Over the past half century, scientists
have settled on two reasonable theories related to baby talk. One states that a
young child's brain needs time to master language, in the same way that it does
to master other abilities such as physical movement. The second theory states
that a child's vocabulary level is the key factor. According to this theory,
some key steps have to occur in a logical sequence before sentence formation
occurs. Children's mathematical knowledge develops in the same way.
In 2007, researchers at Harvard University, who were studying the two
theories, found a clever way to test them. More than 20,000 internationally
adopted children enter the US each year. Many of them no longer hear their birth
language after they arrive, and they must learn English more or less the same
way infants do—that is, by listening and by trial and error. International
adoptees don't take classes or use a dictionary when they are learning their new
tongue and most of them don't have a well developed first language. All of these
factors make them an ideal population in which to test these competing
hypotheses about how language is learned. Neuroscientists Jesse
Snedeker, Joy Geren and Carissa Shafto studied the language development of 27
children adopted from China between the ages of two and five years. These
children began learning English at an older age than US natives and had more
mature brains with which to tackle the task. Even so, just as with American born
infants, their first English sentences consisted of single words and were
largely bereft (缺乏的) of function words, word endings and verbs. The adoptees
then went through the same stages as typical American born children, though at a
faster clip. The adoptees and native children started combing words in sentences
when their vocabulary reached the same sizes, further suggesting that what
matter is not how old you are or how mature your brain is, but the number of
words you know. This finding—that having more mature brains did
not help the adoptees avoid the toddler-talk stage—suggests that babies speak in
baby talk not because they have baby brains, but because they have only just
started learning and need time to gain enough vocabulary to be able to expand
their conversations. Before long, the one-word stage will give way to the
two-word stage and so on. Learning how to chat like an adult is a gradual
process. But this potential answer also raises an even older
and more difficult question. Adult immigrants who learn a second language rarely
acheive the same proficiency in a foreign language as the average child raised
as a native speaker. Researchers have long suspected there is a "critical
period" for language development, after which it cannot proceed with full
success to fluency. Yet we still do not understand this critical period or know
why it ends.
单选题
What is the writer's main purpose in Paragraph 2?
A. To reject the view that adopted children need two languages.
B. To argue that culture affects the way children learn a language.
C. To give reasons why adopted children were used in the study.
D. To justify a particular approach to language learning.