Relative kinematics of the rib cage and abdomen during speech and nonspeech behaviors of 15-month-old children.

Speech motor control emerges in the neurophysiologic context of widely distributed, powerful coordinative mechanisms, including those mediating respiratory function. It is unknown, however, whether developing children are able to exploit the capabilities of neural circuits controlling homeostasis for the production of speech and voice. Speech and rest breathing were investigated in eleven 15-month-old children using inductance plethysmography (Respitrace). Rib cage and abdominal kinematics were studied using a time-varying correlational index of thoracoabdominal coupling (i.e., reflecting the synchrony of movement of the rib cage and abdomen) as well as simple classification of the moment-to-moment kinematic relationship of these two functional components (i.e., concurrent expansion or compression, or oppositional movement). Results revealed markedly different patterns of movement for rest breathing and speech breathing, although within types of vocalization (nonspeech vocalization, babbling, true word production) no differences were apparent. Whereas rest breathing was characterized by tight coupling of rib cage and abdominal movement (average correlation coefficients usually exceeded .90), speech breathing exhibited weak coupling (the correlation coefficient ranged widely, but averaged about .60). Furthermore, speech production by these toddlers included the occurrence of both rib cage and abdominal paradoxing, which are observed infrequently in adult speakers. These results fail to support the suggestion that speech emerges from the extant coordinative organization of rest breathing. Rather, even in its earliest stages breathing for speech and voice exhibits kinematic properties distinct from those of other observed behaviors.