Age Effects in Second Language Acquisition : Overview
Rieko Matsuoka, Ian Smith
Abstract Age has been regarded as an important factor in acquiring second languages successfully as well as in acquiring first languages. In this review article, previous studies regarding age and language acquisition are examined, and the ways in which age may affect the process of acquiring a second language are discussed. For instance, some previous research（ e.g., Johnson & Newport, 1989） evidenced the strong negative correlation（r > |－.7|） between age of acquisition/arrival and accuracy or native-like proficiency, which means the younger learners are, the more native-like they become. This correlation supports the critical period hypothesis. The focus of this study is on examining whether the critical period hypothesis
in first language acquisition is valid in second language acquisition. Some studies have revealed that adult learners whose age of acquisition/arrival is after puberty are not successful in acquiring a native-like proficiency in a second language, which again supports the critical period hypothesis; whilst others have shown cases where adult learners reached a native-like proficiency, thus refuting the critical period hypothesis. Finally, some pedagogical implications are drawn, using previous interdisciplinary studies in areas such as neuropsychology and phonology. These implications may help adult learners wanting to enhance their proficiency in a second language.
Second language acquisition researchers differ over when the critical period/sensitive period comes to an end. In first language acquisition research, as Lenneberg（ 1967） posits, the critical period ends at puberty, and humans are believed to fail to acquire a first language in cases where they are unable to expose
themselves to a human language before puberty, which is illustrated by Genie’s case in some pieces of literature（ e.g. Brown, 1968; Jones, 1995）. In second language acquisition, some researchers（ e.g. Birdsong, 2006, Birdsong & Park, In Press） claim the cutting-off age should be at puberty or at 12 years of age, the same as in first language acquisition. However, others postulate a younger age such as six years old（ e.g. Long, 1990） or an older one such as 18 years old（ e.g. Bialystok &
Hakuta, 1994） as the terminal point of the critical period/sensitive period, depending on the focal area of acquisition, i.e., whether in phonology/pronunciation（ in the younger case） or mophosyntax/grammar（ in the older case).
Different in character from first language acquisition, which humans undergo unconsciously, second language acquisition becomes more difficult and is rarely entirely successful after a certain period, i.e., the critical period/sensitive period. Selinker （1972） named this phenomenon fossilization. Many second language learners fail to reach target-language competence and establish their own internalized rule system, which is called interlanguage（ Selinker, 1972）. Ellis（ 1994） suggests that age is one of the internal factors of fossilization, arguing that
learners reach a critical age when their brains lose plasticity and certain linguistic features cannot be mastered.
Ellis（ 1994, p. 494） consolidated his research into age and second language acquisition and made proposals in six areas – in （a） sensory acuity,（ b） neurological factors,（ c） affectivemotivational factors,（ d） cognitive factors,（ e） input, and（ f） storage. In terms of sensory acuity, children or younger learners
are better in their ability to perceive and segment sounds in a second language. This leads to more native-like pronunciation among younger learners. Neurologically, loss of plasticity or lateralization and cerebral maturation, which occur at certain
ages, have been proved to affect learners’ abilities to acquire both pronunciation and grammar. Certain ages are the cuttingoff points for the so-called ‘critical period’ or ‘sensitive period’. Therefore, neurological structure may affect both pronunciation and grammar. Regarding affective and motivational factors, child learners are, in general, more strongly motivated to communicate with native speakers and to integrate culturally because they are less conscious and suffer less from anxiety about communicating in a second language. In cognitive areas, points for the so-called ‘critical period’ or ‘sensitive period’. Therefore, neurological structure may affect both pronunciation and grammar. Regarding affective and motivational factors, child learners are, in general, more strongly motivated to
communicate with native speakers and to integrate culturally because they are less conscious and suffer less from anxiety about communicating in a second language. In cognitive areas, children use their language acquisition device, while adult
learners rely on inductive learning abilities in learning a second language. In the process of inputting the language information, children input it more efficiently than adults, who may utilize more negotiation of meaning. Lastly the difference exists in the means of storage. Young children store first language and second language information separately and become coordinate bilinguals whilst adult learners store first language and second language knowledge together and become compound bilinguals. Coordinate bilinguals can use both languages automatically
whilst compound bilinguals cannot.
Brain-based evidence has been also coordinated with second language research in recent studies（ e.g. Birdsong, 2006 for review; Ullman, 2001, 2007）, looking at whether the process of second language acquisition is conducted in the same
way as, a similar way to or a different way from the process of first language acquisition.
Selinger（ 1978） proposes, there may be multiple critical/sensitive periods for different aspects of language.
Oyama（1976） examined 60 male learners who had immigrated to the United States. Their ages ranged from 6 to 20 years old and they had lived there for between 5 and 18 years. Two adult native speakers judged the ‘native-ness’ of the learners’ accents during a reading-aloud task and during free speech. The results showed a
significant negative correlation in ‘age of arrival and acquisition’, which meant that the younger their age of arrival was, the more authentic the accent they acquired. For instance, the youngest arrivals were rated the same as native speakers. However, no significant relationship was found between the length of stay and their accent.
Similar results have been provided from studies in morphosyntax/grammar, but in their studies the cutting-off age for the critical/sensitive period is later or older than the studies on pronunciation. Patkowski （1980） investigated 67 immigrants to the United States, finding that learners who had entered the United States before the age of 15 were rated as more proficient in grammar than learners who had entered after the age of 15.
The range of adult group scores was smaller than the range of child group scores. In addition, Patkowski examined the effects of the length of the stay in the United States, the amount of informal exposure to English and the amount of formal instruction. Neither the length of the stay nor the amount of formal instruction provided a significant effect but the amount of informal exposure did have a significant effect, though this was much less significant than the age factor.
In a similar line to Patkowski（ 1980）, Johnson & Newport （1989） investigated 46 native Koreans and Chinese who had immigrated in the United States between the ages of 3 and 39, using an aural grammaticality judgment test. Half of them arrived there before the age of 15 and the other half arrived after the age of 17. The participants were asked to judge the grammaticality of 276 spoken sentences. The results indicated a negative correlation between age at arrival and judgment scores, which was – 0.77, meaning that the later the learner arrived, the lower the score they got. However, one difference from Patkowski’s study was that the scores of the younger group varied less than those of the adult group. Also, neither the number of years of exposure to English nor the amount of classroom instruction was related to the grammaticality judgment scores. Johnson（ 1992） followed up on the study by Johnson & Newport（ 1989） by using the same participants in the earlier study a year later with written tests, working on the belief that written test materials eliminated extragrammatical properties that were present in the auditory materials. The results showed a negative correlation（ r = – 0.54） between age of arrival and performance, and suggested that the grammatical knowledge of young learners is native or near-native whereas that attained by older learners is ill-formed or incomplete. Thus, the critical period effects could be found in a test of grammar with a minimum number of extragrammatical properties.
DeKeyser （2000） tested the fundamental differencebhypothesis （Bley-Vroman, 1988）, which states that while children are known to learn a language almost completely through implicit domain-specific mechanisms, adults have largely lost the ability to learn a language without reflecting on its structure and they have to use alternative mechanisms, drawing especially on their problem-solving capacities, to learn a second language. The hypothesis implies that only adults with a high level of ‘verbal analytical’ ability will reach near-native competence in their second language, but that this ability is not a significant predictor of success in childhood second language acquisition. A study of 57 adult Hungarian-speaking immigrants confirmed the hypothesis. Very few adult immigrants scored in the range achieved by child arrivals in a grammaticality judgment test.
Harley （1986） investigated the levels of attainment of children in French bilingual programs in Canada, focusing on the learners’ acquisition of French verb rules. She compared early and late immersion students after both had received 1,000 hours of instruction, using data from interviews, a story repetition task and a translation task. The older students demonstrated better overall control. However, at the end of their schooling, the early immersion group showed higher levels of ability than the older group.
The morpheme studies（ Bailey, Madden & Krashen, 1974; Fathman, 1975） showed that the order of acquisition of English morphemes was the same for children and adults. They showed that adults go through the same stages of acquisition of morphemes as children and therefore age does not appear to be a factor here.
Cummins（ 1981） formulated the ‘interdependency principle’ to refer to the idea that cognitive academic language proficiency（ CALP） is common across languages, and can therefore easily be transferred from first language use to second language use by the learner.
Ioup, Boustagui, El Tigi & Moselle（ 1994） examined the linguistic competence of an adult second language learner of Egyptian Arabic, who was first exposed to the target language after the end of the critical period. The participant in this study
had acquired native-like proficiency in an untutored learning context. To determine her level of achievement more exactly, her performance in various linguistic areas was compared to that of both native speakers and a highly proficient, tutored learner of Egyptian Arabic. The results suggested that a reexamination for the critical period hypothesis might be necessary.
Harley & Hart（ 1997）, examined the relationship between language aptitude components and second language outcomes among learners whose intensive second language exposure began at different ages. This empirical study showed the different
learning styles among early and late immersion groups, without agreeing or disagreeing with the existence of the critical/sensitive period hypothesis.
This study presented evidence in support of the view that different cognitive abilities tend to be associated with relative second language success in early and late immersion programs. The eventual second language proficiency outcomes from early
immersion were more closely associated with memory abilities, and later immersion outcomes with analytical language ability.
Regarding the critical ages for acquisition, according to several researchers（ e.g. Ellis, 1994; Long, 1990） acquiring native-like pronunciation is possible until the age of 6 – the final age for arrival and acquisition. On the other hand, native-like
grammatical/morphosyntactical competence should be possible up to the age of 15（ e.g. Patkowski, 1980）. As Selinger（ 1978） proposes, there may be multiple critical/sensitive periods for different aspects of language.
Pinker（ 1994） makes the following note. Acquisition of a normal languag （phonology） is guaranteed for children up to the age of six, is steadily compromised from then until shortly after puberty, and is rare thereafter. Maturational changes in the brain, such as the decline in metabolic rate and the number of neurons during early school-age years, and the bottoming out of the number of synapses and metabolic rate around puberty, are plausible causes（. p. 293） On the other hand, the most recent neurocognitive evidence has indicated the mechanism that manages language in the brain’s system. Ullman（ 2007） argues as follows. In first language, lexical knowledge depends on the declarative memory brain system, which underlies semantic and episodic knowledge, and is rooted in temporal-lobe structures. Grammar in first language relies rather on the procedural memory system, which subserves motor and cognitive skills, and is rooted in frontal/basalganglia circuits. In contrast, evidence suggests that in later-learned second language, learners initially depend largely on declarative memory, not only for lexical knowledge, but also for the use of complex forms. However, with increasing experience second language learners show procedural learning of grammatical rules,
becoming first language-like. Importantly, because the behavioral, computational, anatomical and physiological bases of the two memory systems are reasonably well-understood, including the nature of forgetting of knowledge and skills in these systems, we can make relatively specific predictions about language, including with respect to language attrition.（ p. 9）.
Thus, second language learners are unable to acquire the target language as long as they use the declarative brain memory system for its grammatical rules. As Ullman（ 2007） points out, through experience, second language learners come to make use of the procedural memory system. Neurocognitive researchers have presented these findings as reliable through the use of advanced technology, which makes them persuasive. Given that first language grammar is dealt with in this procedural memory system, the so-called universal grammar（ morphosyntax in practice） or language acquisition device presumably may refer to the process of using the procedural memory system for grammar or language rules. If so, with the possible exception of getting a native-like accent, even adult learners could attain native-like proficiency in their target language if they practise it enough to make the language behavior their automatic routine – like riding a bicycle, which also uses the procedural memory system – and to make the procedural memory system active in utilizing the second language’s mophosyntax/grammar. The maxim that practice makes perfect may hold true for acquiring a second language. In the case of child learners, or learners before the age of 15, the procedural memory system rather than the declarative memory system is more likely to be used for second language grammar. Possibly a lack of plasticity in the brain’s system may lead to difficulty in acquiring second languages when we are older. Regarding the subtle distinction between a ‘critical’ and a ‘sensitive’ period, the question is whether completely successful acquisition is deemed to be only possible within a given span of a learner’s life（ critical）, or whether acquisition is just easier within this period （sensitive）.
In Burstall’s study（ 1975）, at the age of 16, the older group still outperformed the younger one. His study shows that age is less important and that the more sophisticated cognitive or possibly academic skills they had in their first language played a more meaningful role in their second language acquisition, except in
the area of listening, which may be biological and less influenced by external factors.
Long（ 1990）, on the other hand, concludes that a neurological explanation is best and proposes a ‘mental muscle model’, where the language-specific faculty remains intact throughout our lives, but access to it is impeded to varying degrees and impeded progressively with age, unless the faculty is used and so kept plastic. Such a view is compatible with studies of exceptional language learners, which demonstrate that some adult learners are capable of achieving native-speaker levels of competence, as seen in the study by Ioup, et al.（ 1994）. As Birdsong（ 1992） points out, the critical/sensitive period hypothesis may have to be reexamined if many such learners are found.
All those who possess a first language are certainly capable of acquiring some degree
of a second language; however, second language acquisition in a mature human is not as successful as first language acquisition in many cases. Although some researchers（ e.g. Bley-Vroman, 1988） have argued that older learners no longer have access to
their innate language acquisition device, consisting of the principles of universal grammar （Chomsky, 1981） and language-specific learning procedures, it has been found to be possible for adult learners to activate such a device by using the procedural memory system（ Ullman, 2007） instead of using the declarative memory system, by following the innate grammatical structure while using the language, and by thorough practice until the structure is internalized in the learners’ minds and
becomes automatic in their behavior. Ullman（ 2001） suggests that ‘an increasing amount of experience（ i.e. practice） with a second language should lead to better learning of grammatical rules in procedural memory, which in turn should result in
higher proficiency in the language’（ p.118）. Even in adult language learning, which has usually been achieved through first language knowledge, so-called universal grammar may be accessible to adult second language learners, but their second
languages are eventually acquired only if they are encouraged to use the procedural memory system instead of the declarative memory system.