Acoustical development of the human baby cry: Anatomical and social factors

We investigated the acoustical development of the human baby cry based on our two-stage hypothesis, which holds that two distinct factors affect the development of the baby cry. First, humans possess the cortico-bulbar pathway connecting the face motor cortex and the medullary respiratory and vocal centers. This pathway is absent in nonhuman primates and other mammals. We postulate that the myelinization of this pathway would change the acoustic characteristics of the baby cry. Second, after neuroanatomical maturation enabled variable cry patterns, the social relationships with caregivers should differentiate the acoustical patterns of the baby cry. This should lead to family-specific cry patterns. To test the two-stage hypothesis, we recorded ten newborn babies until they were 1 year old. In all babies, the cry pattern was very simple up to 2 weeks, while after 1 month, the pattern became temporally and spectrally complex, suggesting neuroanatomical changes. At three months, we asked the mothers to classify the cries of their own babies into three categories: sleepy, hungry, and wet diaper. There were no acoustic patterns common to their classifications, suggesting that baby cry semantics are family-specific. These results support our two-stage hypothesis of cry development. [Work supported by JST and JSPS.]