What makes a word easy to acquire? The effects of word class, frequency, imageability and phonological neighbourhood density on lexical development

This article analyses how a set of psycholinguistic factors may account for children's lexical development. Age of acquisition is compared to a measure of lexical development based on vocabulary size rather than age, and robust regression models are used to assess the individual and joint effects of word class, frequency, imageability and phonological neighbourhood density on Norwegian children's early lexical development. The Norwegian Communicative Development Inventories (CDI) norms were used to calculate each CDI word's age of acquisition and vocabulary size of acquisition. Lexical properties were downloaded from the lexical database Norwegian Words, supplemented with data on frequency in adult and child-directed speech. Age of acquisition correlated highly with vocabulary size of acquisition, but the new measure was more evenly distributed and more sensitive to lexical effects. Frequency in childdirected speech was the most important predictor of lexical development, followed by imageability, which seems to account for the dominance of nominals over predicates in Norwegian.