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AbstractInterventions focused on the home language environment have been shown to improve a number of child language outcomes in the first years of life. However, data on the longer‐term effects of the intervention are still somewhat limited. The current study examines child vocabulary and complex speech outcomes (N = 59) during the year following completion of a parent‐coaching intervention, which was previously found to increase the quantity of parent‐child conversational turns and to improve child language outcomes through 18 months of age. Measures of parental language input, child speech output, and parent‐child conversational turn‐taking were manually coded from naturalistic home recordings (Language Environment Analysis System, LENA) at regular 4‐month intervals when children were 6‐ to 24‐months old. Child language skills were assessed using the MacArthur–Bates Communicative Development Inventory (CDI) at four time‐points following the final intervention session (at 18, 24, 27, and 30 months). Vocabulary size and growth from 18 to 30 months was greater in the intervention group, even after accounting for differences in child language ability during the intervention period. The intervention group also scored higher on measures of speech length and grammatical complexity, and these effects were mediated by 18‐month vocabulary. Intervention was associated with increased parent‐child conversational turn‐taking in home recordings at 14 months, and mediation analysis suggested that 14‐month conversational turn‐taking accounted for intervention‐related differences in subsequent vocabulary. Together, the results suggest enduring, positive effects of parental language intervention and underscore the importance of interactive, conversational language experience during the first 2 years of life.Research Highlights
Parent coaching was provided as part of a home language intervention when children were 6–18 months of age.
Naturalistic home language recordings showed increased parent‐child conversational turn‐taking in the intervention group at 14 months of age.
Measures of productive vocabulary and complex speech indicated more advanced expressive language skills in the intervention group through 30 months of age, a full year after the final intervention session.
Conversational turn‐taking at 14 months predicted subsequent child vocabulary and accounted for differences in vocabulary size across the intervention and control groups.

AbstractThe development of skills related to executive function (EF) in infancy, including their emergence, underlying neural mechanisms, and interconnections to other cognitive skills, is an area of increasing research interest. Here, we report on findings from a multidimensional dataset demonstrating that infants' behavioral performance on a flexible learning task improved across development and that the task performance is highly correlated with both neural structure and neural function. The flexible learning task probed infants' ability to learn two different associations, concurrently, over 16 trials, requiring multiple skills relevant to EF. We examined infants' neural structure by measuring myelin density in the brain, using a novel macromolecular proton fraction (MPF) mapping method. We further examined an important neural function of speech processing by characterizing the mismatch response (MMR) to speech contrasts using magnetoencephalography (MEG). All measurements were performed longitudinally in monolingual English‐learning infants at 7‐ and 11‐months of age. At the group level, 11‐month‐olds, but not 7‐month‐olds, demonstrated evidence of learning both associations in the behavioral task. Myelin density in the prefrontal region at 7 months of age was found to be highly predictive of behavioral task performance at 11 months of age, suggesting that myelination may support the development of these skills. Furthermore, a machine‐learning regression analysis revealed that individual differences in the behavioral task are predicted by concurrent neural speech processing at both ages, suggesting that these skills do not develop in isolation. Together, these cross‐modality results revealed novel insights into EF‐related skills.Highlight
Monolingual infants demonstrated flexible learning on a task requiring executive function skills at 11 months, but not at 7 months.
Infants' myelin density at 7 months is highly predictive of their behavioral performance in the flexible learning task at 11 months of age.
Individual differences in the flexible learning task performance are also correlated with concurrent neural processing of speech at both ages.