Individual variation in bilingual vocabulary in preschoolers with developmental language disorder

Background: It is unclear how speech production, selective attention, and phonological working memory are related to first- (L1) and second-language (L2) vocabularies in bilingual preschoolers with Developmental Language Disorder (DLD). Aims: To study individual variation in vocabularies in DLD bilingual preschoolers by (1) comparing them to typically developing (TD) bilingual, and TD and DLD monolingual peers; (2) differentially predicting L2 vocabulary; and (3) identifying and characterizing bilinguals' L1/L2 vocabulary profiles. Methods: We measured the selective attention, working memory, and L1 Turkish/Polish (where applicable) and L1/L2 Dutch speech and vocabulary abilities of 31 DLD bilingual, 37 TD bilingual, and 61 DLD and 54 TD Dutch monolingual three-to-five year-olds. Results: DLD bilinguals scored lower than TD bilinguals and TD/DLD monolinguals on all measures, except L2 vocabulary, where all bilinguals underperformed all monolinguals. Selective attention predicted Dutch vocabulary across groups. Three bilingual vocabulary profiles emerged: DLD bilinguals were less likely to be L1 dominant, TD/DLD bilinguals with better attention more often had a Balanced high L1/L2 profile, while those with poorer selective attention and L1 speech tended to be L2 dominant. Conclusions: These findings highlight the roles of L1 speech and selective attention, rather than L2 speech and working memory, in understanding bilingual vocabulary variation among DLD preschoolers.