Noisy but effective: crying across the first 3 months of life

To evaluate the developmental occurrence of subharmonic (SH) and noise (N) phenomena and to quantify their extent in the spontaneous cries of healthy infants across the first 3 months.

Populational prospective study.

Spontaneous elicited cries from 20 infants (10 male) were repeatedly recorded across the first 3 months of life.

Frequency spectra and waveforms were used to identify the occurrence of SH and N and to measure the percentage of their combined occurrence in overall monthly crying behavior (expressed as a quantitative noise index [NI]).

SH and N episodes were prevalent in the cries of young infants during the first 2 months, being present in more than 50% of the recorded cries. A developmental trend was evident in NI with a significant decrease across the 3-month period. A corresponding significant increase in mean duration of single cries was observed during the same period.

SH and phonatory noise are regularly occurring phenomena in healthy infant crying because of the characteristics of pediatric larynx anatomy and neurophysiological control mechanisms underlying cry production. The reduction in NI appears to correspond with the development of an infant's crying complexity. The utility of NI as a metric of cry phonatory behavior should next be validated on infant groups with known or suspected health problems.