Semi-Occluded Vocal Tract in Infant Cry

Objectives: The objective is to show that a semi-occlusion in the vocal tract is innately driven by maximum power transfer from the sound source to the vocal tract. In infant cry, a vocal tract resistance for source-filter impedance matching is produced in the pharyngeal region, often with a secondary aperiodic sound source at the velum.

Methods: The approach was computational. An infant vocal tract was constructed digitally with multiple sections from the trachea to the lips. A simplified Navier-Stokes (Titze, Palaparthi, and Smith, 2014) was used to calculate fluid transport and acoustic wave propagation, including radiation from the lips.

Results: Computational results verify that infant cry is characterized by high intensity, on the order of 99 – 110 dB(A) at 30 cm from the mouth. For a loud cry, the vibration is often described as chaotic in the language of nonlinear dynamics. It is perceived as grating, an added factor for demanding attention from a caregiver.

Conclusions: Infants cry with lung pressures equal to or greater than adults when calling or shouting. Airflow resistances are on the order of 20-30 times greater than in adults. A pharyngeal semi-occlusion is used for maximum power transfer from the glottis to the vocal tract.