Vocal output in preterm infants.

Data on vocal output of 51 preterm infants and 16 term infants were obtained during naturalistic home observations at 1, 3, and 8 months; during the administration of a preference-for-novelty paradigm in the laboratory at 8 months; and by the administration of the Gesell Developmental Schedules at 9 months. Preterm and term infant groups were found to show both similarities and differences: both groups vocalized a similar amount in the preference-for-novelty situation; both groups earned similar scores on the language subtest of the Gesell; both groups increased the percentage of awake time they spent in nondistress vocalization from 1 to 8 months. Term infants showed an earlier increase than did preterm infants: term infants significantly increased during the 1-3 month period, whereas preterm infants only increased significantly during the 3-8 month period. The developmental differences suggest a link between vocal output and perinatal conditions in that caregiver behavior was not found to be different among groups. Within the preterm groups, some relationships were found between vocal output and later test performance: infants who vocalized more during mutual gazing with the mother earned significantly higher scores on the language subtest of the Gesell.