On the Development of Breathing and Vocalization in a Prelinguistic Child: A Case Study.

Introduction: While breathing is essential for infant speech development, it has neither been extensively studied empirically nor been included in theories of speech acquisition. In this brief report, we explored the co-development of respiratory and vocal control longitudinally in an infant from 7;15 to 9;15 months of age. We focused on this period because it usually coincides with the emergence of canonical babbling which may go hand in hand with changes in infants' laryngeal-oral-respiratory coordination.

Methods: Infant-mother interactions were recorded biweekly in the laboratory. Infant breathing and acoustics were recorded using Inductance plethysmography and a microphone, while video data were recorded with two camcorders. All vocalizations were acoustically annotated as well as their underlying inhalation and exhalation phases. Vocalizations alone, vocalizations occurring with body motions and/or acoustic overlap were labeled and their frequency calculated. We also calculated the percentage of inhalation duration with respect to the overall breath cycle duration. Finally, we extracted examples of breathing in relation to f0 and intensity.

Results: Vocalization occurred only in 37% on their own, 63% were produced with motion and/or overlap with other noise sources. Respiratory cycles became more asymmetric with longer exhalation phases over developmental time. The relation between phonation and respiration changed over time, with repetitive phonation often occurring during inspiration at 7;15 months to expiration at 9;15 months.

Conclusion: While our brief report relies on the data of one baby only, this longitudinal study provides insights on the developing relation between respiration and phonation during the first year of life. If confirmed in a larger sample, these preliminary findings suggest that respiration is a fundamental component of language development and should be considered an integral part of the speech production system.