SPEAK early, or forever hold your peace. At last week鈥檚 meeting, researchers
revealed that children deprived of language in their first five years never
become fluent.
Scientists think there is a critical window for mastering a second language:
if you don鈥檛 nail it down before your early teens, you鈥檒l never sound like a
native. But no one was sure if you had to learn your first language by a certain
age.
That鈥檚 because first language acquisition is hard to study. Almost all
children are exposed to language from the minute they鈥檙e born, and if they don鈥檛
pick it up in their first few years, abnormalities in the brain鈥檚 language
centres are usually to blame. But Rachel Mayberry at McGill University in
Montreal came up with a way of answering the question鈥攂y studying healthy
children who were deaf but had learned sign language at various ages up to
13.
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The team studied 30 adult volunteers who used sign language as their main way
of communicating. A third of them learned sign language as toddlers, another
third started to learn it at school aged between 4 and 7, and the remainder
didn鈥檛 learn it until they were between 8 and 13.
Mayberry asked the volunteers to judge whether signed sentences were
grammatically correct. Children of signing parents did very well. Those who
learned to sign when they went to primary school were not nearly so proficient,
and late learners performed barely better than chance.
Mayberry was also interested in how first language acquisition affects how
easily a child learns a second. So she recruited 39 adult volunteers who learned
English as a second language between the ages of 5 and 8. Hearing volunteers
spoke Urdu as their first language. A group of deaf volunteers had used sign
language from early childhood. A third group learned sign after age 5, and had
no fluent language before that.
When the subjects were tested on English comprehension, Mayberry found a gulf
in abilities. Both Urdu-speaking and early signing volunteers understood
sentences as well as native speakers, but late learners had problems
understanding all but the simplest sentences. 鈥淭heir scores were comparable to
people who鈥檝e had strokes,鈥� she says.
鈥淔ailure to learn a language early in life impairs your ability to learn
language throughout life,鈥� Mayberry concludes. She thinks that if brain circuits
for language aren鈥檛 stimulated, they are lost.
Mary Pat Moeller of the Boys Town National Research Hospital in Omaha,
Nebraska, stressed that early intervention can save a deaf child from this fate.
Her research shows that children who are taught sign language from 11 months of
age usually have vocabularies and IQs comparable to their hearing peers by age 5.