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Purpose: The ontogeny of mandibular control is important for understanding the general neurophysiologic development for speech and alimentary behaviors. Prior investigations suggest that mandibular control is organized distinctively across speech and nonspeech tasks in 15-month-olds and adults and that, with development, these extant forms of motor control primarily undergo refinement and rescaling. The present investigation was designed to evaluate whether these coordinative infrastructures for alimentary behaviors and speech are evident during the earliest period of their co-occurrence.
Method: Electromyographic (EMG) signals were obtained from the mandibular muscle groups of 15 typically developing 9-month-old children during sucking, chewing, and speech.
Results: Unlike prior investigations of 12- and 15-month-olds and adults, 9-month-olds’ analyses of peak correlations among agonist and antagonist comparisons of mandibular EMG data revealed weak coupling during sucking, chewing, and babble; associated lag values for antagonist muscle groups indicated greater synchrony during alimentary behaviors and less synchrony during babble. Unlike the speech data of 15-month-olds, 9-month-olds exhibited consistent results across speech subtasks.
Conclusion: These findings were consistent with previous results in which mandibular coordination across behaviors was more variable for younger age groups, whereas the essential organization of each behavior closely reflected that seen in older infants and adults.