Experience, aptitude and individual differences in native language ultimate attainment

Several recent studies have demonstrated that some native speakers do not fully master some fairly basic grammatical constructions of their language, thus challenging the widely-held assumption that all native speakers converge on the same grammar. This study investigates the extent of individual differences in adult native speakers' knowledge of a range of constructions as well as vocabulary size and collocational knowledge, and explores the relationship between these three aspects of linguistic knowledge and four nonlinguistic predictors: nonverbal IQ, language aptitude, print exposure and education. Individual differences in grammatical attainment were comparable to those observed for vocabulary and collocations; furthermore, performance on tests assessing speakers' knowledge of these three aspects of language was correlated (rs from 0.38 to 0.57). Two of the nonlinguistic measures, print exposure and education, were found to contribute to variance in all three language tests, albeit to different extents. In addition, nonverbal IQ was found to be relevant for grammar and vocabulary, and language aptitude for grammar. These findings are broadly compatible with usage-based models of language and problematic for modular theories.