Researchers in the Neuroscience of Language Lab at NYU Abu Dhabi are trying to figure out what happens in the bilingual brain when people switch between languages. For the first time, they have illustrated that switching languages when speaking and switching languages when listening engages different parts of the brain. They recently published their findings in The Journal of Neuroscience.
A key concept in the field of neuroscience is cognitive control — the idea that humans must be able to focus on certain tasks and block out unnecessary stimuli in order to accomplish a goal. A goal can be anything, from navigating one's way home from work, to ordering a coffee.
Knowing two languages — and switching between them — requires a great deal of cognitive control, since a language that is not in use at a particular time needs to be blocked off. This fact has led some scientists to believe that bilinguals have an advantage over monolinguals because knowing two languages requires more cognitive control than knowing one. Called the bilingual advantage hypothesis, this idea suggests that bilinguals' brains are in better shape to focus on given tasks and ignore unimportant stimuli. This gives bilinguals an advantage not only in the use of language, but also in any undertaking that requires focus.
Skeptics of the bilingual advantage hypothesis suggest that benefits would only come to bilinguals if the same control networks were used for both language tasks and non-language tasks.
"It's a big question in the field of language cognition, whether there is something special about language switching and language control that's particular to language, or whether the same brain machinery is applied for both language and non-language switching and control" said Esti Blanco-Elorrieta, a PhD candidate in psychology at NYU and lead author of the study.
Blanco-Elorrieta and her advisor, Associate Professor of Linguistics and Psychology at NYU Liina Pylkkänen, developed an experiment that tested switching languages and switching conceptual categories in both speaking and listening. The goal was to determine to what extent the regions of the brain engaged during these activities overlapped or were distinct.
Blanco-Elorrieta and Pylkkänen recruited 19 bilinguals who were fluent in Arabic and English. In the speaking phase of the experiment, participants were shown a playing card that could be numbered one to four, and were asked simply to say the number of the card. If the card was black, the participant was asked to respond in English; if the card was red, in Arabic.
In the listening phase, participants heard a number in either Arabic or English. They were then shown a playing card, and were asked to hit a button if the number they heard was the same as the number of the card. These two phases forced the participants to juggle both Arabic and English in their minds at the same time.
The next part of the experiment was designed to give the researchers information about what happens in a brain when the participants switched conceptual categories instead of switching languages. Participants were again shown cards and were asked to respond with the suit for a black card, or the number for a red card. They were also asked to confirm by pressing a button if a number or color they heard corresponded to the number or the color of the card they saw. This part of the experiment was all done in Arabic.
Blanco-Elorrieta and Pylkkänen used the magnetoencephalography (MEG) machine at the NYUAD Neuroscience of Language Lab to measure brain activity. The machine allowed the researchers to peer into the subjects' brains, and see what regions were activated at certain times. In this experiment, they focused on the period between 300 to 700 milliseconds after the participants were presented with the stimulus. This is the time when the participant's brain would be engaged to figure out the appropriate word to respond to the stimulus.
They found that in both production phases of the experiment, the prefrontal cortex was activated. Blanco-Elorrieta said that this is in line with previous research that has found the prefrontal cortex to be influential in cognitive control.
In the listening task where the subjects were exposed to two different languages, however, they found that the anterior cingulate cortex was engaged. "These findings show that different parts of the brain are used for switching between languages in speaking and listening, which is a novel finding because no one has done this kind of comparison before," Blanco-Elorrieta noted.
What's more, the researchers found that when listening, switching between languages (Arabic and English) and switching between categories (card number and card suit) enlisted different neural networks. This led them to argue that if the bilingual language hypothesis is indeed correct, benefits of being bilingual would apply only to productive tasks, and not to perceptive tasks.
Research like this is fundamental in the sense that it helps scientists learn how the brain processes language. But it could have a more practical application. "It could have pedagogical benefits," Blanco-Elorrieta said. "If, as it seems, producing and comprehending language switches relies on different brain mechanisms, we should make sure that both production and comprehension are sufficiently trained when teaching a second language, given that the cognitive control required to successfully deal with two languages seems to not straightforwardly extend from one type of language use to the other."
She added that Abu Dhabi is a fantastic place to do this kind of research, because there are so many people who speak a variety of languages. "We are always looking for volunteers," she said.