Segmental level analysis of laryngeal function in persons with motor speech disorders.

Laryngeal behavior for segmental function is often disturbed in motor speech disorders. Loss of voicing contrasts has been shown to significantly contribute to speech intelligibility deficits. The present study was designed to examine two commonly erred laryngeal contrasts, the word-initial voiced-voiceless and glottal-null contrasts using acoustic analysis techniques. Acoustic measures were compared to expectations for the contrast based on data in the literature as well as listeners' perception of the token. Findings indicate a mismatch between acoustic data and both expectations for the contrasts and listener perception. There is some indication that changes in laryngeal segmental function are related to aging in general and may be exaggerated in persons with motor speech disorders.

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.

The relationship between perception and acoustics for a high-low vowel contrast produced by speakers with dysarthria.

This study was designed to explore the relationship between perception of a high-low vowel contrast and its acoustic correlates in tokens produced by persons with motor speech disorders. An intelligibility test designed by Kent, Weismer, Kent, and Rosenbek (1989a) groups target and error words in minimal-pair contrasts. This format allows for construction of phonetic error profiles based on listener responses, thus allowing for a direct comparison of the acoustic characteristics of vowels perceived as the intended target with those heard as something other than the target. The high-low vowel contrast was found to be a consistent error across clinical groups and therefore was selected for acoustic analysis. The contrast was expected to have well-defined acoustic measures or correlates, derived from the literature, that directly relate to a listeners' responses for that token. These measures include the difference between the second and first formant frequency (F2-F1), the difference between F1 and the fundamental frequency (FO), and vowel duration. Results showed that the acoustic characteristics of tongue-height errors were not clearly differentiated from the acoustic characteristics of targets. Rather, the acoustic characteristics of errors often looked like noisy (nonprototypical) versions of the targets. Results are discussed in terms of the test from which the errors were derived and within the framework of speech perception theory.

Ataxic dysarthria.

Although ataxic dysarthria has been studied with various methods in several languages, questions remain concerning which features of the disorder are most consistent, which speaking tasks are most sensitive to the disorder, and whether the different speech production subsystems are uniformly affected. Perceptual and acoustic data were obtained from 14 individuals (seven men, seven women) with ataxic dysarthria for several speaking tasks, including sustained vowel phonation, syllable repetition, sentence recitation, and conversation. Multidimensional acoustic analyses of sustained vowel phonation showed that the largest and most frequent abnormality for both men and women was a long-term variability of fundamental frequency. Other measures with a high frequency of abnormality were shimmer and peak amplitude variation (for both sexes) and jitter (for women). Syllable alternating motion rate (AMR) was typically slow and irregular in its temporal pattern. In addition, the energy maxima and minima often were highly variable across repeated syllables, and this variability is thought to reflect poorly coordinated respiratory function and inadequate articulatory/voicing control. Syllable rates tended to be slower for sentence recitation and conversation than for AMR, but the three rates were highly similar. Formant-frequency ranges during sentence production were essentially normal, showing that articulatory hypometria is not a pervasive problem. Conversational samples varied considerably across subjects in intelligibility and number of words/ morphemes in a breath group. Qualitative analyses of unintelligible episodes in conversation showed that these samples generally had a fairly well-defined syllable pattern but subjects differed in the degree to which the acoustic contrasts typical of consonant and vowel sequences were maintained. For some individuals, an intelligibility deficit occurred in the face of highly distinctive (and contrastive) acoustic patterns.

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.

The effects of a flattened fundamental frequency on intelligibility at the sentence level.

The purpose of this preliminary experiment was to evaluate the effect of a flattened fundamental frequency (F0) contour on sentence intelligibility. The perceptual dimension monotone pitch is frequently used to describe the speech of persons with dysarthria, and relatively flat F0 contours have been noted in several acoustic studies of dysarthria. To determine the independent effect of a flattened F0 contour on sentence intelligibility a resynthesis technique was used that held timing and spectral characteristics of utterances constant while allowing parametric control over successive pitch periods. Two male speakers produced low-probability utterances selected from the SPIN test, which were then resynthesized with a flattened F0 contour. Speech intelligibility was assessed using two measures: one involving word transcription and the other interval scaling. These measures were collected from 10 listeners. The results showed that both measures were significantly lower when the F0 contour was flattened, as compared with naturally varying contours. Several different explanations are proposed for this effect, which can and should be explored in greater detail using the resynthesis technique given the prominence of this characteristic in dysarthria.

Acoustic characteristics of /s/ in adolescents.

The goal of the current study was to construct a reference database against which misarticulations of /s/ can be compared. Acoustic data for 26 typically speaking 9- to 15-year-olds were examined to resolve measurement issues in acoustic analyses, including alternative sampling points within the /s/ frication; the informativeness of linear versus Bark transformations of each of the 4 spectral moments of /s/ (Forrest, Weismer, Milenkovic, & Dougall, 1988); and measurement effects associated with linguistic context, age, and sex. Analysis of the reference data set indicates that acoustic characterization of /s/ is appropriately and optimally (a) obtained from the midpoint of /s/, (b) represented in linear scale, (c) reflected in summary statistics for the 1 st and 3rd spectral moments, (d) referenced to individual linguistic-phonetic contexts, (e) collapsed across the age range studied, and (f) described individually by sex.

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.

Influences of pellet markers on speech production behavior: acoustical and perceptual measures.

Peri- and intraoral devices are often used to obtain measurements concerning articulator motions and placements. Surprisingly, there are few formal evaluations of the potential influence of these devices on speech production behavior. In particular, the potential effects of lingual pellets or coils used in x-ray or electromagnetic studies of tongue motion have never been evaluated formally, even though a large x-ray database exists and electromagnetic systems are commercially available. The x-ray microbeam database [Westbury, J. "X-ray Microbeam Speech Production Database User's Handbook, version 1" (1994)] includes several utterances produced with pellets-off and -on, which allowed us to evaluate effects of pellets for the utterance, She had your dark suit in greasy wash water all year, using acoustic and perceptual measures. Overall, there were no acoustic or perceptual measures that showed consistent effects of pellets across speakers, but certain effects were consistent either within a given speaker or in direction across a subgroup of the speakers. The results are discussed in terms of the general goodness of the assumption that point parameterization of lingual motion does not interfere with normal articulatory behaviors. A brief screening procedure is suggested to protect articulatory kinematic experiments from those individuals who may show consistent effects of having devices placed on perioral structures.

Speaking-rate-induced variability in F2 trajectories.

This study examined speaking-rate-induced spectral and temporal variability of F2 formant trajectories for target words produced in a carrier phrase at speaking rates ranging from fast to slow. F2 onset frequency measured at the first glottal pulse following the stop consonant release in target words was used to quantify the extent to which adjacent consonantal and vocalic gestures overlapped; F2 target frequency was operationally defined as the first occurrence of a frequency minimum or maximum following F2 onset frequency. Regression analyses indicated 70% of functions relating F2 onset and vowel duration were statistically significant. The strength of the effect was variable, however, and the direction of significant functions often differed from that predicted by a simple model of overlapping, sliding gestures. Results of a partial correlation analysis examining interrelationships among F2 onset, F2 target frequency, and vowel duration across the speaking rate range indicated that covariation of F2 target with vowel duration may obscure the relationship between F2 onset and vowel duration across rate. The results further suggested that a sliding based model of acoustic variability associated with speaking rate change only partially accounts for the present data, and that such a view accounts for some speakers' data better than others.

Interspeaker variation in habitual speaking rate: evidence for a neuromuscular component.

Neuromuscular and sociolinguistic hypotheses were proposed to explore and account for the nature of individuals' idiosyncratic speech rates. One hundred subjects (50 males and 50 females) read the Farm Script passage at both habitual and maximum rates. FAST and SLOW subgroups of subjects were selected for both genders based on their overall speaking rates. The articulation rate data derived from 30 selected subjects (SLOW and FAST) revealed the following findings: (a) a significant linear regression function existed between the habitual and maximum rates, (b) significantly different maximum rates were found for the SLOW and the FAST groups, (c) roughly equivalent relative changes from habitual to maximum rate for both SLOW and FAST groups. No significant gender differences were found across different speech tasks and measures of speech rates. The weight of the evidence seems to suggest that neuromuscular constraints play a role in the determination of an individual's habitual speaking rate. Nevertheless, the study did not suggest that either neuromuscular hypotheses or sociolinguistic hypotheses alone can account for the control of individuals' speaking rates due to the unusual ability demonstrated by a few subjects in the SLOW group, to speak at very fast maximum rates.

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.

The influence of speaking rate on vowel space and speech intelligibility for individuals with amyotrophic lateral sclerosis.

The relationship between speaking rate, vowel space area, and speech intelligibility was studied in a group of 9 subjects with amyotrophic lateral sclerosis (ALS) and 9 age- and gender-matched controls. Subjects read a standard passage (the Farm Passage) at three speaking rates, including HABITUAL, FAST, and SLOW. Vowel segment durations and target formant frequencies were measured at each speaking rate from select words containing the vowels /i/, /ae/, /a/, and /u/. To quantify changes in vowel space area across speaking rate, the area of the vowel quadrilateral was calculated for each speaker at each speaking rate. In addition, intelligibility estimates at each speaking rate were obtained for the dysarthric speakers. Results revealed that dysarthric speakers exhibited smaller vowel space areas and less systematic changes in vowel space as a function of speaking rate, when compared to the neurologically intact speakers. In an examination of the relationship between vowel space area and speech intelligibility, vowel space was found to account for 45% of the variance in speech intelligibility. This result suggests that vowel space area is an important component of global estimates of speech intelligibility.

Dynamic aspects of lower lip movement in parkinsonian and neurologically normal geriatric speakers' production of stress.

Lower lip+jaw movement was evaluated for parkinsonian dysarthric and age-matched, neurologically normal speakers during the production of alternating stress contrasts. Discrete measures of movement, including displacement amplitude, peak velocity, the relation of amplitude to peak velocity, and movement durations were compared across groups for stressed and unstressed syllables. Additionally, quantitative (parameter c and the ratio of acceleration to deceleration) and qualitative indices of dynamic characteristics of velocity profiles for lower lip+jaw opening and closing gestures were compared across the subject groups. Within the dysarthric group, the relation between each discrete and dynamic kinematic parameter and the perceived severity of the dysarthria was investigated. The discrete measures confirmed previous findings of reduced displacement and peak velocity for the parkinsonian speakers during opening and closing gestures for both the stressed and unstressed syllables. However, the relation between amplitude and velocity did not differ for the two subject groups for any gesture. Movement durations were equivalent for the two groups during the production of opening gestures, but were significantly shorter for the parkinsonian speakers during closing gestures. Quantitative indices of the velocity profiles also failed to differentiate between the subject groups or between dysarthric speakers as a function of severity. By contrast, the qualitative descriptions of the velocity profiles showed between-speaker differences that were more pronounced for subjects with more severe dysarthria. These qualitative differences were evident in opening gestures toward an unstressed vowel, only.

Perspectives on the Edinburgh study of speech breathing.

This article offers critical perspectives on the Edinburgh study of speech breathing reported in this journal (Draper, Ladefoged, & Whitteridge, 1959) and elsewhere (Draper, Ladefoged, & Whitteridge, 1960; Ladefoged, Draper, & Whitteridge, 1958). These perspectives concern: (a) errors in establishing a backdrop of mechanical information; (b) discrepancies between data and statements about them; (c) counterpredictive features between data and other knowledge about breathing; and (d) inadequacies in acquiring, portraying, and interpreting electromyographic information relative to the muscular contributions of different parts of the breathing apparatus.

Evaluation of a reiterant force-impulse task in the tongue.

In the current study characteristics of a lingual force-impulse task were examined. In the task, neurologically normal adults were required to produce sequences of lingual force impulses that were modeled on sequences of syllables produced as reiterant speech. The goal of data analysis was to (a) compare the timing of the reiterant force sequences to the timing of reiterant speech sequences, (b) compare the force magnitudes to expected force variations associated with linguistic stress in the reiterant speech sequences, and (c) compare the reiterant force magnitudes to maximum lingual forces. Results indicated that reiterant force timing is typically slower than reiterant speech timing, that reiterant force magnitudes do not vary systematically as a function of stress variations in the reiterant speech utterances, and that reiterant force magnitudes are typically only a fraction of maximum lingual forces. Results are discussed in terms of the relationship between orofacial, nonspeech motor performance and speech production performance.

Spectral analysis of target-appropriate /t/ and /k/ produced by phonologically disordered and normally articulating children.

Previous research (Forrest, Weismer, Hodge, Dinnsen and Elbert, 1990) has shown that some phonologically disordered children differentially mark seemingly homophonous phonemes; however, the resulting contrast may be spectrally distinct from that produced by normally articulating children of the same age. In the present investigation possible sources for these differences between normally articulating and phonologically disordered children's productions of target-appropriate phonemes were pursued. Spectral characteristics of seemingly correct productions of /t/ and /k/ in word-initial position were analysed for four normally articulating and seven phonologically disordered children to assess the effect of recency of acquisition, depth of knowledge of the contrast and/or the effect of a phonological disorder on accuracy and variability of production. Results revealed that children who had acquired the velar-alveolar contrast more recently, and who had incomplete knowledge of that contrast, produced target-appropriate /t/ and /k/ differently from their normally articulating peers and other phonologically disordered children with greater knowledge of the contrast. Further, the phonologically disordered children with incomplete knowledge of the velar-alveolar contrast were less variable than the other phonologically disordered or normally articulating children in the spectral characteristics across repeated productions. Analysis of the spectral characteristics of word-initial /t/ and /k/ at a later point in time indicated similarities between all speaker groups in the spectral parameters that distinguished the velar from the alveolar stop. However, the stability of these parameters across repeated productions decreased for the phonologically disordered children with greater knowledge of the contrast. These effects are related to motor skill development and found to be consistent with previously demonstrated patterns of skill acquisition.

Characteristics of speaking rate in the dysarthria associated with amyotrophic lateral sclerosis.

The ability to alter speaking rate was studied in a group of 9 subjects with amyotrophic lateral sclerosis (ALS) and 9 age- and gender-matched, neurologically intact controls. Subjects were instructed to speak at three different rates (i.e., habitual, twice as fast as habitual, and one-half as fast as habitual). Speaking rate, articulation rate, and pause duration and frequency were calculated. The proportional increase in speaking rate was similar between the groups; however, the dysarthric speakers slowed rate to a smaller extent. Articulation rate and pause duration and frequency covaried with speaking rate in a similar manner for both groups. There was evidence that dysarthric speakers showed a greater dependence on pause duration and frequency, as compared to articulation rate, especially when increasing rate. In addition, although it was found that the slope of the function relating phrase duration to phrase length in syllables was statistically significant for both normal and dysarthric speakers, the slope of the function was significantly more shallow for the dysarthric speakers. Perceptual judgments of speaking rate indicated that dysarthric speakers spoke faster for a given physical speaking rate. Finally, results suggested that the function relating physical to perceived speaking rate grew more rapidly for dysarthric as compared to normal speakers. Discussion focuses on the importance of these findings to rate manipulation therapies and models of speaking rate in dysarthric speech.

Speaking rate and speech movement velocity profiles.

The effects of speaking rate on the velocity profiles of movements of the lower lip and tongue tip during the production of stop consonants were examined using an x-ray microbeam system. Five young adults used a magnitude production task to produce five speaking rates that ranged from very fast to very slow. Results indicated that changes in speaking rate were associated with changes in the topology of the speech movement velocity-time function. Specifically, the velocity profile changed from a symmetrical, single-peaked function at the fast speaking rates to an asymmetrical and multi-peaked function at the slow speaking rates. This variation in velocity profile shape is interpreted as support for the view that alterations in speaking rate are associated with changes in motor control strategies. In particular, the control strategy for speech gestures produced at fast speaking rates appears to involve unitary movements that may be predominantly preprogrammed, whereas gestures produced at slow speaking rates consist of multiple submovements that may be influenced by feedback mechanisms.

Qualitative acoustic analysis in the study of motor speech disorders.

Traditional measurements performed on the acoustic signals of normal speech are frequently used to quantify the acoustic characteristics of disordered speech as well. This letter demonstrates how important aspects of speech production deficits in motor speech disorders may be overlooked if stringent quantification procedures are employed, especially in the stage of exploratory data analysis. It is suggested that qualitative procedures, wherein phenomena are inferred from visual examination of certain acoustic displays, are useful to supplement traditional measurements, and moreover, that they be used to point to the types of measurements that should be made in the finer-grained stages of quantitative analysis.