Definition
Second language acquisition (SLA) is the process of learning one or more additional languages as opposed to acquring one’s first language.
Children and adults typically learn a second language either after the critical period or in a setting where they are not directly exposed to the target language.
Brief History
SLA just like its FLA counterpart was the subject of much research and inquiry throughought history. Diplomats, traders and individuals have been learning foreign languages since the beginning of early civilizations when different linguistic groups needed to interact with each other. This field of learning eventually saw sigificant advances with the industrial revolution and the emergence of new learning theories, models, and methods grounded in scientific research.
Modern Understanding
SLA generally builds upon existing research in the fields of learning psychology, First Language Acquisition (FLA), and neuroscience. There is ample evidence today suggesting children who are unable to acquire a language during the critical period due to a variety of reasons (see first language acquisition), will never be able to learn to fluently use any language -first or second- later in life. Likewise delaying acquisition of a first language may affect both first and second language fluency later in life.
One important finding of SLA research, is the concept of interlanguage which suggests that second language learning is initially built upon a learner’s first language and eventually grows to become its own independant language over time distinct from both the learner’s first language and target language. As learners make progress in the second language their interlanguage grows to become closer to the target language as would be spoken by a native speaker. In a majority of cases SLLs’ interlanguage never equates that of native speakers of the target language.
Several domains of research have advanced the field in recent years with cognitive science, social sciences, and psychology informing the design of new methods of language learning designed to make second language learning more effective and efficient. Evidence shows that language learning is affected by cognitive, neurological, emotional, socio-cultural, psychological, and biological factors.
Classroom based SLA vs Immersion based SLA
The scope of SLA research ususally falls under multiple domains with classroom based SLA and immersion SLA seeing much interest. Some researchers have opted to make a dinstinction between active learning in the case of classroom or self-motivated study of the language as opposed to natural aquisition of a second language in an immmersive setting. Most likely, learners will be exposed to both suvtypes of SLA at different stages of their learning journey.
Language fossilization and attrition
Second language learners may reach a plateau called fossilization where learning progress halts or slows down considerably. This period of decreased learning progress may happen for a variety of reasons irrespective of whether the learner is still actively using the L2. Likewise, learners who stop using their L2 run the risk of L2 attrition where they start forgetting their L2 and losing fluency. This phenomenon was observed in both SLL as well children who were not able to learn a first language at all during their critical period. Language attrition also appears to affect learners’ first language in cases where learners are immersed in their L2 while becoming isolated from their L1. In such cases attrition was found to be most often limited to vocabulary but not pronunciation or grammar unless affected by socio-cultural factors or language transfer from the L2 and as long as the switch had occurred post critical period.