James H. Abbs

Control of multimovement coordination: sensorimotor mechanisms in speech motor programming.

The present paper provides some hypotheses concerning the role of sensorimotor mechanisms in the coordination and programming of multimovement behaviors. The primary database is from experiments on the control of speech, a motor behavior that inherently requires multimovement coordination. From these data, it appears that coordination may be implemented by calibrated, sensorimotor actions which couple multiple movements for the accomplishment of common functional goals. The data from speech and select observations in other motor systems also reveal that these sensorimotor linkages are task-dependent and may underlie the intermovement motor equivalence that characterizes many natural motor behaviors. In this context, it is hypothesized also that motor learning may involve the calibration of these intermovement sensorimotor actions. These observations in turn provide some alternative perspectives on the concept of a motor program, primarily suggesting that individual movements and muscle contractions are not wholly prespecified, but shaped by sensorimotor adjustments.

Labial-Mandibular Coordination in the Production of Speech: Implications for the Operation of Motor Equivalence

The purpose of this study was to explore select properties of speech movement coordination. Values of displacement for the upper lip, lower lip and jaw were obtained during repetitive productions of three vowels (ae, i, xi, in CVCVC contexts) by six subjects at two speaking rates. These data were analyzed to determine the relative contribution of each of these articulators to the superior-inferior distance between the upper and lower lips. The results of these analyses provided substantive evidence for the operation of motor equivalence in the speech movement coordination of the labial-mandibular system. The theoretical implications of these findings for the neural control mechanisms underlying speech movements are discussed.

Functional muscle partitioning during voluntary movement: Facial muscle activity for speech

Electromyographic activity was recorded from multiple intramuscular sites in the orbicularis oris muscle for a set of speech and other motor tasks. Because of its geometric heterogeneity and multiple functions, it was hypothesized that this muscle might be partitioned in a task-dependent manner. Comparison of the timing and amplitude of the EMG activity among the multiple recording sites supported this hypothesis. Because some facial motoneurons in primates, including humans, are monosynaptically activated from area 4 of the motor cortex, it is suggested that this task-dependent muscle partitioning may reflect an aspect of cortical organization.

Hypoglossal, trigeminal, and facial motoneuron involvement in amyotrophic lateral sclerosis

Facial, trigeminal, and hypoglossal motoneuron involvement was quantified in 25 amyotrophic lateral sclerosis patients and in normal controls. Measures included (1) maximum voluntary contraction of the lower lip, mandible, and tongue using custom-designed force transducers, (2) clinical functions of each muscle group, and in some patients (3) orofacial mobility using videofluoroscopy. All measures indicated that the tongue muscles were most severely affected, even in patients who initially had symptoms in the extremities.

Mechanoreceptive afferent activity in the infraorbital nerve in man during speech and chewing movements

SummaryThe method of microneurography was used to record activity in trigeminal cutaneous and mucosal mechanoreceptive afferents during natural orofacial behaviors such as speech gestures, chewing, licking and swallowing. Multi-unit activity and impulses in single nerve fibers were recorded from the infraorbital nerve. It appeared that these mechanoreceptors respond to contact between the lips, air pressures generated for speech sounds, and to the deformation/strain changes of the facial skin and mucosa associated with various phases of voluntary lip and jaw movements. The relatively vigorous discharge of cutaneous and mucosal afferents during natural movements of the face are consistent with the claim that mechanoreceptors found within the facial skin provide proprioceptive information on facial movements.

Variant and invariant characteristics of speech movements.

SummaryUpper lip, lower lip, and jaw kinematics during select speech behaviors were studied in an attempt to identify potential invariant characteristics associated with this highly skilled motor behavior. Data indicated that speech motor actions are executed and planned presumably in terms of relatively invariant combined multimovement gestures. In contrast, the individual upper lip, lower lip, and jaw movements and their moment-to-moment coordination were executed in a variable manner, demonstrating substantial motor equivalence. Based on the trial-to-trial variability in the movement amplitudes, absolute positions, and velocities of the upper lip, lower lip, and jaw, it appears that speech motor planning is not formulated in terms of spatial coordinates. Seemingly, object-level planning for speech may be encoded in relation to the acoustic consequences of the movements and ultimately with regard to listeners auditory perceptions. In addition, certain temporal parameters among the three movements (relative times of movement onsets and velocity peaks) were related stereotypically, reflecting invariances characteristic of more automatic motor behaviors such as chewing and locomotion. These data thus appear to provide some additional insights into the hierarchy of multimovement control. At the top of the motor control hierarchy, the overall plan appears to be generated with explicit specification of certain temporal parameters. Subsequently, based upon the plan and within that stereotypic temporal framework, covariable adjustments among the individual movements are implemented. Given the results of previous perturbation studies, it is hypothesized that these covariable velocity and amplitude adjustments reflect the action of sensorimptor mechanisms.

Autogenic and nonautogenic sensorimotor actions in the control of multiarticulate hand movements

SummaryHuman subjects were trained to generate rapid movements of the thumb and index finger and produce a controlled pinch contact force. When unanticipated loads were applied to oppose thumb flexion movements, the desired pinch contact force was achieved by compensatory adjustments of both the thumb and the index finger flexor muscles. The nonautogenic finger muscle responses were (1) at latencies of 60 to 90 ms, (2) manifest the first time a load was introduced, and (3) absent for thumb loads introduced during a task not requiring coordination of thumb-finger actions. These intermovement sensorimotor mechanisms may reflect a general task-dependent process contributing to coordination of multiarticulate movements.

The relationship between parkinsonian rigidity and hypokinesia in the orofacial system A quantitative analysis

Muscle rigidity was quantified in the labial muscles of parkinsonian and normal subjects by applying known forces and observing the resultant displacements to determine labial stiffness coefficients. In parallel, labial speech movements were observed from these same subjects to evaluate hypokinesia. Labial rigidity was consistently correlated with decrements in the range of lip movement. EMG from orbicularis oris and mentalis muscles indicated a causal relationship between rigidity and hypokinesia.

Central patterning of speech movements.

SummaryPrevious speech kinematic studies have demonstrated systematic timing relations among the upper lip, lower lip, and jaw suggesting the operation of a central pattern generator (CPG). The present study evaluated the consistency of these timing relations following unanticipated perturbation of the lower lip. Using this approach, it was also possible to evaluate the influence of sensory information on the timing of motor output and subsequent coordination of the multiple speech movements. Perturbations were applied to the lower lip during the closing movement associated with the first “p” in “sapapple”. Muscle activity and movements of the upper lip, lower lip, and jaw were obtained. Changes in movement displacement, velocity and duration, the timing and sequencing of peak velocities, EMG area, and EMG rise time were analyzed for the control and load conditions. Similar to previous perturbation results, significant magnitude compensations from the muscles and movements of the upper lip, lower lip, and jaw were observed. In contrast, movement durations and the sequencing of peak velocities were relatively unaffected by the lower lip load. The timing of peak EMG amplitude and consequently the timing of peak closing velocity for all structures (UL, LL, and J) occurred earlier relative to the preceding opening movement. These results are consistent with the interaction of phasic sensory input with centrally-driven commands resulting in a phase-advanced motor output. Further, as the timing of one structure is modified so were all the functionally-linked components thereby maintaining the necessary coordination. As in other rhythmic motor behaviors such as locomotion and chewing, there appears to be a centrally patterned framework for speech movement coordination.

Orofacial fine motor control impairments in congenital spasticity Evidence against hypertonusrelated performance deficits

Motor impairments in the line force control of lips, tongue, and jaw were measured in subjects with congenital spasticity. Because these orofacial motor systems are not uniformly endowed with muscle spindles and monosynaptic reflexes, quantification of these motor impairments addresses the question of whether stretch reflex hypertonus is a positive or negative sign. The results indicated that hyperactive muscle spindle-based monosynaptic reflexes are not a causal factor in these voluntary orofacial motor impairments. These data also indicated that motor impairments were disproportionately greater at finer levels of isometric force control. These fine control measures appear useful as a quantitative index of general voluntary motor deficit.