Bilingual Minds

The regular use of two languages by bilingual individuals has been shown to have a broad impact on language and cognitive functioning. In this monograph, we consider four aspects of this influence. In the first section, we examine differences between monolinguals and bilinguals in children’s acquisition of language and adults’ linguistic processing, particularly in terms of lexical retrieval. Children learning two languages from birth follow the same milestones for language acquisition as monolinguals do (first words, first use of grammar) but may use different strategies for language acquisition, and they generally have a smaller vocabulary in each language than do monolingual children learning only a single language. Adult bilinguals typically take longer to retrieve individual words than monolinguals do, and they generate fewer words when asked to satisfy a constraint such as category membership or initial letter. In the second section, we consider the impact of bilingualism on nonverbal cognitive processing in both children and adults. The primary effect in this case is the enhancement of executive control functions in bilinguals. On tasks that require inhibition of distracting information, switching between tasks, or holding information in mind while performing a task, bilinguals of all ages outperform comparable monolinguals. A plausible reason is that bilinguals recruit control processes to manage their ongoing linguistic performance and that these control processes become enhanced for other unrelated aspects of cognitive processing. Preliminary evidence also suggests that the executive control advantage may even mitigate cognitive decline in older age and contribute to cognitive reserve, which in turn may postpone Alzheimer’s disease. In the third section, we describe the brain networks that are responsible for language processing in bilinguals and demonstrate their involvement in nonverbal executive control for bilinguals. We begin by reviewing neuroimaging research that identifies the networks used for various nonverbal executive control tasks in the literature. These networks are used as a reference point to interpret the way in which bilinguals perform both verbal and nonverbal control tasks. The results show that bilinguals manage attention to their two language systems using the same networks that are used by monolinguals performing nonverbal tasks. In the fourth section, we discuss the special circumstances that surround the referral of bilingual children (e.g., language delays) and adults (e.g., stroke) for clinical intervention. These referrals are typically based on standardized assessments that use normative data from monolingual populations, such as vocabulary size and lexical retrieval. As we have seen, however, these measures are often different for bilinguals, both for children and adults. We discuss the implications of these linguistic differences for standardized test performance and clinical approaches. We conclude by considering some questions that have important public policy implications. What are the pros and cons of French or Spanish immersion educational programs, for example? Also, if bilingualism confers advantages in certain respects, how about three languages—do the benefits increase? In the healthcare field, how can current knowledge help in the treatment of bilingual aphasia patients following stroke? Given the recent increase in bilingualism as a research topic, answers to these and other related questions should be available in the near future.