Receptive and expressive language ability differentially support symbolic understanding over time: Picture comprehension in late talking and typically developing children.

Symbols are a hallmark of human communication, and a key question is how children's emerging language skills relate to their ability to comprehend symbols. In particular, receptive and expressive vocabulary may have related, but distinct, roles across early development. In a longitudinal study of late talking (LT) and typically developing (TD) children, we differentiated the extent to which expressive and receptive language skills predicted symbolic understanding as reflected in picture comprehension and how language skills inter-related with social skills. LT and TD children were tested on a picture comprehension task that manipulated the availability of verbal labels at 2.0-2.4 years and 3.5-3.9 years of age. Although all children improved in accuracy over time as expected, TD children exhibited an advantage over LT children, despite both groups using verbal labels to inform their mapping of picture-object relationships. Receptive and expressive vocabulary also differed in their contribution at different ages; receptive vocabulary predicted performance at ∼2.0 years of age, and expressive vocabulary predicted performance at ∼3.5 years of age. Task performance at 3.5 years was predicted by earlier receptive vocabulary, but this effect was largely mediated by concurrent expressive vocabulary. Social ability across the whole sample at ∼2.0 years also predicted and mediated the effect of receptive vocabulary on concurrent task performance. These findings suggest that LT children may have delays in developing picture comprehension over time and also that social ability and language skills may differentially relate to symbolic understanding at key moments across development.