User:Mr. Stradivarius/SLA theories summary

This is a draft of the "Second language acquisition theories" section in second language acquisition.

Process of acquisition
There has been much debate about exactly how language is learned, and many issues are still unresolved. There have been many theories of second language acquisition that have been proposed, but none has been accepted as an overarching theory by all SLA researchers. Due to the interdisciplinary nature of the field of second language acquisition, this is not expected to happen in the foreseeable future. However, there are various principles of second language acquisition that are agreed on by most researchers.

Input, output, and interaction
The primary factor affecting language acquisition appears to be the input that the learner receives. Stephen Krashen took a very strong position on the importance of input, asserting that comprehensible input is all that is necessary for second language acquisition. Krashen pointed to studies showing that the length of time a person stays in a foreign country is closely linked with their level of language acquisition. Further evidence for input comes from studies on reading: large amounts of free voluntary reading have a significant positive effect on learners' vocabulary, grammar, and writing. Input is also the mechanism by which people learn languages according to the universal grammar model.

While input is of vital importance, it does not appear to be the only factor involved in learning second languages. Krashen's assertion that only input matters in second language acquisition has since been rejected by most researchers. Output appears to play an important role, and among other things, can help provide learners with feedback, make them concentrate on the form of what they are saying, and help them to automatize their language knowledge. These processes have been codified in the theory of comprehensible output.

Researchers have also pointed to interaction in the second language as being important for acquisition. According to Long's interaction hypothesis the conditions for acquisition are especially good when interacting in the second language; specifically, conditions are good when a breakdown in communication occurs and learners must negotiate for meaning. The modifications to speech arising from interactions like this help make input more comprehensible, provide feedback to the learner, and push learners to modify their speech.

Form and meaning
The meaning of things being communicated is more important for second language acquisition than their form. There is a general agreement among researchers that learners must be engaged in decoding and encoding messages in the second language for the conditions to be right for second language learning. Learners must also be engaged in creating pragmatic meaning in order to develop fluency.

Some sort of focus on form does appear to be necessary for second language acquisition, however. Some advanced language structures may not be fully acquired without the opportunity for repeated practice. Schmidt's noticing hypothesis states that conscious attention to specific language forms is necessary for a learner's interlanguage to develop. This attention does not have to be in the form of conscious grammar rules, however; the attention is on how each specific form affects the meaning of what is being said.

Conscious and subconscious knowledge
Developing subconscious knowledge of the second language is more important than developing conscious knowledge. While conscious language knowledge is important for many aspects of second language acquisition, developing subconscious knowledge is vital for fluency. The knowledge that people use when they are speaking a language is mostly subconscious. It appears that learners can use conscious knowledge in speech if they have time and they are focused on form, but if these conditions are not met then they will fall back on subconscious knowledge. However, if learners have time to plan their speech, grammatical accuracy can improve.

It is not certain exactly how subconscious language knowledge is developed in the mind. According to skill-building theory, subconscious language knowledge is gained by practicing language until it becomes automatic. However, according to emergentist theories subconscious knowledge develops naturally from input and communication. The nature of the interface between conscious and subconscious language knowledge in the brain is also not clear; that is, it is not clear how conscious knowledge can develop into subconscious knowledge. It appears that conscious knowledge and subconscious knowledge are not completely separate, and practice at various aspects of language can lead to language knowledge becoming subconscious. However, studies have found that the two types of knowledge are stored differently in the brain, and this has led to the idea that conscious knowledge merely primes language acquisition processes rather than being directly involved. Both of these issues are still under debate.

Language processing
The way learners process sentences in their second language is also important for language acquisition. According to MacWhinney's competition model, learners can only concentrate on so many things at a time, and so they must filter out some aspects of language when they listen to a second language. Learning a language is seen as finding the right weighting for each of the different factors that learners can process.

Similarly, according to processability theory, the sequence of acquisition can be explained by learners getting better at processing sentences in the second language. As learners increase their mental capacity to process sentences, mental resources are freed up. Learners can use these newly freed-up resources to concentrate on more advanced features of the input they receive. One such feature is the movement of words. For example, in English, questions are formed by moving the auxiliary or question word to the start of the sentence (John is nice becomes Is John nice?) Beginner language learners cannot process this kind of movement; they must attend to the basic features of the input first.