1. Language-based interactions between children 18 to 24 months of age and adults predicted intelligence quotient (IQ), verbal comprehension, and expressive and receptive language skills at 9 to 13 years old.
2. There were no significant relationships between language-based interactions and subsequent IQ or language skills in other age groups.
Evidence Rating Level: 2 (Good)
Study Rundown: Previous research has shown that a child’s environment during critical language development periods has effects on developmental outcomes through early elementary school. Less is known about longer-term effects of early language environments. In this prospective cohort study, researchers used daylong audio recordings of children 2 to 36 months old and their families to quantify language interactions and examine the relationship between these interactions and IQ and language outcomes at 10-year follow-up. Higher amounts of conversational turn-taking between children aged 18 to 24 months and others in their environment predicted IQ, verbal comprehension, and expressive and receptive language skills at follow-up. This effect persisted after controlling for socioeconomic status (SES). There were no significant relationships observed outside the 18 to 24 months age group.
These findings are limited by the study’s monolingual English sample, which reduces generalizability. Furthermore, causality cannot be established and other factors may primarily account for differences in IQ and language skills. Nonetheless, the study is strengthened by its long follow-up and thorough characterization of language interactions. For physicians, these findings highlight the importance of working with parents and guardians to foster interactive language environments, especially for children during critical periods of language development.
In-Depth [prospective cohort]: Researchers used Language Environment Analysis (LENA) software to record and quantify child vocalization, turn-taking interactions, and adult word exposure during audio recordings of 146 families with children 2 to 36 months old. Families were recorded for 12 hours monthly over 6 months. Child language skills were assessed with the Preschool Language Scale and Receptive-Expressive Emergent Language Test. Follow-up evaluations were conducted at age 9 to 14 years using the Wechsler Intelligence Scale for Children, Peabody Picture Vocabulary Test, and Expressive Vocabulary Test. Pearson correlations were calculated to examine relationships between language interactions during audio recording and later IQ and language outcomes during follow-up, then recalculated adjusting for SES and repeated by age subgroups.
Conversational turn counts at 18 to 24 months old accounted for 14% of the variance in IQ (r = 0.37; [95% confidence interval (CI): 0.08 to 0.60]; R2 = 0.14; p = .01) and 27% of the variance in Verbal Comprehension Index (r = 0.52; [95% (CI): 0.26 to 0.71]; R2 = 0.27; p < .001) at 10-year follow-up after adjusting for SES. Adult word count was similarly predictive of IQ and language skills, but this relationship was weakened after controlling for SES. No significant relationships were observed outside of the 18 to 24 months age group.
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