Gary Weismer

Acoustic and intelligibility characteristics of sentence production in neurogenic speech disorders.

The purpose of this study was to examine the relationship between scaled speech intelligibility and selected acoustic variables in persons with dysarthria. Control speakers and speakers with amyotrophic lateral sclerosis (ALS) and Parkinson’s disease (PD) produced sentences which were analyzed acoustically and perceptually. The acoustic variables included total utterance durations, segment durations, estimates of the acoustic vowel space, and slopes of formant transitions; the perceptual variables included scaled speech intelligibility and severity of speech involvement. Results indicated that the temporal variables typically differentiated the ALS group, but not the PD group, from the controls, and that vowel spaces were smaller for both neurogenic groups as compared to controls, but only significantly so for the ALS speakers. The relation of these acoustic measures to scaled speech intelligibility is shown to be complex, and the composite results are discussed in terms of sentence vs. single-word intelligibility estimates and their underlying acoustic bases.

Kinematic, acoustic, and perceptual analyses of connected speech produced by Parkinsonian and normal geriatric adults

Acoustic and kinematic analyses, as well as perceptual evaluation, were conducted on the speech of Parkinsonian and normal geriatric adults. As a group, the Parkinsonian speakers had very limited jaw movement compared to the normal geriatrics. For opening gestures, jaw displacements and velocities produced by the Parkinsonian subjects were about half those produced by the normal geriatrics. Lower lip movement amplitude and velocity also were reduced for the Parkinsonian speakers relative to the normal geriatrics, but the magnitude of the reduction was not as great as that seen in the jaw. Lower lip closing velocities expressed as a function of movement amplitude were greater for the Parkinsonian speakers than for the normal geriatrics. This increased velocity of lower lip movement may reflect a difference in the control of lip elevation for the Parkinsonian speakers, an effect that increased with the severity of dysarthria. Acoustically, the Parkinsonian subjects had reduced durations of vocalic segments, reduced formant transitions, and increased voice onset time compared to the normal geriatrics. These effects were greater for the more severe, compared to the milder, dysarthrics and were most apparent in the more complex, vocalic gestures.

Acoustic studies of dysarthric speech: Methods, progress, and potential

EDUCATIONAL OBJECTIVES (1) The reader will be able to describe the major types of acoustic analysis available for the study of speech, (2) specify the components needed for a modern speech analysis laboratory, including equipment for recording and analysis, and (3) list possible measurements for various aspects of phonation, articulation and resonance, as they might be manifest in neurologically disordered speech.

Philosophy of research in motor speech disorders

The primary objective of this position paper is to assess the theoretical and empirical support that exists for the Mayo Clinic view of motor speech disorders in general, and for oromotor, nonverbal tasks as a window to speech production processes in particular. Literature both in support of and against the Mayo clinic view and the associated use of oromotor, nonverbal tasks, is reviewed, along with literature from normal speech production and neurophysiology. This literature is organized and analysed to show that theoretical and experimental support for the Mayo view is weak at best, and that the frequent appeal to oromotor, nonverbal tasks is misguided. We conclude that studies of speech production in motor speech disorders, rather than oromotor nonverbal control or of neurological signs, is the correct approach for advancing the field.

Relationships between speech intelligibility and the slope of second-formant transitions in dysarthric subjects

The relationship between speech intelligibility on a single-word identification test and the average second-formant (F2) slope of selected test words was examined for a group of 25 men and ten women with amyotrophic lateral sclerosis (ALS). A Spearman rank-order correlation coefficient greater than 0.80 was obtained for both the male and female subjects. This moderately high correlation indicates that the F2 slope index is a useful acoustic measure of speech proficiency in ALS. F2 slope indices are reported for normal control populations of geriatric men and women. In addition, progressive deterioration of the F2 slope index is illustrated in a case study of one woman with ALS.

Formant trajectory characteristics of males with amyotrophic lateral sclerosis

The purpose of this study was to describe the formant trajectories produced by males with amyotrophic lateral sclerosis (ALS), a degenerative neuromuscular disease that is typically associated with dysarthria. Formant trajectories of 25 males with ALS and 15 neurologically normal geriatric males were compared for 12 words selected from the speech intelligibility task developed by Kent et al. [J. Speech. Hear. Disord. 54, 482-499 (1989)]. The results indicated that speakers with ALS (1) produced formant transitions having shallower slopes than transitions of normal speakers, (2) tended to produce exaggerations of formant trajectories at the onset of vocalic nuclei, and (3) had greater interspeaker variability of formant transition characteristics than normal speakers. Within the group of ALS speakers, those subjects who were less than 70% intelligible produced distinctly more aberrant trajectory characteristics than subjects who were more than 70% intelligible. ALS subjects who were less than 70% intelligible produced many trajectories that were essentially flat, or that had very shallow slopes. These results are discussed in terms of the speech production deficit in the dysarthria associated with ALS, and with respect to the potential influence of aberrant trajectories on speech intelligibility.

A speaking task analysis of the dysarthria in cerebellar disease.

Cerebellar disease affects a number of skilled movements, including those in speech. Ataxic dysarthria, the speech disorder that typically accompanies cerebellar disease, was studied by acoustic methods. Control subjects and subjects with ataxic dysarthria were recorded while performing a number of speaking tasks, including sustained vowel phonation, syllable repetition, monosyllabic word production (intelligibility test), sentence recitation, and conversation. Acoustic data derived from the speech samples confirmed the hypothesis that temporal dysregulation is a primary component of the speech disorder. The data also show that the nature of the disorder varies with the speaking task. This result agrees with observations on other motor systems in subjects with cerebellar disease and may be evidence of a dissociation of impairments. Suggestions are offered on the selection of measures for a given task and on the role of the cerebellum in the regulation of speaking.

Statistical analysis of word-initial /k/ and /t/ produced by normal and phonologically disordered children

The acoustic characteristics of voiceless velar and alveolar stop consonants were investigated for normally articulating and phonologically disordered children using spectral moments. All the disordered children were perceived to produce /t/ for /k/, with /k/ being absent from their phonetic inventories. Approximately 82% of the normally articulating childrens consonants were classified correctly by discriminant function analysis, on the basis of the mean (first moment), skewness (third moment) and kurtosis (fourth moment) derived from the first 40 ms of the VOT interval. When the discriminant function developed for the normally articulating children was applied to the speech of the phonologically disordered group of children, no distinction was made between the velar and alveolar stops. Application of the model to the speech of individual children in the disordered group revealed that one child produced distinct markings to the velar-alveolar contrast. Variability measures of target /t/ and /k/ utteranc...

Effect of speaking rate manipulations on acoustic and perceptual aspects of the dysarthria in amyotrophic lateral sclerosis

The current study explored the acoustic and perceptual effects of speaking rate adjustments in persons with amyotrophic lateral sclerosis (ALS) and in neurologically normal individuals. Sentence utterances were obtained from the participants at two self-selected speaking rates: habitual and fast. Total utterance durations, segment durations, and vowel formant frequencies comprised the acoustic measures, whereas magnitude estimates of speech intelligibility and severity of speech involvement were the perceptual measures. Results showed that participants in both the neurologically normal and ALS groups were able to increase their speaking rate when asked to do so, but that the participants with ALS were significantly slower than the neurologically normal participants at both rates. Both groups of participants also showed compression of the acoustic vowel space with increased speaking rate, with the vowel spaces of participants with ALS generally being more compressed than the vowel spaces of neurologically normal participants, at either rate. Most importantly, the perceptual measures failed to show any effect of the speaking rate adjustment on scaled intelligibility or severity, for either group. These findings are discussed relative to the general issue of slow habitual speaking rates among many speakers with dysarthria, and possible explanations for the slowness. The lack of an effect of increased rate on the perception of the speech deficit among speakers with ALS argues against the idea that the habitually slow rates are a form of compensation to reduce the complexity of speech production.

What dysarthrias can tell us about the neural control of speech

Abstract Dysarthrias, part of the class of neurogenic speech disorders, provide several sources of evidence concerning the neural control of speech. Although the dysarthrias have been studied primarily from a clinical perspective directed to issues of assessment and management, they have much to tell us about how the brain regulates the act of speaking. This paper considers five major areas in which disordered and normal speech can be integrated into an improved understanding of speech motor control: sensory function in the regulation of speech; rhythm as a temporal substrate for the organization of speech movements; kinematics of individual movements and motor systems; neural bases of multi-articulator coordination; and strategies for compensation, adaptation, and re-organization. A theme that runs through these five areas is consideration of the overarching hypothesis that speech motor regulation is based on a modular organization that can be defined partly by consideration of results from neurogenic speech disorders.