Language acquisition

Language acquisition has been studied from the perspective of developmental psychology and neuroscience, which looks at learning to use and understand language parallel to a child's brain development. It has been determined through empirical research on developmentally normal children as well as through some extreme cases of language deprivation that there is a "sensitive period" of language acquisition in which human infants have the ability to learn any language. This plasticity is whittled down as a child becomes exposed to the specific sounds and structure of his or her language environment, and so the child quickly becomes a native speaker of that language. As Christophe Pallier noted, "Before the child begins to speak and to perceive, the uncommitted cortex is a blank slate on which nothing has been written. In the ensuing years much is written, and the writing is normally never erased. After the age of ten or twelve, the general functional connexions have been established and fixed for the speech cortex." According to the sensitive or critical period models, the age at which a child acquires the ability to use language is a predictor of how well he or she is ultimately able to use language.^[31] However, there may be an age at which becoming a fluent and natural user of a language is no longer possible. Our brains may be automatically wired to learn languages, but this ability does not last into adulthood in the same way that it exists during development. By the onset of puberty (around age 12), language acquisition has typically been solidified and it becomes more difficult to learn a language in the same way a native speaker would. At this point, it is usually a second language that a person is trying to acquire and not a first.^[32]
This critical period is usually never missed by cognitively normal children- humans are so well prepared to learn language that it becomes almost impossible not to. Researchers are unable to experimentally test the effects of the sensitive period of development on language acquisition because it would be unethical to deprive children of language until this period is over. However, case studies on abused, language deprived children show that they were extremely limited in their language skills even after instruction
Recent advances in functional neuroimaging technology have allowed for a better understanding of how language acquisition is manifested physically in the brain. Language acquisition almost always occurs in children during a period of rapid increase in brain volume. At this point in development, a child has much more neural connections than he or she will have as an adult, allowing for the child to be more able to learn new things than he or she would be as an adult.

Average Age	Language Development
6 months	Cooing, changes to distinct babbling by introduction of consonants
1 year	Beginning of language understanding; one-word utterances
12–18 months	Single word use; repertoire of 30-50 words (simple nouns, adjectives, and action words), which cannot as yet be joined in phrases but are used one at a time does not use functors (the, and, can, be) necessary for syntax, but makes good progress in understanding
18–24 months	Two-word (telegraphic) phrases ordered according to syntactic rules; vocabulary of 50 to several hundred words; understands propositional rules
2 years	New words every day; three or more words in many combinations; functors begin to appear; many grammatical errors and idiosyncratic expressions; good understanding of language
3 years	Full sentences; few errors; vocabulary of around 1,000 words
4 years	Close to adult speech competence