The purpose of this study was to measure velopharyngeal closure force in varying phonetic contexts for normal men and women subjects. Levator veli palatini muscle activity was measured as well. Place and manner of articulation, voicing and the effects of consonant sequencing were studied in different vowel contexts. When the data were grouped by sex of subject, no differences were found in absolute values of velopharyngeal closure force for the men versus women subjects. As expected, nonnasal consonants were produced with greater velopharyngeal closure force than nasal consonants. High vowels were produced with greater closure force than low vowels. Closure force was greater for voiceless than for voiced consonants but only for the men and only within /i/ and /u/ contexts. The lingua-dorsal consonant was associated with greater closure force than the lingua-apical consonant but only for the men and only in the high-back vowel environment. Significant differences in closure force were not found between fricatives or stops. A tendency for greater closure force for the fricative consonant was observed when the fricative followed rather than preceded the nasal consonant. Vowel identity had an effect on closure force during consonant production in the men in that closure force was greater for /s/ and /n/ in high versus low vowel contexts. Men exhibited a larger number of significant differences in closure force than did the women. The results suggest that velopharyngeal closure force is not controlled by a single muscle (the levator veli palatini) but that other muscles and mechanical factors are likely contributors.
This paper considers the possible role of nonspeech tasks in the assessment of individuals with motor speech disorders. The difficulties in the definition and isolation of both speech and nonspeech tasks are discussed. A primary point is that an inability to control the movements of the speech structures may be separate from an inability or ability to use the processes that code meaning in the construction of linguistic messages. It may be possible to design nonspeech tasks that provide insight into an individual's ability or inability to control speech movements, but are separate from his or her ability to use language.
A comparison of the ranges of levator veli palatini EMG activity for speech versus a nonspeech task for subjects with cleft palate was the focus of this study. EMG values are also compared with subjects without cleft palate obtained in a previous study. Hooked-wire electrodes were inserted into the levator muscle of five adult subjects with cleft palate exhibiting mild hypernasality. Intraoral air pressure was measured concurrently. A blowing task was used to determine the subject's operating range for the levator muscle. Both the nonspeech and speech tasks were designed to sample the widest possible ranges of levator EMG activity. It was found that the subjects with cleft palate used a relatively high activation level for the levator muscle during speech, in relation to their total activation range, compared with the subjects without cleft palate. Implications are discussed in relation to possible anatomic and physiologic differences for cleft palate subjects compared to normal.
Assessment of the role of gravitational forces in the motor control of the velopharyngeal mechanism was the focus of this study. Specifically, the effect of gravity on activation levels of the levator veli palatini and palatoglossus muscles was assessed. Nineteen volunteers repeated a CV syllable in upright and supine body positions. Overall, lower peak activation levels of levator veli palatini were observed in the supine body position. The results suggest that less muscle activity was seen in the levator veli palatini in the supine body posture, where gravitational effects worked in the same direction (i.e. toward closure). No statistically significant group effects were seen in muscle activation levels of palatoglossus across the two body postures, although clear gravity effects were observed in some subjects. The implications of these findings from a speech motor control perspective are discussed in relation to normal and disordered velopharyngeal function.
The purpose of this investigation was to study the operating range of the levator veli palatini muscle for a nonspeech task (blowing) and to determine where in that range levator activity for speech lies. Ten adult subjects without speech or velopharyngeal abnormalities participated. Levator EMG activity for speech occurred in the lower region of the total range for blowing. In two subsequent experiments involving a subset of 4 subjects, it was found that overall effort may have had a small effect on levator activity apart from its role in velopharyngeal closure for aerodynamic purposes. The results of the main experiment are discussed in relation to the concept of threshold of fatigue as it may influence velopharyngeal control mechanisms.
The present study reports data from apraxic and non-brain-damaged speakers on phase relationship and cross-correlation of tracking. It was expected that apraxic speakers would have lower correlations than would normal speakers in all conditions. It was also hypothesized that apraxic speakers would phase-lag predictable targets, whereas non-brain-damaged speakers would evidence phase synchrony or lead. Finally, it was anticipated that all subjects would show phase lag during nonpredictable tracking. If apraxic subjects performed poorly on both predictable and non-predictable tracking, then one could argue that motor control, regardless of tracking mode (internal or external), was impaired. If apraxic speakers performed better on predictable tracking than they did on nonpredictable tracking, it could be hypothesized that they were able to develop an internal model or plan but had difficulty executing the movements in a coordinated manner. If, however, apraxic speakers performed better on nonpredictive tracking than predictive tracking, then one could hypothesize that these subjects did not generate an internal plan to predict movement outcomes but were able to follow an external target that required no such predictive strategy. Thus, the motor control problem would be at the planning or predictive stage of movement execution, and the movements for predictable targets would be jerky rather than smooth.
Patients with mild velopharyngeal incompetence (VPI) may have speech disorders, which are not sufficiently severe to warrant extensive surgical intervention, yet may not be amenable to correction by speech therapy alone. Augmentation of the posterior pharyngeal wall to aid in closure of the velopharyngeal sphincter may be beneficial in establishing better speech patterns, especially when combined with speech therapy. A variety of materials and techniques have been used in the past for this purpose. In this setting, autogenous fat may be transplanted without the risks incurred by augmentation with synthetic materials and involves very little donor site morbidity. The literature is somewhat contradictory, however, regarding the stability of the augmentation achieved using autogenous fat and there are no histologic studies describing the fate of the fat injected into tissues of the oral cavity. Prior to introduction of this technique into clinical practice, this study was designed to investigate the fate of autogenous fat injected submucosally in the oropharyngeal region. Autogenous fat was injected into the anterior soft palate using the rabbit as a model. Histologic and gross inspections were performed at 2 days, 1, 2 and 4 weeks after injections. At the end of 4 weeks, at least 50% of the injection sites had visible evidence of augmentation, and 90% had histologic evidence of submucosal fat. In some instances most of the fat was resorbed; however, there were no instances of clinical infection or necrosis of the injection site. We conclude that submucosal injection of autogenous fat is a feasible alternative to using synthetic or other biologic materials for augmentation in the oral cavity.
The purposes of this study were to (a) design and test a new velopharyngeal closure force sensing bulb, and (b) use the closure force bulb to gather additional information on the variations in closure force associated with different vowels. The closure force sensing bulb possessed a flat frequency response to 30 Hz. Its output was highly linear relative to applied gram force. Reliable placement of the bulb in human subjects was achieved following prescribed placement criteria. The bulb was sensitive to small variations in velopharyngeal closure force. In agreement with some previous reports, high vowels were associated with greater velopharyngeal closure forces than low vowels. The results of this investigation support the notion that articulatory goals are specified for vowels. This vowel specificity was observed during production in both isolation and in context.
The relative contributions of the levator veli palatini, palatoglossus, and palatopharyngeus muscles were assessed relative to a range of positions of the velopharynx during production of the vowels [a] and [i] by four normal adult speakers. The results indicate that velopharyngeal positioning is determined by the relative contributions of the levator veli palatini, palatoglossus, and palatopharyngeus muscles. There was an increase in coefficients of determination (i.e., amount of closure level variability explained) when activity levels of all three muscles are included in the statistical model compared to activity in any one muscle analyzed independently. Both consistent and inconsistent relations among activity levels in three velopharyngeal muscles studied were observed across speaker and vowel produced.
This study was conducted to (a) study the ability of young adult subjects to track target signals with the lower lip, jaw or larynx, (b) examine subjects' abilities to track different sinusoidal frequencies and unpredictable target signals, and (c) test notions of response mode and predictive mode tracking reported for nonspeech structures by previous authors (e.g., Noble, Fitts & Warren, 1955; Flowers 1978). Twenty-five normal speakers tracked sinusoidal and unpredictable target signals using lower lip and jaw movement and fundamental frequency modulation. Tracking accuracy varied as a function of target frequency and articulator used to track. The results quantify the visuomotor tracking abilities of normal speakers using speech musculature and show the potential of visuomotor tracking tasks in the assessment of speech articulatory control.
Continuous positive airway pressure (CPAP) therapy can be used to reduce hypernasality by elevating the air pressure in the nasal cavities during speech. The purpose of this study was to determine whether increased intranasal air pressure loads the major muscle of velopharyngeal closure, the levator veli palatini. Nine subjects, four with cleft palate and five without cleft palate, were studied. Electromyographic activity was measured from the levator veli palatini muscle with several levels of air pressure delivered to the nasal cavities using a commercially available CPAP instrument. It was found that levator veli palatini activity was significantly greater for the positive air pressure conditions than for the atmospheric pressure conditions for both subject groups. This indicates that the levator veli palatini muscle acts against the resistive load produced by the increased intranasal air pressure. The results support the use of CPAP therapy as a method of resistance exercise for strengthening velopharyngeal closure muscles.
Vocal tract pressures during speech tend to be maintained in the face of airway leaks that might be encountered by individuals with repaired palatal clefts. This study tested the hypothesis that such constant pressures can be explained as a consequence of constant pressure source characteristics of the respiratory system during speech production. This conceptualization differs from pressure regulation theories [e.g., Warren, Cleft Palate J. 23, 251-260 (1986)] which posit that active reflexive compensatory responses occur to regulate air pressure during speech. Four experiments were conducted to (a) confirm the distinction between constant flow versus constant pressure sources using a plastic vocal tract model, (b) compare air pressure and flow patterns associated with airway leaks in normal speakers to model data, (c) study the effects of gas density in the vocal tract model on air pressure and air flow patterns predicted by a nonreflexive constant pressure source hypothesis, and (d) compare air pressure and air flow patterns associated with airway leaks obtained from normal speakers using different gas densities to model data. Overall, observed flow and pressure patterns suggest the possible influence of constant pressure source characteristics of the respiratory system during speech on maintenance of intraoral air pressure.
Previous experimental evidence has been interpreted as support for regulation of both acoustics and aerodynamics during speech production. One recent perspective is that although speech acoustics may be manipulated, regulation of aerodynamics is a central component of the processes that produce speech. From this perspective, it has been suggested that aerodynamic regulation is given priority over perceptual accuracy. The experiment attempted to test this hypothesis by forcing speakers into a choice between aerodynamic and acoustic regulation. The intensity level of frication (embedded in a carrier phrase) was selectively amplified or attenuated and fed back to the speaker on line. Intraoral air pressure was recorded in order to assess whether or not perturbed auditory feedback would result in aerodynamic compensation. Although compensatory changes in peak intraoral air pressure, pressure duration and pressure curve areas were seen in response to 30-dB alterations of frication, no systematic effects ere seen for smaller auditory manipulations. Further, the compensations were less than what one might expect from a system controlling auditory output. Explanations of these findings and their implications for the control of speech production are offered.
This investigation was designed to measure the ability of normal adult speakers to exert voluntary control over velopharyngeal positioning. Speakers were asked to phonate the vowels [a] and [i] at 50 percent and 75 percent of complete velopharyngeal closure, using visual feedback of velopharyngeal opening and closing gestures from a phototransducer. The musculature of the velopharyngeal mechanism was hypothesized to act as a coordinated system that may demonstrate both motor flexibility and plasticity (Folkins, 1985) when forced to function in a novel way. Evidence of both motor system responses to a novel speaking condition was observed. Speakers were able either to phonate at intermediate closure levels without having to learn new motor rules, or to learn new rules for velopharyngeal muscle activation that resulted in the ability over time to position the velopharyngeal mechanism appropriately. As such, support is derived from the notion (Folkins, 1985) that speakers develop motor rules or coordinative structures involving the velopharyngeal mechanism that govern velopharyngeal movement. The characteristics of this coordinative structure framework have not yet been described, however, and are the subject of ongoing research efforts.
The transmission characteristics of nasal tract energy to a nasal accelerometer were evaluated in relation to nasal tract airway resistance. Ten adult speakers repeated three utterances while recordings of nasal bone vibration, as detected by miniature accelerometers, were obtained simultaneously from both sides of the nose and referenced to a common throat signal. Average nasal-to-oral accelerometry ratios recorded from the more resistant side of the nose were significantly larger in magnitude than those recorded simultaneously from the less resistant side of the nose. While accelerometer ratio waveforms from each side of the nose essentially overlapped for some subjects, others displayed unilateral variations in accelerometer output as a function of time. The anatomic and physiologic condition of the nasal passage appears to be an important variable in the detection of nasal tract acoustic energy using the accelerometric technique.