The controversy over whether bilingualism leads to reliable changes in cognitive and brain functions shows no sign of abating. Regarding behavioral evidence for cognitive performance, evidence from apparently similar studies that shows both better outcomes for bilinguals and no group differences continue to be reported. Notably, there are essentially no studies showing better performance by monolinguals. Regarding imaging studies, analyses of functional recruitment during task performance typically show different patterns for monolingual and bilinguals, a difference that cannot be interpreted as being “better” or “worse”, but analyses of brain structure, especially in older adults, sometimes show more preserved structure for bilinguals and sometimes the opposite, namely, more preserved structure for monolinguals. How can these contradictory findings be reconciled?

I will begin by reviewing the evidence for effects of bilingualism across the lifespan, pointing to areas of greatest and least consistency. The clearest evidence comes from the endpoints of the lifespan, namely, infants and older adults. What is common to the processing recruited by preverbal infants and older adults with cognitive decline that might shed light on changes in bilingual processing across the lifespan? My suggestion is that bilingual environments and bilingual language use modify the attentional demands of all language and cognitive processing, and that the constant exposure to these demands leads to an adaptation in selective attention networks. The outcome of this adaptation is to build resilience across the lifespan, culminating in cognitive reserve in older age. These ideas will be developed and applied to the range of available evidence.