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Researchers Work To Better Understand Brains Of Deaf Language Learners

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The GUMC study is the first of its kind, since it separates deaf people whose native language is English, from those whose native language is American Sign Language (ASL).
Courtesy of Georgetown University Medical Center
The GUMC study is the first of its kind, since it separates deaf people whose native language is English, from those whose native language is American Sign Language (ASL).

What we experience and learn helps shape our brains, but a group of researchers at Georgetown University Medical Center have shown that the language we first learn can affect our brain structure in fascinating ways.

Now, this new study isn’t about a person who first learns English versus a person whose native language is French or Russian. No, this study is about a person like Daniel Koo, an associate professor at Gallaudet University in the psychology department.

First language matters

Koo was born deaf. But American Sign Language was not the first language he learned.

“I grew up originally in the oral methodology, meaning learning English through lip reading. And later I learned sign language as a second language,” he explains.

And that experience, he says, is actually pretty common.

“90 percent of deaf children are born to parents who can hear, so many deaf children use English as a first language, just like I did growing up,” he says.

Gallaudet associate professor Daniel Koo assisted with the GUMC study; he was born deaf, and learned English before ASL. (Gallaudet University)

The thing is, though: most studies on deafness have been conducted only with people who use ASL as a first language.

“They never looked at the cross-section of deaf people who are also primarily English users,” says Koo. “But we can't assume too many things just from one specific population who grew up in one specific language experience. So we were the first study to really look at both groups of deaf people and compare the structures that are impacted by those language choices that are made developmentally as they are growing up.”

And that was a huge revelation for GUMC post-doctoral fellow Olumide Olulade, the study’s lead author.

“I always thought that everyone who was deaf used sign language,” he says. “And to find out that most of the people who are deaf actually grow up using English, I think it’s important that our scientific studies, from a scientific perspective, provide information that can be used for the full population.”

To that end, he explains, the research team used magnetic resonance imaging, or MRI, to analyze the brains of four different groups: deaf people who grew up using American Sign Language, deaf people who grew up using English, hearing people who grew up using American Sign Language (which they learned from their deaf parents) and hearing people who grew up using English.

And what the team found was that with all deaf participants — regardless of their native language — their auditory cortex looked different from their hearing counterparts. Mainly, it had a smaller volume of white matter – that’s the tissue affecting how the brain learns and functions.

“But what we found is that if you are raised using American Sign Language, you also find some of those differences in parts of the brain that help us speak or use language,” says Guinevere Eden, who directs GUMC’s Center for the Study of Learning.

How learning happens

What she’s speaking of is gray matter, which serves to process information. The study found the volume of right-hemisphere gray matter of deaf native ASL users is thicker than that of deaf native English users.

Why? Perhaps because the right hemisphere handles visual-spatial skills. And with its unique system of grammar — along with its movement of the hands, face and torso — ASL is more spatial. English is more linear.

“Now it doesn't mean that one or the other is better,” Eden says. “But I think the interesting question will be, when we study things in education, whether it’s how we teach reading or how we do interventions, it’s interesting to have that background information: knowing that it’s not just your sensory experience that shapes the brain, but your language experience, and that they interact with one another.”

That’s the biology of learning. And once we understand how learning happens, we can adjust our teaching methods so they'll have the greatest effect. But whatever the method, says Daniel Koo, when it comes to teaching language to a child who’s deaf or hard of hearing: “It’s important that the deaf child just gets access, and has complete access to a language, as early as possible, regardless of English or sign language. It’s important that they get that exposure,” he explains.

Because that exposure will help them connect with their world, engage with their community, and, perhaps, one day teach their children, too.

Music: "Language of Love" by Skyline Motel from Skyline Motel


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