Bialystock has shown that bilinguals do better at tests that require multitasking, including ones that simulated driving and talking on a phone.
"Make no mistake: Everybody is worse," Bialystock said, "but the bilinguals were less worse."
Bialystock's studies focused on people who were truly bilingual. The longer people have spoken multiple languages, the greater the cognitive effects. There are even benefits when languages were taken up at later ages. "We have not seen a cutoff," she said.
Bilingualism comes with some cost, Bialystock and Costa agreed.
"For bilinguals, there are a couple of milliseconds before you can target the right word in the right language. Bilinguals have more 'tip-of-the-tongue' problems," Bialystock said.
"Bilingual children have on average a smaller vocabulary in each of their languages than monolingual children," she added. "There is a smaller vocabulary in each language, but they probably know more words altogether."
But having improved executive functioning, Bialystock argues, is more important than small differences in vocabulary or millisecond lags in word retrieval.