Lip muscle activity related to speech rate and loudness.

Changes in suprasegmental speech parameters may require adjustments in oral motor control that are reflected in the activity of perioral musculature. In order to evaluate possible patterns of difference, perioral surface electromyographic (EMG) signals were obtained from 20 adults who read a paragraph aloud at habitual rate and at self-judged proportionately slower and faster rates, at habitual loudness and at proportionately softer and louder levels, and in a "precise" manner. EMG amplitude analysis showed significant task effects, with higher average amplitudes for fast, loud, and precise speech and lower average amplitudes for slow and soft speech. These results are compatible with a model of multidimensional reorganization of speech motor control for suprasegmental changes applied to connected speech.

Spatiotemporal stability of lip movements in older adult speakers.

Although the intelligibility of healthy older adults normally seems unimpaired, age-related changes occur in sensorimotor components of the speech system and in such global parameters as speech rate. In order to clarify the effect of these changes on the variability of speech movements, we examined oral peripheral abilities, speech rate, and speech kinematics in a group of 10 adults age 76-83, compared to a group of 10 young adults. Participants repeated a short phrase 15 times at habitual, fast, and slow rates. The resulting lip displacement signals were time- and amplitude-normalized, and successive standard deviations along the movement waveforms were summed to produce a spatiotemporal index (STI) representing individual variability in movement pattern. Participants tended to show greatest variability at slow rate, less variability at fast rate, and least variability at habitual rate. For the older adults, STI at habitual rate was significantly higher (more variable) and speech durations were longer than those of young adults. Perioral strength and tactile acuity were poorer in these older adults than in young adults. We conclude that as sensorimotor abilities change in old age, speakers are less consistent in the spatiotemporal organization of speech movements, reflecting decreased stability of speech motor control.

Tactile perception of spatial stimuli on the lip surface by young and older adults.

Although older adults are subject to both subtle changes and major disorders of the oral sensorimotor system, relatively little is known about oral sensory function in old age. Accurate assessment of oral tactile perception is needed to document disability, aid prognosis, and plan treatment for older adults with disorders affecting speech or feeding. However, normative information currently available for older adults is mainly based on two-point discrimination, a problematic measure of tactile spatial resolution. Grating orientation discrimination, a technique developed to provide a clear and reliable measure of spatial resolution, was used to test sensitivity of the upper and lower lip vermillion, on right and left sides, in a sample of 40 young adults and 40 adults age 66-85. Results indicated that spatial acuity at the lip vermilion declines significantly in old age and that women tend to have better acuity than men. No significant differences were found in acuity between the upper and lower lips or between right and left sides for either age group. Peripheral changes in receptor density and lip tissue composition are suggested as likely causes for the age-related decline.

Perioral muscle activity in young and older adults during speech and nonspeech tasks.

Correlations of EMG activity among paired sites surrounding the lips were examined as a measure of muscle coupling during oral movements. Twenty-tow young women (M = 22 years old) and 22 older women (M = 75 years old) performed lip protrusion, chewing, conversational speech, and reading aloud tasks. Surface EMG was recorded from the right and left sides of both the upper and lower lips during 20 s of task performance. Signals from each site, representing the sum of activity from muscle fibers present in the underlying tissue, were correlated with signals from every other site. Positive correlations were pervasive, but the range of values extended from .96 to -.19. Correlation values tended to be high across the upper lip and across the lower lip, regardless of the task. Other sites (right side, left side, and diagonal pairs) were also highly correlated for the protrusion and chewing tasks, but were less highly correlated for the speech tasks. Younger women showed significantly lower correlation values for speech tasks than older women. Results imply an increase in muscle coupling for speech as an effect of the aging process, perhaps reflecting a reduction in flexibility of fine oral motor control. Limits of the correlation technique and issues concerning speech production ability in old age are discussed.

Reflex responses of lip muscles in young and older women.

The perioral reflex in response to innocuous mechanical stimulation of the lip vermilion was studied in 20 young and 20 older women. Responses to stimuli at the right and left sides of both the upper and lower lips were recorded. Results show significant specificity of response, especially for upper lip sites. Reflex response at the site of stimulation was greatest in amplitude and shortest in latency, followed by response at sites ipsilateral to the site of stimulation. Younger subjects showed greater localizing tendency than older subjects. Stimulation was significantly less likely to produce a reflex response in the older group. When reflex responses did occur, they were significantly lower in amplitude and longer in latency than the responses of the younger group. Nonetheless, reflex responses were common in both groups, with responses at the site of stimulation occurring 78% of the time in older women and 90% of the time in younger women. Every participant showed at least one reflex response to lip stimulation. Results suggest decreasing complexity of synaptic drive to the perioral system in old age but also show that reflexive response does not deteriorate completely, remaining an available element for motor control in normal older women.

Human perioral muscle activation patterns.

Task-dependent human motor organization in the perioral region was examined in eight normal adults who performed oral tasks including lip protrusion, chewing, and speech. Zero phase-lag correlations among EMG signals recorded from quadrants surrounding the lips were calculated in order to determine patterns of motor coupling. Results indicated that the perioral musculature is flexible in output organization. Activity in all quadrants was highly positively correlated during the protrusion task. During the chewing task, correlations were moderate, with a stronger pattern bilaterally across the upper and lower lips. The speech tasks showed lower levels of correlation among the quadrants, but again the pattern was more highly correlated bilaterally than ipsilaterally. Results are compared to studies of oral muscle innervation in humans and animals and also are related to hypotheses of cortical control patterns for oral movement.

Event-related brain potentials preceding speech and nonspeech oral movements of varying complexity.

Cortical preparation for movement is reflected in the readiness potential (RP) waveform preceding voluntary limb movements. In the case of oral movements, the RP may be affected by the complexity or linguistic nature of the tasks. In this experiment, EEG potentials before a nonspeech task (lip pursing), a speech-like task (lip rounding), and single word production were recorded from scalp electrodes placed at the cranial vertex (Cz) and over the left and right motor strips (C3' and C4'). Seven right-handed female subjects produced at least 70 repetitions of the three tasks, in each of five repeated sessions. EEG records were averaged with respect to EMG onset at the lip. The word task, as opposed to the other tasks, was associated with greater negative amplitude in the RP waveform at the vertex site. Differences between the waveforms recorded at the right- and left-hemisphere sites were insignificant. Although intersubject variability was high, individuals had relatively stable patterns of response across sessions. Results suggest that the RP recorded at the vertex site is sensitive to changes in task complexity. The RP did not reflect lateralized activity indicative of hemispheric dominance.

Cerebral averaged potentials preceding oral movement.

The "readiness potential" is an event-related potential that shows increasing negativity at vertex and motor strip scalp recording sites prior to voluntary, unilateral limb movements. Though speech involves movement on both sides of the midline, recent recordings of prespeech potentials suggest a pattern of bilateral activation that lateralizes to the dominant hemisphere just prior to the onset of articulatory movement. To determine whether this pattern of dominant hemisphere activation is present prior to a stereotyped, nonspeech movement of the mouth, the averaged potentials preceding a lip protrusion task were recorded at the cranial vertex and over the right and left motor cortex. Results were compared to potentials preceding a right finger extension task performed by the same subjects. Both the finger and the lip movements were initially preceded by slow negative potentials. Prior to the finger extension task, the negative amplitude became greatest over the left motor cortex, contralateral to the side of movement. Prior to the lip protrusion task, the amplitude of the potential remained even over the right and left motor cortices. The results suggest that, for this nonspeech movement of a midline structure, bilateral cortical control takes place. Control of lip movement is apparently not necessarily a dominant hemisphere function, though dominance may become part of the motor control strategy for more complex movements such as those used during speech.