page_title: Language acquisition
section_title: Sensitive period
hierarchical_section_title: Language acquisition / Representation in the brain / Sensitive period
caption_attribution_description: English: This chart shows the different stages of language acquisition
context_page_description: Language acquisition is the process by which humans acquire the capacity to perceive and comprehend language, as well as to produce and use words and sentences to communicate.
  Language acquisition involves structures, rules and representation. The capacity to successfully use language requires one to acquire a range of tools including phonology, morphology, syntax, semantics, and an extensive vocabulary. Language can be vocalized as in speech, or manual as in sign. Human language capacity is represented in the brain. Even though human language capacity is finite, one can say and understand an infinite number of sentences, which is based on a syntactic principle called recursion. Evidence suggests that every individual has three recursive mechanisms that allow sentences to go indeterminately. These three mechanisms are: relativization, complementation and coordination.
  There are two main guiding principles in first-language acquisition: speech perception always precedes speech production, and the gradually evolving system by which a child learns a language is built up one step at a time, beginning with the distinction between individual phonemes.
context_section_description: 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. Several researchers have found that from birth until the age of six months, infants can discriminate the phonetic contrasts of all languages. Researchers believe that this gives infants the ability to acquire the language spoken around them.  After this age, the child is able to perceive only the phonemes specific to the language being learned. The reduced phonemic sensitivity enables children to build phonemic categories and recognize stress patterns and sound combinations specific to the language they are acquiring. As Wilder Penfield 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 connections 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. However, there may be an age at which becoming a fluent and natural user of a language is no longer possible; Penfield and Roberts (1959) cap their sensitive period at nine years old. The human brain may be automatically wired to learn languages, but this ability does not last into adulthood in the same way that it exists during childhood. By 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. Just like children who speak, deaf children go through a critical period for learning language. Deaf children who acquire their first language later in life show lower performance in complex aspects of grammar. At that point, it is usually a second language that a person is trying to acquire and not a first.
  Assuming that children are exposed to language during the critical period, acquiring language is almost 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 exhibit extreme limitations in language skills, even after instruction.
  At a very young age, children can distinguish different sounds but cannot yet produce them.  During infancy, children begin to babble. Deaf babies babble in the same patterns as hearing babies do, showing that babbling is not a result of babies simply imitating certain sounds, but is actually a natural part of the process of language development.  Deaf babies do, however, often babble less than hearing babies, and they begin to babble later on in infancy-- at approximately 11 months as compared to approximately 6 months for hearing babies.
  Prelinguistic language abilities that are crucial for language acquisition have been seen even earlier than infancy. There have been many different studies examining different modes of language acquisition prior to birth. The study of language acquisition in fetuses began in the late 1980s when several researchers independently discovered that very young infants could discriminate their native language from other languages. In Mehler et al. (1988), infants underwent discrimination tests, and it was shown that infants as young as 4 days old could discriminate utterances in their native language 
caption: The phases of language acquisition in children
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