Ben C. Watson

Fundamental frequency during phonetically governed devoicing in normal young and aged speakers

Age-related changes in the laryngeal system can be perceived as altered vocal pitch and increased pitch variability. However, reports vary as to the nature and extent of an age effect on fundamental frequency (F0) for analyses taken over long segments of connected speech. Analysis of F0 across a smaller time frame may be more informative. Young speakers show an increase in F0 associated with phonetically governed devoicing gestures that is likely mediated by increased vocal fold stiffness. Anatomic and neurophysiologic changes in the aged larynx may limit the role of increased vocal fold stiffness in the devoicing gesture. This study tests the hypothesis that aged speakers show a smaller increase in F0 in association with the devoicing gesture for production of an intervocalic voiceless obstruent than do young speakers. Normal young and aged speakers produced a short sentence containing an intervocalic voiceless obstruent. Measures of F0 were obtained for ten cycles before voice offset and ten cycles after voice onset. Young speakers showed a small increase in F0 during devoicing whereas aged speakers showed a decrease in F0 during devoicing. Aged speakers seem to rely more on vocal fold abduction rather than a combination of abduction and tensing to achieve devoicing.

Linguistic performance deficits in stutterers : relation to laryngeal reaction time profiles

Abstract Converging evidence suggests that stuttering is associated with deficits in the planning and execution of speech. Evidence also suggests that the onset, development, and loci of stuttering are related to demands language places on speech motor planning and execution. We combined linguistic and vocal motor assessments to address two questions: 1) Can we identify a subgroup of adult stutterers who demonstrate linguistic deficits? and 2) Do linguistically normal and impaired stutterers show different patterns of laryngeal reaction time (LRT) as a function of response complexity? Linguistic performance was evaluated using tasks that assess relatively high-level production and comprehension processes. Responses used to record LRT differed in linguistic and motoric complexity. Only linguistically impaired stutterers showed significant increases in LRT for complex responses. Findings suggest that linguistic and motor processes affect the efficiency and fluency of speech motor control and that both processes be made explicit in models of stuttering.

Multichannel electromyographic observations in spasmodic dysphonia patients and normal control subjects.

Spasmodic dysphonia is primarily a disorder of vocalization. Increasing evidence, however, suggests that individuals with this disorder comprise a heterogeneous population characterized by abnormal motor control throughout the vocal tract. Multichannel simultaneous electromyography was performed on 11 spasmodic dysphonia patients and 10 normal awake subjects to investigate both the distribution of neuromotor abnormality within the vocal tract (eg, intrinsic and extrinsic laryngeal muscles, tongue, and palate) and the contribution of activation of higher central nervous system centers to observed abnormality. Experimental tasks ranged from vegetative (quiet breathing) to simple linguistic (short sentences). Digitized electromyographic signals were analyzed to compute the amplitude envelope and extract a set of parameters that represent amplitude characteristics. Electrode insertions were cross-validated by quantitative analysis of patterns of activation across selected reference tasks and by traditional qualitative methods. Between-group differences were found for measures of normalized median and peak token amplitudes. These differences are both task- and measure-dependent. Results highlight the complex and interactive effects of muscle, task, and quantitative measures on between-group differences.

Foreperiod duration, range, and ordering effects on acoustic LRT in normal speakers

One quantitative measure of vocal motor control is phonation onset latency relative to presentation of an external stimulus in a reaction time task. However, variables within the design of reaction time experiments can affect laryngeal reaction time (LRT) values. The present study examines effects of foreperiod characteristics on LRT for normal speakers. Foreperiod is the interval between presentation of warning and response cues. LRT was affected by absolute foreperiod duration, by the average foreperiod duration of a block of trials, and by the ordering and range of foreperiods within a block of trials. Results are discussed with respect to foreperiod effects on the subjective expectancy and objective probability of occurrence of the response cue and on the timing of neurophysiologic processes. Control of subjective effects is critical to assessment of neurophysiologic constraints on LRT.

Respiratory/Laryngeal Coupling and Complexity Effects on Acoustic Laryngeal Reaction Time in Normal Speakers

Summary The simple reaction time paradigm was used to investigate effects of peripheral (respiratory/laryngeal coupling) and central (task complexity) requirements on average acoustic laryngeal reaction time (LRT) values in normal speakers. Respiratory/laryngeal coupling at response onset varied from glottal stop to aspirate. Complexity varied from isolated vowel to short sentence. The range from shortest to longest average LRT value across all tasks was 69 ms. Significant differences among tasks indicate that acoustic LRT values are sensitive to relatively small magnitude effects associated with respiratory/laryngeal coupling and task complexity. Results led to formulation of two hypotheses, which, while consistent with present findings, require further investigation: First, LRT increases directly with increasing glottal resistance. Second, LRT increases directly with increases in the number of stressed syllables in the response.

An instrumented method for assessment and remediation of stuttering: A single-subject case study☆

Abstract A single-subject experimental design was used to investigate the feasibility of applying non-invasive laboratory instrumentation for examining speech physiology to assessment and biofeedback-based remediation of stuttering. Physiologic assessment facilitated the development of behavioral goals directed at changing respiratory and phonatory behaviors for this subject. Visual biofeedback therapy produced reduction in respiratory discontinuities and increased phonatory continuity, concomitant with reduced perceivable molar dysfluency. Methods used in this case illustrate a variety of options and problems related to clinical use of instrumentation. Results suggest that signals which represent respiratory, phonatory, and articulatory physiologic events may be clinically practical for evaluating and altering perceivable dysfluency.

Measuring Stutterers’ Dynamical Vocal Tract Characteristics by X-ray Microbeam Pallet Tracking

Stuttering is generally considered to be a disorder of motor timing, yet neither the nature of the spatiotemporal interruptions of speech movements nor the physiological level(s) at which they occur is sufficiently understood. In particular, two critical questions that bear on the nature and treatment of stuttering, and by extension, the role of timing in various aspects of normal speech production remain unanswered. The first question concerns the anatomical locus of disordered motor timing. To what extent is the aberrant neuromuscular and kinematic activity that is associated with moments of stuttering specific to a single anatomical structure rather than spread throughout the speech production system? An aberrant state associated with a single structure, the larynx for example, might trigger abnormal activity in the respiratory and/or supralaryngeal systems. In this example, where laryngeal dysfunction precedes respiratory and supralaryngeal dysfunction, the activity of the latter systems might be viewed as compensatory rather than as an integral part of the stuttering breakdown. That is, the respiratory and supralaryngeal systems might be functioning to maintain appropriate temporal relationships with the abnormal laryngeal gestures.

Coordination of Prephonatory Events in Mild and Severe Stutterers

Many physiologically-based models of stuttering that associate laryngeal dysfunction with the disorder (Van Riper, 1971; Adams, 1978; Zimmermann, Smith & Hanley, 1981) share the hypothesis that stutterers have difficulty controlling the rapid initiation and termination of voicing. This hypothesis is supported by behavioral and physiological data drawn from samples of stutterers’ connected speech. Behavioral data show that stutterers demonstrate greater frequency of disfluency and less adaptation when reading aloud passages containing both voiced and voiceless segments than passages containing only voiced segments (Adams and Reis, 1971, 1974; Adams, Riemenschnieder, Metz & Conture, 1975). Physiologic data, obtained from fiberoptic viewing of the vocal folds (Conture, McCall & Brewer, 1977) and the recording of electromyographic (EMG) signals from intrinsic laryngeal muscles (Freeman and Ushijima, 1978; Shapiro, 1980), reveal evidence of abnormal laryngeal activity during stutterers’ disfluent utterances.

Systems Architecture for Quantification of Dynamic Myoelectric and Kinematic Activity of the Human Vocal Tract

This paper describes a systems architecture useful for scientific investigations that require the acquisition and analysis of multiple, time-synchronous signals in large volume. The architecture has recently been developed by this group to enhance our capability to research and quantify central nervous system function in the production of normal and pathologic speech. The architecture utilizes modern advances in desktop microcomputers and has been designed so that vocal motor control laboratories (or similar settings) with modest funding can more fully participate in comprehensive investigations of speech production. Research experiments organized with this architecture may involve many more subjects and measures than previously possible without significant increases in time and personnel resources. This paper will demonstrate the technique and practicality of this architecture as it is being used to successfully guide research to map hierarchic central nervous system regions of involvement in two speech disorders: Spasmodic dysphonia and stuttering. The architecture has broad usefulness to many areas of otolaryngology and health science.

Response complexity effects on vocal reaction time in normal aged speakers.

Reaction time (RT) studies reveal that vocal responses present an exception to the pervasive finding of slowed performance in aged adults. Previous vocal RT studies that compared young and aged speakers elicited a single‐word response. Inconsistent findings may be attributed to their use of a limited range of response complexity. Young speakers show a significant increase in vocal RT from vowel to sentence responses [Watson et al., J. Voice 5, 18–28 (1991)]. This study tested the hypothesis that aged speakers in good physiologic condition show significantly longer vocal RT values relative to young speakers as responses increase in complexity. Vocal RT was recorded for isolated vowel, word, and sentence responses. The simple RT paradigm included variable foreperiods and intertrial intervals. Young subjects ranged from 24–31 yr. Aged subjects ranged from 68–85 yr. Group, response, and group x response effects were significant. Post hoc comparisons revealed significant between‐group vocal RT differences for ...