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.