Individual variation in second-language acquisition is the study of why some people learn a second language better than others. Unlike children who acquire a language, adults learning a second language rarely reach the same level of competence as native speakers of that language. Some may stop studying a language before they have fully internalized it, and others may stop improving despite living in a foreign country for many years. It also appears that children are more likely than adults to reach native-like competence in a second language. There have been many studies that have attempted to explain these phenomena. A flurry of studies in the 1970s, often labelled the "good language learner studies", sought to identify the distinctive factors characteristic of successful learners. Although those studies are now widely regarded as simplistic, they did serve to identify a number of factors affecting language acquisition. More detailed research on many of these specific factors continues today. For this reason, individual variation in second-language acquisition is not generally considered a single area of research. Rather, it is simply a convenient way to categorize studies about language aptitude, age and language learning, strategy use, and affective factors that affect language acquisition.
Language aptitude
There are two definitions that help explain individual difference variables. The first is predictive. Language aptitude is related to a set of cognitive abilities. These cognitive abilities allow one to predict how well an individual can learn a foreign language. These abilities change under limited time and circumstances. The second definition is interactional. It views language aptitude as comprehension abilities during second language learning. Aptitude is or can be subject to change according to an environment. It highlights that no specific instruction works for all second language learners. Therefore, in order for an individual to grasp a second language, there must be an adaption. Where the learner’s abilities can flourish under different learning conditions. A meta-analysis brought to light that the importance of aptitude is an overestimate when it comes to grammatical capability. In specific conditions, language aptitude is a conscious construct which affects learning results. Language aptitude can be useful in predicting the beginning stages of second language learning, when it comes to grammatical competence, but it is not a reliable way to learning stages. Tests of language aptitude have proven extremely effective in predicting which learners will be successful in learning. However, considerable controversy remains about whether language aptitude is properly regarded as a unitary concept, an organic property of the brain, or as a complex of factors including motivation and short-term memory. Research has generally shown that language aptitude is quite distinct from general aptitude or intelligence, as measured by various tests, and is itself fairly consistently measurable by different tests. Language aptitude research is often criticized for being irrelevant to the problems of language learners, who must attempt to learn a language regardless of whether they are gifted for the task or not. This claim is reinforced by research findings that aptitude is largely unchangeable. In addition, traditional language aptitude measures such as the Modern Language Aptitude Test strongly favor decontextualized knowledge of the sort used in taking tests, rather than the sort used in conversation. For this reason little research is carried out on aptitude today. However, operators of selective language programs such as the United States Defense Language Institute continue to use language aptitude testing as part of applicant screening.
Age
How children acquire native language (L1) and the relevance of this to foreign language (L2) learning has long been debated. Although evidence for L2 learning ability declining with age is controversial, a common notion is that children learn L2s easily and older learners rarely achieve fluency. This assumption stems from ‘critical period’ (CP) ideas. A CP was popularised by Eric Lenneberg in 1967 for L1 acquisition, but considerable interest now surrounds age effects on second-language acquisition (SLA). SLA theories explain learning processes and suggest causal factors for a possible CP for SLA, mainly attempting to explain apparent differences in language aptitudes of children and adults by distinct learning routes, and clarifying them through psychological mechanisms. Research explores these ideas and hypotheses, but results are varied: some demonstrate pre-pubescent children acquire language easily, and some that older learners have the advantage, and yet others focus on existence of a CP for SLA. Recent studies have recognised that certain aspects of SLA may be affected by age, though others remain intact. In terms of specific ages, Steven Pinker and colleagues conducted a large-scale internet study aimed at measuring individual’s age, English proficiency, and amount of time spent practicing English. The findings suggest that the ability to learn a new language with fluency declines after age 18 and must begin by age 10. There are three main factors why our ability to acquire a new language declines after the age of 18. First, significant social changes usually occur at the age of 18. For example, during this period of time individuals may be heading off to college or entering the workforce. As a result, less time is dedicated towards learning a new language. Secondly, an individual’s primary language may impede the development of a newer language. The grammatical rules of our first language become more readily available in our minds as we are exposed to our first language in larger quantities. Lastly, our brains are still developing. In this case, learning becomes more difficult because the brain is undergoing significant changes during our late teenage years and early-20s.
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