To determine the sound environment of preterm infants cared for in the NICU and to test the hypothesis that infants exposed to more adult language will make more vocalizations.


This was a prospective cohort study of 36 infants who had a birth weight of ≤1250 g. Sixteen-hour recordings of the infant sound environment were made in the NICU from a digital language processor at 32 and 36 weeks' postmenstrual age. Adult word counts, infant vocalizations, and conversational turns were analyzed.


Infant vocalizations are present as early as 32 weeks. Both adult word counts per hour and infant vocalizations per hour increase significantly between 32 and 36 weeks. Infant exposure to language as a percentage of time was small but increased significantly. When a parent was present, infants had significantly more conversational turns per hour than when a parent was not present at both 32 and 36 weeks (P < .0001).


Preterm infants begin to make vocalizations at least 8 weeks before their projected due date and significantly increase their number of vocalizations over time. Although infant exposure to language increased over time, adult language accounted for only a small percentage of the sounds to which an infant is exposed in the NICU. Exposure to parental talk was a significantly stronger predictor of infant vocalizations at 32 weeks and conversational turns at 32 and 36 weeks than language from other adults. These findings highlight the powerful impact that parent talk has on the appearance and increment of vocalizations in preterm infants in the NICU.

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