Bilingual speakers better able to focus on, find the right words
Monday, February 23, 2015
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Meredith Carlson Daly: About 22% of school-age children speak a language other than English at home, according to the US Census Bureau. The percentage is even higher, 64%, among Hispanic children. Still, it is commonly believed by some that teaching more than one language to children confuses them. Now, new research shows that in fact, bilingualism actually boosts the brain. Shifting back and forth between two different sets of vocabulary and grammar provide a real mental workout.
Consider for a minute the dual English-Spanish signs common in many parts of the United States, such as, "No Smoking," or "No Fumar"; "Danger" or "Peligro"; "Exit" or "Salida". Bilingual speakers must make these kinds of choices in big and small ways, all day, every day.
Our guest today is Viorica Marian, Professor of Communication Sciences and Disorders, Psychology and Cognitive Science at Northwestern University. Dr. Marian grew up in Romania, speaking multiple languages, and her research has found that bilingual speakers are better-equipped to focus and filter unnecessary information. This switching process boosts neural circuits, and in later life provides a hedge against Alzheimer's and other forms of dementia.
From the National Institutes of Health, I'm Meredith Carlson Daly (ph) and this is Research Developments, a podcast from the NIH's Eunice Kennedy Shriver National Institute of Child Health and Human Development, the NICHD, which partly funded Dr. Marian's work research.
Thank you for joining us -- today, Dr. Marian.
Viorica Marian: Thank you for having me. It's a pleasure to talk with you.
Ms. Daly: And can you tell us a little bit about what's going on in the brain that equips bilingual speakers to focus on what's in front of them, and filter out the extraneous information?
Dr. Marian: Sure. Well, everyone, regardless of whether monolingual or bilingual, is presented with a multitude of words every day. And as the world unfolds, the listener must map the sounds that they hear onto the correct word and its meaning. For bilinguals, this task is different because they know two languages, so the sounds that they hear need to be mapped onto the correct language, the language that is being spoken at that particular point in time, while ignoring any potentially conflicting mappings to the other language or languages that they know. So, because bilinguals have this constant experience with focusing on one language and ignoring another language, whether speaking with someone or listening to a teacher, or watching TV, they constantly have to select the correct language and inhibit the incorrect language, so they become increasingly good at attending to relevant information and inhibiting irrelevant information -- a skill known as inhibitory control.
So, in other words, because bilinguals are constantly juggling the two languages, they become really good mental jugglers. That's one way to think about it.
Ms. Daly: How did you conduct the study?
Dr. Marian: The study that we recently published, what we did is we had Spanish-English bilinguals and English monolinguals perform a word recognition task in English, and while they were doing this task we recorded their brain activity using functional magnetic resonance imaging. Many people are familiar with MRIs from getting scans of various body parts at their doctors' offices. So, functional MRIs are similar, except that they look at the brain and they record changes in blood flow in the brain areas associated with performing different tasks.
When the brain performs a task, the part of the brain where the task is being performed experiences changes in blood oxygenation levels. So, we recorded these changes in blood oxygenation levels and blood flow while listeners heard a word and had to select a picture corresponding to that word from a set of four images.
Now the tricky thing was that sometimes there were other pictures in that set with names that sounded similar, that started with similar sounds as the words that they had just heard. So for example, they may hear the word, "candy," and they see four images, and one of those images was a candle, so there was a candy, there were two other things, and there was a candle as well. Or, they may hear "clown," and see images not only of a clown but also a cloud.
Now, "candy" and "candle" sound a little similar, and "clown" and "cloud" also sound a little similar, but the task is to choose the correct picture, the one corresponding to the word that you just heard. So, we found that people were actually slower choosing the correct picture when there were competing words than when there were no competing words which makes sense, because as they hear the words they have to be able to successfully inhibit these competitors in order to perform the tasks correctly.
So, as I said, our study included Spanish-English bilinguals and English monolinguals, and we found that the English monolinguals showed more brain activation in the cortical areas that are known to be involved in executive control -- areas like the superior frontal gyrus, the anterior cingulate, suggesting that these areas had to work harder to accomplish the same goal that bilinguals were able to accomplish with less effort.
And this is because bilinguals have experienced mapping the sounds they hear onto words from different language, and making the correct selection while ignoring competition from the other language. So, they have a lot more experience with resolving competition between words and between languages.
Ms. Daly: And so that when you speak about the differences in brain functioning between monolingual speakers and bilingual speakers, I hear you saying that experience really does matter?
Dr. Marian: Yes, it does. So, our brains are malleable and just like with anything else, experience can change how our brains function, whether it's musical experience, whether it's a language experience, the experiences that we have continuously through our lives can influence neural cortical activation.
Ms. Daly: And the difference in inhibitory control that you spoke about, what might that mean for daily life and for later in life in terms of memory loss?
Dr. Marian: So, the task that we looked at was a linguistic task. As you hear words, how good are you at selecting the target word and inhibiting competing words. But, there is increasingly evidence in the literature that the inhibitory control advantages that bilinguals experience are not unique to language, and can be observed on other tasks that are not necessarily linguistic in nature. So for example, one well-known and well-studied task is a Stroop task. There are others as well as Simon task, but I'll just focus on the Stroop task to illustrate what I mean. In these inhibitory control tasks, what a person must do is focus on one important dimension and ignore other irrelevant dimensions while responding. In the Stroop task, you have to name the color of the ink in which a word is printed. So, if you see a word and it's printed in black ink, you say, "black." Or, you see it in red ink, you say, "red." Or, you see it in green ink, you say, "green." This task is very easy if the word that you see is not a color word.
It's also easy when the word that you see written up is the color that coincides with the ink color. So, if it says, "red," in red ink, then you say "red" without any difficulties. If you see the word, "black" in black ink, you again have no difficulty saying, "Black."
The tricky part is when you have to name the color of the ink, but the word that's written in that ink is a color that's different from the color of the ink. So, you may see the word, "blue," written in red ink, and you have to say "red" because you're just naming the color of the ink. You have to ignore the word that's written out.
And it's actually not as easy as it sounds. You can try it yourself, you can just write a list of words in different color ink, color words in different color ink, and try to name the color of the ink without processing the word itself. And there are also lots of videos online, you can go on YouTube and see lots of examples and just play along and test your own inhibitory control. You're much slower than when the word and the ink color coincide. Because you have to inhibit one input dimension, the word that you hear, and focus on another input dimension, the color of the ink.
And it's an easy task that people can do in a laboratory setting to very easily and relatively accurately measure inhibitory control, and what we find in our lab and in many other labs around the world is that oftentimes, bilinguals tend to be better and faster at performing this task -- that they are better able to inhibit the competing information and name the ink color correctly.
Ms. Daly: They have a kind of competitive advantage, because they have this experience of constantly having to choose?
Dr. Marian: They have constant experience with inhibiting the irrelevant language. It translates into inhibitory control advantage that's not specific to language, but could be in fact domain-general. That extends beyond language to other inhibitor control tasks as well, like in this case, a perceptual task. And it's not just a laboratory Stroop test, because inhibitory control, if we think of it, is really a hallmark of human cognition. People need to be able to inhibit conflicting information and focus on what matters all the time, no matter what task you're performing. Right now, you're listening to me speak. You have to be able to focus on my words and what I am saying, and ignore any distracting sounds in your environment or any distracting thoughts you may have. We are always needing to focus on something and ignore competing information.
So, it remains to be seen to what extent this advantage is that we see in linguistic inhibition and laboratory tasks like the Stroop task and the Simon task, extend beyond the laboratory to everyday environments. But there is already some preliminary evidence that it does in fact translate to some very interesting advantages -- advantages in memory, advantages in inhibitory control.
For example, we recently ran a study with school-age children, bilingual children, and monolingual children with collaborators in the United Kingdom, and found that the bilingual kids were better able to ignore background noise when listening to sentences and focus on the target sentences. But I think the most striking and the most exciting finding in the literature is a finding that comes from psychologist Ellen Bialystok's lab at York University, who found that bilingualism can postpone the onset of Alzheimer's Disease symptoms by as much as four to five years.
So, it is not that bilinguals will not develop Alzheimer's Disease, but if they do develop it, the onset is four to five years later than in monolingual. So, in other words, bilingualism improved inhibitory control and maybe offering this protective benefit against the cognitive decline associated with Alzheimer's.
Ms. Daly: Because it really does allow you to influence your neural structure?
Dr. Marian: It does. So, I have to say up front that it is important to understand that language is processed in a network of areas in the brain, so it's not as if we have one specific spot where one language is processed and another spot in the brain where the other language is processed. So, language, regardless of whether it's the first or the second language, gets processed in various areas depending on whether it is a comprehension task, or a production task -- whether competition is involved, and so on. And just like anything else, there's this "use it or lose it" statement that we know, with the brain and with using the language or with practicing a skill. People often engage in solving word puzzles or Sudoku puzzles to give their brain a workout. And bilingualism does something similar to the brain in that it offers you this constant workout, you're constantly focusing on one language and inhibiting another language. So, without having to go out of your way, you are constantly exercising your brain, which is what drives some of these cognitive advantages we're seeing.
Now, in many ways we are now only beginning to scratch the surface of understanding how the brain works, and neuroscience as a field is a much younger science than, say, physics and chemistry. We are now only in the very early stages of understanding how the bilingual brain is different from or similar to the monolingual brain, but it's a very exciting area that has a lot of potential, and a lot of promise, I think.
Ms. Daly: Tell us what's next for your research.
Dr. Marian: Next we want to look at what happens when the word you hear is in one language, but the competition is from the other language. So for example, you may hear the word, "marker," but see not only a marker, but also "mariposa," which is the Spanish word for butterfly. Or the other way around, you may hear "mariposa," and you see a marker in addition to the butterfly. So, we would like to record the brain activity of Spanish-English bilinguals as they perform these tasks, to see how competition between different languages is similar or different from competition in the same language at a cortical level.
And this is part of our broader research program of understanding the consequences of bilingualism. We want to understand how knowing more than one language can change human function. How does it change language learning? How does it change learning in general? How does it change perception? Not only auditory perception, but also visual perception, since the two modalities are highly-interactive. How does it change memory and cognitive function? Broad questions like, what are the implications for brain health, for mental health, for decision making in general. This is just some of the questions we are interested in.
And as you mentioned yourself earlier in the podcast, the majority of the world population is bilingual or multilingual. It is very common for people all around the world to grow up speaking more than one language or to learn additional languages later in life, or both -- grow up with a couple of languages, and add on languages as they grow up. And yet the way -- for the longest time, scientists who studied cognition or the brain or language focused primarily on monolinguals, rendering the findings incomplete or maybe even inaccurate at describing the full human linguistic function, because it was leaving a large segment of the population unrepresented or under-represented in research.
Of course, there are various tasks some bilinguals perform better than monolinguals, and others they perform similar, and another they may perform worse -- but overall, bilingual is not disadvantageous and doesn't have negative consequences. And the -- if you think about bilinguals doing worse than monolinguals, it's not that bilingualism is bad for you. It's that a lot of those bilinguals come from poorer backgrounds, lower social-economic classes, especially in the United States. So, in that case, it's poverty and not bilingualism that's really bad for you. Bilingual, as it turns out, is a good thing -- and if you look at places like Europe or Canada, the bilingual Canada, there are no negative effects on cognition from bilingualism. So, it's important to understand that.
Ms. Daly: Well, thank you for clarifying your research. I've been speaking with Dr. Viorica Marian, lead author of the study, "Differential Recruitment of Executive Control Regions During Phonological Competition in Monolinguals and Bilinguals," which was recently published in the journal, "Brain and Language." Dr. Marian, thank you so much for joining us today.
Dr. Marian: Thank you, it was my pleasure.
About the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD): The NICHD sponsors research on development, before and after birth; maternal, child, and family health; reproductive biology and population issues; and medical rehabilitation. For more information, visit the Institute's website at http://www.nichd.nih.gov/.