UC San Diego

The acquisition of a second language often occurs during early childhood, a period of dynamic change in cognitive, language, and brain development.  This thesis examined the contribution of two important factors in bilingualism, language experience and SES, in association with individual differences in language skills, executive function, and white matter maturation in bilingual children.  Language skills in both English and Spanish were measured, including vocabulary, verbal fluency, and spoken narrative skills.  Executive function measures for response inhibition, inhibitory control, and cognitive flexibility were also examined. While bilinguals had lower receptive English vocabulary than the monolingual children, within the bilingual group, language experience was a contributing factor to language outcomes in both languages.  When both SES and language experience were entered as predictors of the language measures, SES was only significant for English expressive vocabulary scores in bilinguals.  Bilingual children underperformed on executive function tasks compared to the monolingual children, although, SES accounted for group differences in cognitive flexibility (though not inhibitory control) performance.  The group comparisons revealed an interaction effect of language group by SES for response inhibition, such that among the bilingual children, there was a negative association between SES and performance, but not for the monolingual children.  Within the bilingual group, language experience and SES both were contributing factors to individual differences in executive function performance, while differing patterns of associations for executive function measures emerged.  In addition, white matter maturation was compared in bilingual children to monolingual children in three white matter fiber tracts, the inferior fronto-occipital fasciculus (IFOF), the superior longitudinal fasciculus (SLF), and the anterior cingulum.  Monolingual children showed greater white matter maturation in the SLF compared to the bilingual group, independent of SES.  Post-hoc analysis revealed group differences in white matter maturation in the separate segments of the IFOF, such that monolinguals had more mature values on white matter measures in the anterior and middle IFOF, while bilinguals had more mature values in the posterior IFOF.  Within the bilingual group, language experience was related to more mature white matter characteristics in the anterior cingulum, a brain region thought to support language control in bilinguals.