /r/ contexts, relative to /l/ contexts, raising and retraction of the tongue, lip rounding and lowering of F₃ were found, up to two syllables preceding and following the /r/. The extent of this coarticulatory effect is far greater than commonly acknowledged in the coarticulation literature. Phonetic and phonological theories fail to predict or account for effects of this extent. The theory that coarticulation can be modelled as overlap of articulatory gestures was tested in a modelling study. A subset of the articulatory data was modelled numerically using dynamical descriptions of articulatory gestures from an approach developed at Haskins Laboratories. The modelling showed that longdistance coarticulatory effects could not be adequately accounted for by gestural overlap alone. Feature-spreading models, such as Keating's window model of coarticulation, are also unable to account for these effects adequately. The results of this thesis pose a challenge to current phonetic and phonological theory, as they show that coarticulatory effects have greater extent than commonly recognised.

A series of experiments are described which explore the relationship between biomechanical properties and the control of jaw movement in speech. This relationship is documented using kinematic analyses in conjunction with a mathematical model of jaw motion and direct measures of jaw stiffness. / In the first experiment, empirical and modeling studies were carried out to examine whether the nervous system compensates for naturally occurring forces acting on the jaw during speech. As subjects walk or run, loads to the jaw vary with the direction and magnitude of head acceleration. While these loads are large enough to produce a measurable effect on jaw kinematics, variation in jaw position during locomotion is shown to be substantially reduced when locomotion is combined with speech. This reduction in jaw motion is consistent with the idea that in speech, the control of jaw movement is adjusted to offset the effects of head acceleration. Results of simulation studies using a physiologically realistic model of the jaw provide further evidence that subjects compensate for the effects of self-generated loads by adjusting neural control signals. / A second experiment explores the idea that a principle mechanical property of the jaw---its spring-like behavior, or stiffness---might influence patterns of kinematic variation in speech movements. A robotic device was used to deliver mechanical perturbations to the jaw in order to quantify stiffness in the mid-sagittal plane. The observed stiffness patterns were non-uniform, with higher stiffness in the protrusion-retraction direction. Consistent with the idea that kinematic patterns reflect directional asymmetries in stiffness, a detailed relationship between jaw kinematic variability and stiffness was observed---kinematic variability was consistently higher under conditions in which jaw stiffness was low. Modeling studies suggested that the pattern of jaw stiffness is significantly determined by jaw geometrical properties and muscle force generating abilities. / A third experiment examines the extent to which subjects are able to alter the three-dimensional pattern of jaw stiffness in a task-dependent manner. Destabilizing loads were applied to the jaw in order to disrupt the ability of subjects to maintain a static jaw posture. Subjects adapted by increasing jaw stiffness in a manner that depended on the magnitude and, to a more limited extent, direction of the destabilizing load. The results support the idea that stiffness properties can be controlled in the jaw, and thus may play a role in regulating mechanical interactions in the orofacial system.

External loads, such as those due to the orientation of body segments relative to gravity, affect the extent to which control signals result in the achievement of desired goals. The degree to which subjects adjust control signals to compensate for loads provides a measure of what the nervous system knows about forces affecting motion and gives an indication of the complexity of control signals needed for voluntary movement. In the present study, we have explored the hypothesis that subjects take no account of the orientation of the head relative to gravity when making jaw movements during speech. We used a simulation model of the jaw to predict the kinematic effect of using a single set of motor commands (which take no account of the relative direction of the gravitational force) to produce speech-like movements while the body was in three different orientations: upright, prone and supine. The simulations predict a systematic change in jaw pitch angle and horizontal translation resulting from the change in body orientation. Empirical results for five subjects tested under the same conditions as those explored in the simulations are for the most part consistent with the pattern predicted by the model. This suggests that in the case of jaw movements during speech, control signals are not adjusted to account for changes in head and body orientation relative to gravity.

In the clinical evaluation and management of speech disorders, a speech-language pathologist may observe disturbances in a client's motor abilities that suggest possible neurological dysfunction. One possible disturbance is in oral diadochokinesis (DIO), an individual's ability to start and stop the movement of the articulators rapidly and execute repetitive, alternating, sequential movements typically associated with speech articulation. It is often recommended that a speech-language pathologist test DIO speed and compare the performance to available norms. There is, however, a lack of normative DIO data spanning all ages of adulthood. The purpose of this study was to develop preliminary normative data on the speed of oral diadochokinesis used in articulation of syllables and oral movements by adults. The investigation sought to answer the question: What are the mean rates of oral diadochokinetic syllable productions and selected oral movements for each decade of adulthood?

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