By the 1980s, the theories of Stephen Krashen had become the prominent paradigm in SLA. In his theories, often collectively known as the Input Hypothesis, Krashen suggested that language acquisition is driven solely by comprehensible input, language input that learners can understand. Krashen’s model was influential in the field of SLA and also had a large influence on language teaching, but it left some important processes in SLA unexplained. Research in the 1980s was characterized by the attempt to fill in these gaps. Some approaches included Lydia White’s descriptions of learner competence, and Manfred Pienemann’s use of speech processing models and lexical functional grammar to explain learner output. This period also saw the beginning of approaches based in other disciplines, such as the psychological approach of connectionism.
The 1990s saw a host of new theories introduced to the field, such as Michael Long’s interaction hypothesis, Merrill Swain’s output hypothesis, and Richard Schmidt’s noticing hypothesis. However, the two main areas of research interest were linguistic theories of SLA based upon Noam Chomsky’s universal grammar, and psychological approaches such as skill acquisition theory and connectionism. The latter category also saw the new theories of processability and input processing in this time period. The 1990s also saw the introduction of sociocultural theory, an approach to explain second-language acquisition in terms of the social environment of the learner.
There is no agreement on a “complete” theory of second language acquisition yet.
Each theoretical framework has a different focus and its limitations.
Behaviorism: emphasizing stimuli and responses, but ignoring the mental processes that are involved in learning.
InnateLAD, based on intuitions
Information processing and connection-ism: involving controlled laboratory experiments where human learning is similar to computer processing.
Interactionistposition: modification of interaction promotes language acquisition and development.