Parental verbal responsiveness to infant vocalizations from 9 to 14 months of age

Parental communication styles and language usage may undergo changes during the course of child development, exhibiting variations across language backgrounds and cultures. This study aimed to explore how infant-parent interactions within Korean-speaking environments evolve over time through meticulous coding of day-long home audio recordings. The study examined whether the ratio and types of parental verbal responses vary based on infants' age and vocalization types. A total of 16 infants and their parents participated in all-day home recordings using the Language Environment Analysis (LENA) system. The recordings were conducted in two rounds per family when the infants were aged 9-11 months and 12-14 months, with a three-month gap between each round. The frequency and types of infant vocalizations were analyzed and the contingency and types of parental verbal responsiveness were determined based on semantic and phonetic connection, as well as temporal appropriateness. The results showed that parents did not verbally respond to approximately 50 % of the infant vocalizations in the natural home environment. However, parents' lack of verbal responses decreased significantly, and their contingent responses increased significantly with infant age. Parents were also not selectively responsive to infants' canonical vocalizations over non-canonical vocalizations. Nevertheless, parents demonstrated a higher frequency of responses that were not only linguistically meaningful but also socially appropriate and contextually relevant to infants' vocalizations as infants developed, which may play a significant role in scaffolding speech and language development.