John W. Folkins

An integrative model of speech motor control: A response to Ziegler

Background : Ziegler (2003) reviews neural and behavioural evidence to support a task-dependent model of motor control, whereby motor speech disorders represent impairment of a sensory-minor system specialised for speech. Based on this approach, Ziegler argues against the examination of volitional or novel nonspeech motor activities to gain insight into motor control for speech. Aims : The primary objective of this paper is to discuss Zieglers (2003) conceptualisation of the task-dependent model and present an alternative integrative model. In the latter, speech and volitional nonspeech motor control are integrated into the functioning of a more general motor system where neural and behavioural systems demonstrate areas of overlap. Studies of the nervous system, the evolutionary foundations of speech in great apes, behaviour, and motor learning are presented to support an integrative model of motor control. Main Contribution : Neurological and evolutionary evidence strongly suggest that neural networks are flexible, multifaceted, multifunctional and overlapping in function. It is highly likely that a higher-level behaviour like speech involves networks that are similarly multifunctional and overlapping with other motor functions. Zieglers concept of task-dependent motor control may relate as much to parameters such as complexity, familiarity, and automaticity of task performance as to the nonpeech-speech distinction. Studies are reviewed that support the inclusion of nonspeech motor tasks in assessment of the disordered speech motor control system. Specific nonspeech tasks clearly facilitate differential diagnosis and provide insight into the functioning breakdown of the motor system for related but more complex speech behaviours. Finally, motor learing studies are discussed with particular reference to how these might inform models of motor control. Conclusions : This response cautions against the seemingly premature acceptance of a model assuming separate sensory motor systems for volitional nonspeech motor activities and speech. Continued research, without the limitations imposed by such an assumption, is required to enhance understanding of component parts of complex behaviours and how those components interact in normal and damaged systems at different levels of a performance. These data have the potential to form the basis for new, more effective approaches to treatment of motor speech disorders.

Coordination of Velopharyngeal Muscle Activity during Positioning of the Soft Palate

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 the three velopharyngeal muscles studied were observed across speaker and vowel produced.

Lip and jaw interaction during speech: Responses to perturbation of lower‐lip movement prior to bilabial closure

Electrical stimulation was used to produce unexpected, involuntary depression of the lower lip in three normal young adults. Stimulation was timed to begin 500 to 40 ms prior to voice offset in [aep] and (Ip]. Upper lip, lower lip, and jaw movements were measured with a strain gauge system. Movements in 104 syllables with lower-lip stimulation were compared to the preceding normal syllable. Both the jaw and upper lip compensated for the involuntary perturbations in lower-lip movement. Compensatory movements did not occur as additional, discrete gestures following stimulation onset, but appeared as an increase in the size of closing movements. Bilabial closure was produced at the typical time (within - 10 to + 20 ms of voice offset) in 68% of the perturbed syllables, but it was delayed (a mean of 61 ms) in the remaining 32%. Neither the incidence nor the magnitude of this delay appeared to be related to the jaw position at stimulation onset or to the time between stimulation onset and voice offset.

What can nonspeech tasks tell us about speech motor disabilities

Abstract This paper considers the possible role of nonspeech tasks in theassessment 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 individuals ability or inability to control speech movements, but are separate from his or her ability to use language.

Air pressure regulation during speech productiona)

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., D. 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 press...

Jaw‐muscle activity during speech with the mandible fixed

Electromyographic recordings were made from the anterior temporalis, masseter, medial pterygoid, and lateral pterygoid muscles in four normal adult subjects. Discrete bursts of activity occurred in these muscles even during speech with the jaw prevented from moving by placement of a bite block between upper and lower molars. The bursts of muscle activity with the bite block were similar in frequency of occurrence, time of peak activity, and magnitude to the activity observed with the jaw free to move. A motor control system that employs a central simulation process to coordinate the lips and tongue with the jaw is not necessarily consistent with this finding. An efficient central simulation process might be expected to eliminate the discrete jaw-muscle activity with the jaw fixed as well as producing correct responses in the lips and tongue. These data are more consistent with a motor control system employing lower-level neural mechanisms to coordinate articulatory movements.

Upper lip, lower lip, and jaw interactions during speech: comments on evidence from repetition-to-repetition variability

Six studies purporting to demonstrate complementary covariation in lip and jaw activity during speech are reviewed. The statistical procedures used to assess interactions among the upper lip, lower lip, and jaw movements are discussed for four different experiments analyzing repetition-to-repetition movement variation. The findings from two studies analyzing repetition-to-repetition variation for interactions in electromyographic activity recorded from either the jaw musculature or the labial musculature also are evaluated. It is concluded that these studies do not provide convincing evidence of complementary covariation among the articulators or the muscles.

The role of the perioral reflex in lip motor control for speech

Abstract The analysis of spinal and brainstem reflexes has been shown to be a useful method of quantifying the various inputs to motoneuron pools involved in voluntary motor control. This work is selectively reviewed as a background to a discussion of the role of the perioral reflex in lip motor control for speech. Data on the sensorimotor innervation of the lips and the static and dynamic properties of the perioral reflex are presented in support of the notions that (1) perioral reflex analysis provides a viable technique for analyzing brainstem excitability changes underlying lip muscle contraction for speech, and (2) the perioral reflex loop is an important functional element in lip motor control for speech.

The effects of auditory feedback on the regulation of intraoral air pressure during speech

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 area were seen in response to 30-dB alterations of frication, no systematic effects were 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.

Jaw and lip movements of deaf talkers producing utterances with known stress patterns

This investigation determined whether prelingually deaf talkers could correctly produce stressed and unstressed syllables across known changes in stress patterning and phonetic composition. Three deaf and three hearing adults spoke sets of homogeneous syllable strings with stress patterns that they could tap successfully with a finger. Strain gauge transduction of lower lip and jaw movement indicated that both deaf and hearing subjects produced different displacements and durations for the stressed and unstressed syllables, regardless of the stress pattern. Jaw movement did not become more variable with changes in phonetic composition of the syllables. The results show no evidence that motoric abilities (as assessed in lip and jaw movements) limit deaf talkers in producing desired stress patterns.