Early Childhood Critical Time to Learn Sign Language
Those who start young use brain region others can't
TUESDAY, Jan. 8, 2002 (HealthDayNews) -- People who learn sign language from birth use a brain region that those who learn to sign later in life can't access, a new study suggests.
The visual and spatial demands of sign language appear to activate a specific part of the brain, the researchers say. However, only those who learn non-spoken languages from birth seem to develop the full potential of this brain area.
The findings could help explain why as with spoken languages those who learn sign languages later in life never become fluent, and they could also have implications for how non-spoken languages are taught. The study appears in the January issue of the journal Nature Neuroscience.
Researchers have known for years that a part of the brain's left hemisphere, called the left angular gyrus, is involved in spoken languages. This latest study suggests that a matching part of the right side of the brain may be crucial for fluency in such non-spoken languages as American Sign Language (ASL).
Aaron J. Newman, a graduate research fellow in psychology at the University of Oregon, led the study, which involved 27 people. All the volunteers could hear, but 16 had learned ASL from birth because they had deaf parents, while the other 11 had learned ASL in early adulthood.
The volunteers watched a screen while a functional magnetic imaging (fMRI) scan revealed activity in different areas of their brains. While inside the scanner, they were asked to read written English sentences or meaningless jumbles of consonants that were projected on the screen. Then, they were told to read both ASL sentences and gestures that looked similar to ASL signs but meant nothing.
"In the left hemisphere, we found the same classical language areas were activated in all the subjects," Newman says. "In the right hemisphere, there was one area in the temporal lobes that was activated in all the subjects, regardless of when they learned sign language."
However, during the ASL portion of the test, Newman says, a region of the brain's right hemisphere called the right angular gyrus lit up in the volunteers who had learned ASL from birth. The volunteers who learned ASL after puberty showed far less activity in that part of their brain.
Previous studies have suggested the right hemisphere is more important for performing visual and spatial tasks.
"It makes sense that when you're using a language that relies on space, you use these same brain areas," Newman says.
Rachel I. Mayberry, director of communication sciences and disorders at McGill University in Montreal, Quebec, says the brain treats a lot of sign language in the same way as spoken language, using the left hemisphere.
However, the discovery of activation of in the right angular gyrus in people who learned ASL from birth suggests fluency in the language requires that region's specialized skills.
"Sign language is very spatial. Its grammar is very spatial," Mayberry says. "Whether your hand is going to the left or the right can make the difference between the subject or the object."
Newman says the findings suggest there is a critical period for learning both spoken and sign languages.
He suspects the right angular gyrus, like other brain structures, is more "plastic," or adaptable, during childhood. At that stage, it can be recruited for language tasks, whereas later in life it can't become specialized for language.
"Early language exposure is really important," Newman says. "When we see differences in proficiency related to language acquisition and age of language acquisition, it probably is due to differences in brain plasticity."
The researchers don't yet know whether the right angular gyrus is involved in understanding the grammar, the meaning or the forms of the words, or why this particular brain region is so crucial to sign language. They plan to study that in future research.
What to Do: Find out more about American Sign Language from the Animated American Sign Language Dictionary, the National Institute on Deafness and Other Communication Disorders or the National Association of the Deaf.