Japanese provides a valuable contrast for crosslinguistic studies of noun and verb dominance in early child language, and the effect of input on the early lexicon. In this study, 31 Japanese children between 1;0 and 2;0 and their caregivers were recorded in two contexts: joint bookreading and play with toys. Context had the largest effect, as nouns were much more frequent in the book context. Noun dominance was constant across development in the book context, but in the toy context there was a shift away as children developed from single words through the presyntactic stage to the syntactic stage. Caregiver language was verb dominant in a number of respects across development in the toy context, and thus was not closely related to child lexical balance. We conclude that in early lexical development, all children have a conceptual disposition to learn nouns. With vocabulary growth and the emergence of grammar, the proportion of verbs increases substantially, and at this stage properties of the input language may influence development.

This study compared the sequential structure of mother-child conversation during joint picture book reading in Japanese and American dyads with children between 12 and 27 months. Although there were commonalities such as increased maternal elaborative information-asking in response to children's labelling with children's vocabulary growth, there were substantial differences. Japanese children produced labelling following maternal labelling more than American children, while American children produced labelling following information-asking more than Japanese children. Japanese mothers responded to children's labelling with interpersonal utterances more than American mothers, while American mothers responded to labelling with elaborative informationasking more than Japanese mothers. Interaction in American dyads generally followed an instruction model, while interaction in Japanese dyads reflected aspects of an osmosis model.

This study extended the research on the scaffolding provided by mothers while reading picture books with their children from a focus on conversational styles related to labeling to a focus on those related to agents and actions to clarify the process by which language develops from the one-word to the syntactic stage. We clarified whether mothers decreased the degree of scaffolding in their initiation of conversations, in the responses to their children’s utterances, and in the choice of referential ranges of their utterances. We also investigated whether maternal conversational styles contributed to the development of their children’s vocabularies. Eighteen pairs of Japanese mothers and their children were longitudinally observed when the children were 20 and 27 months of age. The pairs were given a picture book depicting 24 animals engaged in everyday behavior. The mothers shifted their approach in the initiation of conversation from providing to requesting information as a function of their children’s age. The proportion of maternal elaborative information-seeking responses was positively correlated with the size of their children’s productive vocabulary. In terms of referential choices, mothers broadened the range of their references as their children aged. In terms of the contribution of maternal conversational styles to children’s vocabulary development, the use of a maternal elaborative information-seeking style when the children were 20 months of age predicted the size of the children’s productive vocabulary at 27 months. These results indicate that mothers decrease the degree of scaffolding by introducing more complex information into the conversations and transferring the role of actively producing information to their children by requesting information as their children develop. The results also indicate that these conversational styles promote the development of children’s vocabularies during the transition from the one-word to the syntactic stage.

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