Estimations of Child Linguistic Productivity Controlling for Vocabulary and Sample Size

Children's use of present tense suffixes is less productive than that of their parents, after correcting for sample size and lexical knowledge, according to a recently established approach for the study of inflectional productivity in Spanish speech samples (Aguado-Orea & Pine, 2015). This article expands on this technique by providing precise estimates of early grammatical productivity through systematic random sampling and allowing for developmental assessment. Two cross-linguistic comparisons are given in the results of this study. Two Spanish-speaking children and their parents are compared with four English-speaking children and their parents. The second comparison examines potential differences in productivity throughout developmental stages using the same six children's speech. The findings indicate that Spanish-acquiring children are less productive than their parents while utilising the paradigm under study, but that productivity levels increase over time. In contrast, the English-speaking children's morphosyntactic production mirrors that of their parents. Although the primary focus of this research is methodological, these findings have consequences for theoretical theories arguing either rule abstraction or a restricted generalisation of early exemplars.

When previous analyses of grammatical productivity have looked at the spontaneous speech of children, they have been mainly focused on the error rates committed by children. Some analyses of productivity looking at richly inflected languages have been run too, but they have not been matched with other languages like English. The present study, with a strong methodological focus, aims at presenting the results of a new technique for estimating the creativity (and triteness) in the possible combinations of subject agreement in English and Spanish. The main objectives are 1) to examine to what extent the early use of language by children is less productive than the adult one, 2) to see if children’s grammatical productivity increase developmentally for the use of subject verb agreement in English and Spanish, and, 3) to explore the potential differences in productivity observed across languages. The article expects to provide the community of researchers interested in language acquisition with a relatively simple tool allowing for controlled analyses of grammatical productivity, fully available online.