This investigation was designed to quantify the coordinative organization of mandibular muscles in toddlers during speech and nonspeech behaviors. Seven 15-month-olds were observed during spontaneous production of chewing, sucking, babbling, and speech. Comparison of mandibular coordination across these behaviors revealed that, even for children in the earliest stages of true word production, coordination was quite different from that observed for other behaviors. Production of true words was predominantly characterized by relatively stronger coupling among all mandibular muscles compared with earlier-emerging chewing and sucking. Variegated babbling exhibited stronger coupling than reduplicated babbling, as well as chewing and sucking. The finding of coupled activation among mandibular antagonists during speech paralleled earlier comparisons of adult speech and nonspeech behaviors (Moore, Smith, & Ringel, 1988) and did not support the suggestion that speech coordination emerges from earlier appearing oral motor behaviors. Keywordsspeech; development; motor control; mandible; human A persistent question in our understanding of the coordinative framework of speech production is the relationship of speech to other oral motor behaviors (Moore, Smith, & Ringel, 1988;Ostry, Feltham, & Munhall, 1984;Ostry & Munhall, 1994). Although recent investigations have provided strong support for the existence of separate and distinct mechanisms for speech and nonspeech coordination in adults (Moore et al., 1988), empirical physiologic studies of speech development are lacking. This lack of evidence leaves in doubt the essential foundations of speech motor control.Two lines of reasoning can be taken to address the coordinative framework of speech during the early stages of development. The first draws on mechanisms of pattern generation, which have been directly observed in animals (see Grillner, 1981), as well as dynamical systems theory (e.g., Fentress, 1976;Kent & Hodge, 1990;Thelen & Cooke, 1987;Thelen & Fisher, 1983;Thelen, Skala, & Kelso, 1987; Thelen & Urich, 1991). A dynamic pattern perspective might suggest that speech movements emerge gradually through an interaction of context (i.e., external conditions) with intrinsically generated patterns stemming from the rhythmic movements of sucking, chewing, reduplicated babbling, and variegated babbling. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptAn alternative approach holds that speech develops independent of extant behaviors, emerging as a new and unique motor skill. Support for this position is drawn directly from observations of babbling rhythmicity (see summary by Kent, Mitchell, & Sancier, 1991) and further relies on findings that the coordinative organization of mature speech is distinct from that of any of the postulated precursors (Moore et al., 1988;Ostry & Munhall, 1994). The established orofacial coordination available to children from these behaviors does not appear to be well suited to speech. For example, kinematic and po...

Developmental changes in the coordinative organization of masticatory muscles were examined longitudinally in four children over 49 experimental sessions spanning the age range of 12-48 mo. Electromyographic (EMG) records were obtained for right and left masseter muscles, right and left temporalis muscles, and the anterior belly of the digastric. Two independent analytic processes were employed, one that relied on identification of onset and offset of muscle activation and a second that used pairwise cross-correlational techniques. The results of these two analyses, which were found to be consistent with each other, demonstrated that the basic chewing pattern of reciprocally activated antagonistic muscle groups is established by 12 mo of age. Nevertheless, chewing efficiency appears to be improved through a variety of changes in the chewing pattern throughout early development. Coupling of activity among the jaw elevator muscles was shown to strengthen with maturation, and the synchrony of onset and offset of these muscles also increased. Coactivation of antagonistic muscles decreased significantly with development. This decrease in antagonistic coactivation and increase in synchrony among jaw elevators, and a parallel decrease in EMG burst duration, were taken as evidence of increased chewing efficiency. No significant differences in the frequency of chewing were found across the ages studied. Additional considerations include the appropriateness of this coordinative infrastructure for other developing oromotor skills, such as speech production. It is suggested that the relatively fixed coordinative framework for chewing exhibited by these children would not be suitable for adaptation to speech movements, which have been shown to rely on a much more variable and adjustable coordinative organization.

Neuromuscular electrical stimulation (NMES) therapy has been proposed as a treatment option for pharyngeal dysphagia. However, little is known about the effects, if any, that NMES has on specific biomechanical aspects of the pharyngeal swallow. The purpose of this study was to determine if two weeks of NMES applied to the submental muscles increased myoelectric activity. Ten age- and gender-matched subjects participated, and eight completed the protocol. Treatment was delivered using an AB or BA design. No treatment was given during the A condition. Subjects received ten 1-h NMES treatments during the B condition. Results indicated that seven of eight subjects exhibited no significant gains in myoelectric activity of the submental muscles following NMES. Therefore, the benefit of NMES to the submental muscles with the goal of improving the pharyngeal swallow is not supported. Additional research investigating duration of treatment as well as frequency and amplitude modulation of NMES is needed to determine if, how, and why NMES applied to the submental muscles affects the biomechanical aspects of both the normal and disordered pharyngeal swallow.

Research has shown that swallowing in adults is affected by bolus consistency. Little is known, however, regarding the effect of bolus consistency on swallowing in children. Electromyographic (EMG) data from typically developing five- and eight-year-old-children and adults were obtained from the following muscles as they swallowed boluses of different consistencies: (1) right upper lip, (2) right lower lip, (3) submental, and (4) laryngeal strap. Signal analyses included calculating EMG onset and offset and average EMG amplitude of muscle activity during swallowing. Findings revealed that by five years of age, children employ adultlike control strategies during swallowing: significant differences in duration and magnitude of muscle activity resulted as a function of bolus consistency. General observations revealed, however, that swallowing in children is characterized by muscle activity that is shorter in duration. Similarities and differences in the biomechanics of swallowing between children and adults are important to consider during clinical evaluations and treatment of children with dysphagia.