A broadened estimate of syntactic and lexical ability from the MCDI

A critical question in the study of language development is to understand lexical and syntactic acquisition. Functional and content words are acquired and processed differently, demonstrated in deaf acquisition and electroencephalography work. As measured through the comprehension and production of closed-class words, syntactic ability emerges at roughly the 400-word mark. However, a significant proportion of the developmental work uses a coarse combination of functional and content words on the MacArthur-Bates Communicative Development Inventory (MCDI). Using the MCDI Wordbank database, we implemented a factor analytic approach to elucidate lexical and syntactic development from the Words and Sentences (WS) form that involves both functional words and the explicit categorizations. Although the Words and Gestures (WG) form did not share the factor structure, common WG/WS elements recapitulate the expected age-related changes. This simple parsing of the MCDI may prove simple, yet fruitful in subsequent investigation.