LangDiv: Hypotheses about the sources of bilingual resilience over the lifespan

The idea that learning and using two languages might interfere with a child's language development or cause confusion is a long-standing myth. Research has demonstrated that bilingualism, exposure to and use of two languages, causes beneficial changes in the brain that can be seen across the lifespan, from infancy and into old age. A bilingual person's two languages are always active, requiring a continual process of juggling to speak the intended language but also the ability to switch between languages at ease. After a lifetime of engaging these processes older bilingual adults tend to be protected from some of the cognitive decline that marks both healthy and pathological aging. Older bilingual adults appear to preserve better cognitive function for longer than older monolingual adults. This project conducts a series of experiments that explore the reasons for this benefit of bilingualism. The experiments are oriented around the finding that, while bilingualism appears to delay the onset of dementia symptoms, when bilinguals finally develop symptoms they are often not able to use their second language. Two explanations have been proposed to explain the loss of the second language. The first explanation attributes the loss to a decline in inhibitory control, the process that controls the ability to switch between languages. The second explanation involves a decline in the relationships between words and what they mean. This project tests these alternatives by comparing the performance on language tasks that engage these different processes. Network analysis is used to measure how connected utterances from language production tasks are and data from word production tasks measure cognitive control and language regulation. This project develops a general protocol that will identify patterns of language and cognitive change with aging. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.