How strong is the relationship between caregiver speech and language development? A meta-analysis.

A growing body of research has found that talking to young children is positively associated with language outcomes. However, there is tremendous heterogeneity in the design of these studies, which could potentially affect the strength and reliability of this association. The present meta-analysis, comprising 4760 participants across 71 studies, goes beyond prior research by including: 1) more recent studies, 2) non-English-speaking populations, 3) more fine-grained categorization of measures of input, 4) additional moderators, and 5) a multilevel model design allowing us to consider multiple effect sizes per study.

Disentangling the roles of age and knowledge in early language acquisition: A fine-grained analysis of the vocabularies of infant and child language learners.

The words that children learn change over time in predictable ways. The first words that infants acquire are generally ones that are both frequent and highly imageable. Older infants also learn words that are more abstract and some that are less common.

It's All in the Interaction: Early Acquired Words Are Both Frequent and Highly Imageable.

Prior studies have found that children are more likely to learn words that are frequent in the input and highly imageable. Many theories of word learning, however, predict that these variables should interact, particularly early in development: frequency of a form is of little use if you cannot infer its meaning, and a concrete word cannot be acquired if you never hear it. The present study explores this interaction, how it changes over time and its relationship to syntactic category effects in children acquiring American English.

The effects of maternal input on language in the absence of genetic confounds: Vocabulary development in internationally adopted children.

Previous studies have found correlations between parent input and child language outcomes, providing prima facie evidence for a causal relation. However, this could also reflect the effects of shared genes. The present study removed this genetic confound by measuring English vocabulary growth in 29 preschool-aged children (21 girls) aged 31-73 months and 17 infants (all girls) aged 15-32 months adopted from China and Eastern Europe and comparing it to speech produced by their adoptive mothers.