Vocal fundamental frequency characteristics of infant hunger cries: birth to 12 months.

The vocal fundamental frequency (Fo) characteristics of four infants' hunger cries are reported. The infants were audio recorded at monthly intervals during the first year of life. In general, each infant's Fo increased across the one-year period. The increase in Fo was attributed to the transition from early reflexive crying to intentional vocalization behavior, rather than anatomical and physiological growth influences. Discussion focuses on the regulation of infant crying behavior across the first year of life, as well as the diagnostic implications of these findings.