Research into how multilingual people juggle more than one language in their minds is complex and sometimes counterintuitive. It turns out that when a multilingual person wants to speak, the languages they know can be active at the same time, even if only one gets used. These languages can interfere with each other, for example intruding into speech just when you do not expect them. And interference can manifest itself not just in vocabulary slip-ups, but even on the level of grammar or accent. “From research we know that whenever a bilingual or multilingual is speaking, both languages or all the languages that they know are activated,” says Mathieu Declerck, a senior research fellow at the Vrije Universiteit in Brussels. “For example, when you want to say ‘dog’ as a French-English bilingual, not just ‘dog’ is activated, but also its translation equivalent, so ‘chien’ is also activated.” As such, the speaker needs to have some sort of language control process. If you think about it, the ability of bilingual and multilingual speakers to separate the languages they have learned is remarkable. How they do this is commonly explained through the concept of inhibition — a suppression of the non-relevant languages. However, when this control system fails, intrusions and lapses can occur. For example, insufficient inhibition of a language can cause it to “pop up” and intrude when you are meant to be speaking in a different one.

Tamar Gollan, a professor of psychiatry at the University of California San Diego, has been studying language control in bilinguals for years. Her research has often led to counterintuitive findings. She explains that when mixing languages, multilinguals are navigating a sort of balancing act, inhibiting the stronger language to even things out — and sometimes, they go too far in the wrong direction. “When bilinguals are mixing languages, it seems like they inhibit the dominant language so much that they actually are slower to speak in certain contexts. I think the best analogy is: imagine you suddenly become better at writing in your non-dominant hand. We have been calling this reversed dominance.” Reversed dominance effects can be particularly evident when bilinguals switch between languages in a single conversation, says Gollan.

Navigating such interference could perhaps be part of what makes it hard for an adult to learn a new language, especially if they have grown up monolingual. One thing that might help is immersing yourself in the environment of the foreign language. “You are creating a context in which you are strongly holding back this other language, so that gives room for the other (new) language to become stronger,” says Matt Goldrick, a professor of linguistics at Northwestern University in Evanston, Illinois. “When you return from that immersion experience, hopefully you can better manage that competition,” he adds. “That competition will never go away, you just get better at managing it.”

Managing competition is certainly something that multilinguals do tend to have a lot of practice in. Many researchers argue that this brings them certain cognitive advantages — although it is worth noting that the jury’s still out on this, with others saying their own research does not show reliable evidence for a bilingual cognitive advantage. In any case, using languages is arguably one of the most complex activities humans learn how to do. And having to manage multiple languages has been linked to cognitive benefits in many studies, depending on task and age. Some studies have shown bilinguals perform better, for example, in activities when participants have to focus on counterintuitive information. Speaking multiple languages has also been linked to delayed onset of dementia symptoms. And of course, multilingualism brings many obvious benefits beyond the brain, not least the social benefit of being able to speak to many people.

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