Individual variation in bilingual vocabulary in preschoolers with developmental language disorder

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).

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.

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.

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.

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.