Second language acquisition

Second-language acquisition (SLA), second-language learning, or L2 (language 2) acquisition, is the process by which people learn a second language. Second-language acquisition is also the scientific discipline devoted to studying that process. The field of second-language acquisition is a subdiscipline of applied linguistics, but also receives research attention from a variety of other disciplines, such as psychology and education.

A central theme in SLA research is that of interlanguage, the idea that the language that learners use is not simply the result of differences between the languages that they already know and the language that they are learning, but that it is a complete language system in its own right, with its own systematic rules. This interlanguage gradually develops as learners are exposed to the targeted language. The order in which learners acquire features of their new language stays remarkably constant, even for learners with different native languages, and regardless of whether they have had language instruction. However, languages that learners already know can have a significant influence on the process of learning a new one. This influence is known as language transfer.

The primary factor driving SLA appears to be the language input that learners receive. Learners become more advanced the longer they are immersed in the language they are learning, and the more time they spend doing free voluntary reading. The input hypothesis developed by linguist Stephen Krashen makes a distinction between language acquisition and language learning (acquisition–learning distinction), claiming that acquisition is a subconscious process, whereas learning is a conscious one. According to this hypothesis, the acquisition process in L2 is the same as L1 (Language 1) acquisition. The learning process is consciously learning and inputting the language being learned. However, this goes as far as to state that input is all that is required for acquisition. Subsequent work, such as the interaction hypothesis and the comprehensible output hypothesis, has suggested that opportunities for output and for interaction may also be necessary for learners to reach more advanced levels.

Research on how exactly learners acquire a new language spans a number of different areas. Focus is directed toward providing proof of whether basic linguistic skills are innate (nature), acquired (nurture), or a combination of the two attributes. Cognitive approaches to SLA research deal with the processes in the brain that underpin language acquisition, for example how paying attention to language affects the ability to learn it, or how language acquisition is related to short-term and long-term memory. Sociocultural approaches reject the notion that SLA is a purely psychological phenomenon, and attempt to explain it in a social context. Some key social factors that influence SLA are the level of immersion, connection to the L2 community, and gender. Linguistic approaches consider language separately from other kinds of knowledge, and attempt to use findings from the wider study of linguistics to explain SLA. There is also a considerable body of research about how SLA can be affected by individual factors such as age, learning strategies, and affective factors. A commonly discussed topic regarding age in SLA is the critical period hypothesis, which suggests that individuals lose the ability to fully learn a language after a particular age in childhood. Another topic of interest in SLA is the differences between adult and child learners. Learning strategies are commonly categorized as learning or communicative strategies, and are developed to improve their respective acquisition skills. Affective factors are emotional factors that influence an individual's ability to learn a new language. Common affective factors that influence acquisition are anxiety, personality, social attitudes, and motivation.

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