Critical Stage of Language Acquisition - Assignment Example

Critical Stage of Language Acquisition Introduction Age has been a perennial issue in language acquisition research. Although some speculation on its role appeared in the early literature (e.g. Penfield & Roberts, 1959), it was not until the late 1960s that researchers conducted serious empirical investigation (Singleton, 2001). After a debate that lasted for more than a decade, the field eventually came to the conclusion that, in spite of the advantage of older learners in the initial stage of language acquisition, younger learners do outperform older learners in their ultimate attainment (Patricia, 2009; Harley & Wang, 1997; Hyltenstam & Abrahamsson, 2001, 2003). However, the debate over possible causal factors of this age-related difference has continued. One of the most plausible proposals to date suggests that there is a critical period (CP) in Language acquisition (Patricia, 2009). The CP-based account can be traced back to the Critical Period Hypothesis (CPH) first advanced by Lenneberg (1967) (John, 2008). The CPH deems a particular period between the ages of 2 and 13 as critical, during which language acquisition is successful and after which it becomes less successful or even impossible. Ever since Lenneberg postulated the CPH, a great number of theoretical and empirical studies have been conducted to test its validity. Most researchers have come to agree that the CP does exist in language acquisition. In the field of first language acquisition (FLA), most supporting evidence came from observations of language learners who were denied L1 input during the CP and, subsequently, were never able to successfully acquire a language (Curtiss, 1977, 1988). In the field of SLA, most CP studies have shown that younger learners who commence acquisition within the CP successfully acquire their L2s, while older learners who commence acquisition after the CP fail to do so (Hyltenstam & Abrahamsson, 2001, 2003; Han, 2004). Guided by these findings, the majority of L2 researchers have firmly supported the CP as a determinant of the age-related difference in L2 ultimate attainment. The Critical Period Hypothesis (CPH) The Critical Period (CP) is generally defined as "a time during the life span when some specific experience affects the development of an organism more than at other times" (Colombo, 1982, p. 260). The notion of the CP has been cross-disciplinarily adopted as part of a broad attempt to account for the biological nature of certain innate behaviours of organisms. Its origin can be traced back to ethological studies. Among the various ethological studies of the instinctive behaviours observed in birds, fish, and animals such as dogs, Konrad Lorenz's (1970) work on imprinting has proven to be most influential in laying down foundations for the present CP concept. Most of Lorenz's proposals stemmed from his own observations of avian imprinting among grey geese. In his 1970 paper, "Companions as Factors in the Birds' Environment," Lorenz suggested that birds' instinctive behaviour patterns are imprinted by the environment, and he laid particular stress on the fact that imprinting must occur within a limited time-frame. Lorenz also differentiated imprinting from other general types of learning, on the basis of its inextricable involvement with the innate developmental processes peculiar to each stage of an organism's life. Ever since the CP notion was introduced, it has fascinated scientists from other fields and compelled them to prove its existence in their own areas of specialisation. Hubel and Weisel (cited in Bialystok & Hakuta, 1994), for instance, studied cats and monkeys, and ascertained the existence of a CP by demonstrating that early exposure to visual stimuli is essential if vision is to develop normally. According to their observations, the CP for cats stretches from the age of four weeks to four months, and for monkeys from birth to the end of the first year. Both types of animals become blind when deprived of visual experience during those periods. Given this growing recognition ofthe role played by the CP in the development of a variety of organisms (Colombo, 1982), it was inevitable that attempts would also be made to link the CP notion to human language acquisition. The first attempt was made by Penfield and Roberts (1959) and Lenneberg (1967). Penfield and Roberts (1959), two Canadian neurophysiologists, hypothesised that there is a biological constraint on human language learning. This hypothesis was derived from their observations of the language behaviours of aphasics. They found that when the speech areas in the left hemisphere were damaged, preadolescent aphasics were able to recover their speech without difficulty; those who had passed puberty, however, were not able to do so. The researchers attributed the younger patients' recoveries to the ability of the brain to transfer speech functions from the damaged hemisphere to the undamaged one. On the basis of this finding, they suggested that "a child can learn two or three languages easily before the age of nine to twelve, but after the age of nine, the human brain becomes progressively more stiff and rigid" (Penfield & Roberts, 1959, p. 235). Penfield and Roberts further posited a possible advantage to an early start with L2 learning at the ages of 4 to 6. Lenneberg (1967), in his book titled "The Biological Foundation of Language," specifically introduced the term critical period in the context of language acquisition. He made his own observations of the aphasics and reviewed Basser's (1962) studies. Through analyses of aphasics' losses and recoveries of language functions, Lenneberg found that younger children who suffered from traumatic injuries to the brain easily recovered their language functions, whereas post-pubescents' losses were irreversible. This observation led him to propose that the two hemispheres of the human brain are equipotential for language up to the age of two, but that lateralisation of the language function, which is caused by a loss of brain plasticity, develops progressively in childhood until it attains completion at puberty. Lenneberg specified this period from the age two to puberty as the critical period, during which language can be successfully acquired, and after which it becomes marginal at best. This conceptualisation of the CP has been deemed as the original formulation of the Critical Period Hypothesis (CPH) in language acquisition. The Critical Period in FLA and in SLA Since Lenneberg (1967) postulated the CPH, researchers have tested its validity both theoretically and empirically. Even though debates on the CPH still continue, the majority of studies have yielded evidence for the existence of a CP in both first language acquisition (FLA) and second language acquisition (SLA). The Critical Period in FLA In the field of FLA, it has been shown that children who experience a delay in language acquisition successfully acquire their first language, as long as language acquisition starts prior to the offset of the CP. Mason (1942, cited in Long, 1990) reported that a girl named Isabelle was isolated with her uneducated and mute mother until the age of 6½. Though her language learning was delayed until that time, she attained a normal native-like competence after having been exposed to certain linguistic treatments. A similar case was found with the hearing child of a deaf parent called Jim (Sachs, Bard, & Johnson, 1981). Despite the fact that Jim was isolated with his deaf parent until the age of 3½, there was a rapid development in his language after exposure to normal conversations began. Clearer evidence of the CP in FLA can be found in the cases where environmental deprivation or isolation prior to the putative offset ofthe CP leads to incompleteness of language acquisition. Genie (Curtiss, 1977) is a well-known case that exemplifies this condition. Genie was deprived of any linguistic input from the time she was 1½ years old. After suffering years of severe abuse and almost total isolation, she was found at the age of 13 to be without any language ability. In spite of a seven-year intensive language intervention after her discovery, her acquisition stopped at a level similar to that of a two year-old child. It has been suggested that the passage of the CP made it impossible for Genie to employ language-specific learning and processing mechanisms. Curtiss (1988) reported another case of a linguistically isolated individual named Chelsea. Born with some hearing deficit, Chelsea was misdiagnosed as mentally retarded. It was not until age 31 that she was found to have normal hearing ability with the help of a hearing aid. She then began to receive intensive instruction in English and was able to learn a considerable amount of vocabulary. However, she never developed elementary aspects of the grammar. More evidence of incomplete language acquisition emerges from the work done with congenitally deaf children. Since most deaf children are born to hearing parents, they usually are not exposed to meaningful language input until their deafness has been detected and accepted by their parents as a condition that requires exposure to sign language (Bialystok & Hakuta, 1994). Newport and Supalla (1987) conducted a large-scale study of congenitally deaf children's acquisition of American Sign Language (ASL). The deaf participants in their study were exposed to their first language at varying ages, but all other aspects of their social and cognitive development were standard. All of them were regular and fluent users of ASL, with at least forty years of exposure to it. The participants were divided into three groups: native speakers (those who learned ASL from birth at home), early speakers (those who were first exposed to ASL at school, between the ages of four and six), and late speakers (those who were not exposed to ASL until the age of 12). The participants were tested on their production and comprehension of a variety of structures of ASL syntax and morphology. The results showed that native speakers of ASL performed better than did early learners, and early learners outscored late learners. The latter's acquisition was found to be especially sporadic, irregular, and incorrect. The Critical Period in SLA As the previous section has made clear, the existence of the CP in FLA has found ample support from studies that demonstrate different age effects within and outside the CP - successful language acquisition prior to the offset of the CP and incomplete language acquisition after it. When the CP notion is applied to SLA, however, the issue becomes more complex. Lenneberg (1967) associated the CP notion with FLA, leaving unresolved the matter of how it applies to the context of SLA: Most individuals of average intelligence are able to learn a second language after the beginning of their second decade, although the incidence of language-learning -blocks rapidly increases after puberty. Also automatic acquisition from mere exposure to a given language seems to disappear after this age, and foreign languages have to be taught and learned through a laboured effort. Foreign accents cannot be overcome easily after puberty. However, a person can learn to communicate in a foreign language at the age of forty (p.176). Lenneberg seems to propose that the notion of a CP needs to be applied differently to FLA and SLA. He suggests that given fundamentally different linguistic and cognitive conditions of FLA and SLA, a total loss of capacity is likely in FLA, but not in SLA if learning is not activated within a limited time frame. In other words, in the case of adult L2 learners who are already bound by "the existing matrix for L1 language skills" (Lenneberg, 1967, p. 176), their L2 acquisition may lead to incomplete mastery of the L2, but not to a complete loss of the capability to acquire it. The notion of the CP in SLA, therefore, needs to be understood as such: younger learners who commence L2 acquisition within the CP can acquire an L2 solely from exposure to L2 input, whereas older learners who commence L2 acquisition outside of the CP need to make more conscious and laboured efforts in learning an L2. In this sense, the original connotation of a CP suggested by Lenneberg in the context of FLA cannot be used in SLA; thus, the notion of sensitive period (SP) was introduced. Lamendella (1977) suggested that it is inappropriate to refer to a critical period in connection with SLA, given that the original connotation of a CP was that of an all-or-nothing phenomenon having its abrupt onset and offset. He instead proposed a more apt term for SLA: the sensitive period (SP). The SP is generally defined as "a time of heightened responsiveness to certain kinds of environmental stimuli" (Oyama, 1979). In contrast to the original notion of the CP that is marked by its rigidity and abruptness, the SP is characterised by less abrupt changes and by more gradual increases and/or declines (Immelmann & Suomi, 1981). A similar distinction was also made by Patkowski (1980). He stipulates for FLA that since the age limitation is absolute, any adequate acquisition of human language is impossible after a limited-time frame. In other words, no linguistic proficiency can be acquired except for the learning of communication strategies via cognitive mechanisms. By contrast, in the case of SLA where the age limitation is not absolute, L2 learners' failure is only partial. L2 learners attest to a limited ability to achieve a native-like proficiency. Thus, Patkowski advocated the use of critical period for FLA and sensitive period for SLA. Consequently, the notion ofthe CP in SLA must be differentiated from that in FLA. The notion of a CP inherently implies a marked qualitative change in learning capacity at a particular stage of maturation (Singleton, 2003). However, SLA is not an all-or- nothing phenomenon. Therefore, the CPH cannot apply to SLA as it does to FLA. A number of L2 researchers have shown a preference for the notion of sensitive period in SLA, since it accounts for the critical period effects in SLA more accurately (Oyama, 1979). In SLA literature, the term critical period in SLA has been consistently used as a broader and more all-encompassing one that embraces the SP notion. Empirical Evidence of the CP in SLA A number of studies have been conducted in order to ascertain the existence of the CP in SLA. Although the initial evidence for the CP was reported by studies in FLA, the difficulties of directly testing the CPR with L1 learners gave rise to more empirical studies in the context of SLA (Johnson & Newport, 1989). Two major linguistic areas of focus in L2 research have been phonology and syntax. In earlier stages of research, most studies focused on phonology; more recently, however, attention has shifted to morphosyntax. In this section, the major research findings from these two linguistic areas will be presented. Phonology The initial interest in phonology was based on the two prevailing assumptions: 1) phonology was considered the linguistic domain most susceptible to maturational effects, since pronunciation depends, to a large degree, on the neuromuscular apparatus (Scovel, 1988) and 2) phonology was deemed to be the most examinable subsystem of a language, whereas there was no clear way to measure the acquisition of other linguistic domains such as syntax or semantics (Seliger, 1978). Guided by these assumptions, most early CP studies sought to establish whether a native-like accent could be attained within the CP. One of the earliest studies to support the presence of the CP in L2 phonology was carried out by Asher and Garcia (1969). These researchers gave the tasks of sentence pronunciation to 71 Cuban immigrants who had arrived in the United States (U.S.) between the ages of 1 and 19, with all of them having resided in the U.S. for at least five years. Participants who had arrived in the U.S. between the ages of 1 to 6 were rated as near-native speakers and those who had arrived between the ages of 7 and 12 and between the ages of 13 and 19 were identified as having stronger non-native accents. Another study by Seliger, Krashen, and Ladefoged (1975) investigated the impact of age of arrival (AoA) on immigrants' accents. A survey was administered to 394 adult immigrants to the U.S. and to Israel. The participants were divided into three groups by their AoAs: age 9 or younger, between 10 and 15, and 16 or older. The results showed that; 1) the participants of age of 9 or younger retained no foreign accent; 2) the participants between the ages of 10 and 15 displayed a noticeable variability in the presence and absence of foreign accents, and 3) the participants of age 16 or older generally retained an accent. In a study of 60 Italian immigrants to New York City, Oyama (1978) also reported foreign accents in late arrivals' speech. Her participants had come to the city between the ages of 6 and 20, with their length of residence (LoR) being between 5 and18 years. Native English speakers rated the participants' pronunciation that was elicited with via short paragraph readings. A 5-point scale was used with a score of 1 signifying a native-like accent. It was found that the group at ages of 6 -10 scored 1.3; the group at ages of 11-15, 2.4, and the group at ages of 16-20, 3.6. On the basis of this finding, Oyama postulated a strong relationship between AoAs and accents, but she noted no correlation between LoRs and accents. This finding was confirmed by Patkowski's (1990) study of67 U.S. immigrants who had various L1 backgrounds and whose LoR was between 5 and 50 years. Additional evidence for the existence of the CP in phonology was also offered by subsequent studies conducted in late 1970s and early 1980s (e.g., Fathman 1975; Tahta, Wood, & Lowenthal, 1981). The chief methodological characteristic of the CP research in phonology was typified by native speakers' intuitive judgment on participants' overall L2 pronunciation. Deviating from this major strand of research, Williams (cited in Bialystok & Hakuta, 1994) examined the CP effects on specific phonological properties of SLA. She investigated Spanish native speakers' acquisition of two phonemes of English, p and b. Spanish and English differ in that they have different boundaries between the two phonemes along a Voice Onset Time (VOT) continuum. In order to investigate age effects on the two phonemes, the researcher divided the participants into two groups: those who arrived in the U.S. prior to puberty (i.e. at the ages of 8 to 10) and those who arrived in the U.S. after puberty (i.e. at the ages of 14 to 16). Williams not only found a greater shift in the phoneme boundary for English sounds than for Spanish ones, but also noted that the shift occurred more rapidly for the younger group than for the older one. The same results were affirmed by her analysis of the participants' speech production. These findings consistently suggested that younger learners are more sensitive to new L2 phonemes and acquire them more easily than older learners. Likewise, most empirical research, whether on a global or local level, yielded evidence in favor ofthe presence of the CP in L2 phonology. Nonetheless, some researchers held the opposite view (e.g., Bongaerts et al., 1995, 1997) Counter-arguments against the presence of CP effects in L2 phonology mainly derived from research that demonstrated attainment of native-like accents after the closure of the CP. In the so-called training studies, researchers trained and tested post-pubescent speakers to pass for native speakers of the target language (TL). Neufeld's (1977, 1979) was among the most well-known of these training investigations. In his laboratory experiment, Neufeld trained 20 English-speaking Canadian students to pronounce Chinese and Japanese words. After an intensive 12-hour training session in a lab setting, the participants repeated ten short phrases five times. Their final imitation of each phrase was recorded, and three native speaking judges rated participants' accents. Of the 20 participants, one participant received native ratings in both Japanese and Chinese and two participants in Japanese only. Neufeld found that even late L2 learners were still able to attain native-like mastery of the sounds of a foreign language. Neufeld's study, nevertheless, has been subject to several criticisms (Bongaerts, 1999; Long, 1990; Scovel, 1988). A major criticism has been that the participants were trained to imitate or mimic isolated words which do not contain any meaning. This mere mimicking cannot be compared to native speakers' pronunciation in their everyday encounters. It has been also noted that the outcome of the study could well have been affected by the instructions given to the judges. The judges were made to believe that the speech samples were from Japanese and Chinese immigrants whose pronunciation was interfered with due to their L2, English, but not from English native speakers learning Japanese and Chinese. Another attempt to refute the existence of the CP in phonology was made by researchers who sampled advanced L2 learners and measured their performance. Schneiderman and Desmarais (1988), for instance, reported that two native speakers of English who had successfully acquired several foreign languages as adults were judged to originate from French-speaking areas by four native Francophones who listened to short excerpts from tape-recorded interviews with these participants. Ioup et al. (1994) also reported on the success with which their two participants, both native speakers of English, acquired Egyptian Arabic as adults. Tape-recorded spontaneous speech samples from the participants were played to 13 native Arabic-speaking teachers of Arabic as a foreign language. These two participants were rated as native speakers by 8 of the 13 judges. 6 of the 8 judges considered the participants to be native like; 2 judges rated only one participant as a native speaker. Another study was conducted by Bongaerts, Summeren, Planken, and Schils (1995). Three groups of speakers participated: 5 native speakers of British English, 10 Dutch learners of English with an excellent command of British English, and 12 Dutch participants at various levels of proficiency. None of the Dutch participants had been exposed to English prior to the age of 12, either in formal or in informal settings. These participants were assigned four different tasks: (1) a spontaneous speech, (2) reading of brief English texts, (3) reading of 10 sentences, and (4) reading of a list of 25 English words. Their speech-samples were rated by four inexperienced native speakers of British English on a 5-point scale, ranging from very strong foreign accent to no foreign accent at all. The results showed that the judges could not find any difference between the highly successful L2 learners and the native speaker control group. Bongaerts and his colleagues (1997) conducted two studies that replicated the findings of their 1995 studies. In the first replication, they examined learning English as an L2 by Dutch participants (Bongaerts, van Summeren, Planken, & Schils, 1997); in the second replication, they examined learning French as an L2 by Dutch participants (Bongaerts, Mennen, & Vander Slik, 2000). Both studies showed that learners who began L2 acquisition after age 12 could acquire an L2 accent which was judged as native-speakers. What was commonly claimed by the second strand of research is that the native ­likeness observed among late L2 starters can constitute counterevidence to the existence of the CP. This counterevidence, however, has not escaped criticism. First, the number of post-pubescent learners who achieved native-like accents was very limited in number. In addition, for late L2 learners' native-likeness to be counterevidence to the existence of the CP, they must behave like a native speaker in all linguistic domains, not only one linguistic domain (Hyltenstam & Abraharnsson, 2003). Thus, native-likeness reported only in phonology has yet to be tested in other linguistic domains. Furthermore, late L2 learners' native-likeness should be reported in spontaneous communicative settings, not in artificially manipulated settings (DeKeyser & Larsen-Hall, 2005). To summarise, the majority of empirical research supports the existence of a CP in SL phonology by demonstrating native-like accents of younger L2 starters (those who began their acquisition within the CP) and foreign accents of older L2 starters (i.e., those who began their acquisitions after the closure of the CP). With respect to counterevidence to the existence of the CP, researchers have not been able to produce sufficiently convincing evidence to falsify the CP notion. Morphosyntax In an effort to test the CPH in other linguistic domains, CP researchers have also turned their attention to morphosyntax. A number of studies within that domain have supported the existence of the CP. Patkowski (1980), for instance, assessed the syntactic knowledge of 67 non-native speakers of English. He used a trained judge to evaluate written transcripts of the participants' interviews with native controls. The results revealed that non-native speakers who had begun their learning after puberty were given low performance scores by the judges, whereas native speakers and non-native speakers who started learning before puberty scored high. Coppieters (1987) conducted a study that examined advanced L2leamers' knowledge of the TL grammar. He tested 21 highly proficient speakers of French as an L2 by using a written questionnaire that elicited grammatical and semantic judgments. He selected participants who were indistinguishable from native speakers in terms of mistakes and the restricted nature of choices in words and constructions. All of the participants began their language learning as adults. The findings showed that the 21 adult learners of French, many of whom could routinely pass for a native speaker, were clearly distinguishable from native speakers when tested on a variety of syntactic and semantic judgments. Further support for the existence of the CP in L2 morpho syntactic development was provided by Johnson and Newport's study (1989). It has been recognised as a landmark CP investigation due to its clear-cut evidence for the CP. The researchers examined 46 native Koreans and Chinese speakers who arrived in the United States between the ages of 3 and 39 (23 early arrivals came before the age of 15, and 23 late arrivals came after the age of 17) and who had resided in the U.S. for periods ranging from 3 to 26 years. The participants were tested on their knowledge of English syntax and morphology by being asked to judge the grammaticality of spoken English sentences. The test was composed of 276 sentences: 140 were ungrammatical, whereas the other 136 were grammatical. The analysis of the test scores demonstrated that the participants' performance was linearly related to AoAs up to puberty. After puberty, performance was low, but highly variable and unrelated to AoAs. The age effect was shown not to be an inadvertent result of differences in the amount of experience with English, motivation, self-consciousness, or American identification. As shown thus far, most CP studies on morpho syntax have observed behavioural evidence of the existence ofthe CP. However, findings obtained through neurological research have also confirmed the role of the CP in L2 morphosyntax. Kim, Relikin, Kyong-Min, and Hirsh (1997) used magnetic resonance imagining (MRI) to examine the spatial representations of L1 and L2 in the cerebral cortex of early and late bilinguals during a sentence-generation task. Their results demonstrated little or no age-related separation of activity in Wernicke's area, but age-related differences in activity were observed in Broca's area. The late arrivals were shown to use two distinct, yet adjacent centres of activation for Ll and L2, whereas the early bilinguals use a single area of brain activation for both L1 and L2. This finding indicates different kinds of brain organisation in early and late bilinguals. In other words, this neurological result may be interpreted as direct evidence of fundamental differences between children and adults with respect to the language-acquiring/processing mechanisms. Another neurological study was conducted by Weber-Fox and Neville (1999). They used event-related potentials (ERP) to compare the brain activity of Chinese­ English bilinguals whose AoAs varied from 0 to 16. The researchers found significant differences on the semantic processing tasks between native speakers and L2 learners at AoA 11 or older and on syntactic processing tasks between native speakers and L2 learners at AoA 14 or older. Using the same ERP method, Hahne (2001) also found similar effects for Russian-German bilinguals at the AoAs of 10 or older: small differences in semantic processing, but notable ones in syntactic processing. The overall review of CP-related studies, whether behavioural or neurological in nature, reveals substantial evidence for the CP in L2 morphosyntax. However, counterarguments have also been waged, many of which to be found in the area of phonology. The major body of counterevidence in L2 morpho syntax emerges from studies showing the native-like proficiency of older L2 starters who first received exposure to the L2 well after the closure of the hypothesised CP (Birdsong 1992; Birdsong, 1999). For example, Birdsong (1992) examined the acquisition of L2 French by 20 English native speakers who had begun to learn French after puberty. He found that among the 20 participants, 15 fell within the range of the native-like controls on the grammaticality judgment task, and 5 participants deviated insignificantly from native norms. Van Wuigtswinkel (1994) assessed two groups of Dutch native speakers who had begun learning English after the age of 12. The grammaticality judgment test administered to the participants consisted of a subset of Newport's study (1989) items along with an assortment of other syntactic structures. The study found native-like performance in 8 out of 26 participants in one group, and 7 out of 8 participants in the other group. A study by White and Genesee (1996) examined the acquisition of English after the age of 12 by French native speakers. The participants were asked to judge the grammaticality of 60 wh-movement structures. The authors found no significant differences between near ­natives and the native controls on any task. Another argument raised against the CP centres on the fact that there does not appear to be an identifiable change in the shape of the proficiency function at a point which defines the critical period terminus. The change does not have to be abrupt, but there should be a period of heightened performance followed by a gradual decline to a plateau near the offset point which continues to show relatively high performance. The function should be discontinuous at this point. In other words, a discontinuous non-linear relationship across age groups would yield support for the CP, whereas a linear relationship across age groups provides evidence against the CP. This issue is not trivial as some recent studies have rejected the existence of the CP based on the presence of the linear declining relationship between age and performance in their data. For instance, Stevens (1999) examined the data from the 1990 U.S. census. The data, which were reported by the immigrants themselves, were used to assess the degree of English fluency. The researcher concluded that although L2 proficiency was strongly related to the age of immigration, there was no abruptly outlined critical period, but rather a steady decline in performance, with those whose AoA was before age 5 having the highest probability of reporting in adulthood that they spoke the L2 very well. Similarly, Bialystok and Hakuta (1999) using the same 1999 census data found that a continuous age-related declining curve. The data came from Chinese- and Spanish-speaking immigrants residing in New York. The curves for both groups were quite similar, although the Chinese group had lower overall self-reported proficiency. Bialystok and Hakuta concluded from their data that factors other than an innate bioprogram were responsible for the decline. Bialystok and Miller (1999) also employed a grammaticality judgment test with items similar to those of Johnson and Newport's study (1989). Again, there was a steadily declining linear performance function across ages, results not predicted by a biologically defined CP. Birdsong and Molis (2001) undertook a replication of Johnson and Newport's study (1989), using the same methods and materials, but with participants from a very different language background, in this case Spanish. They also found a gradually declining slope exhibiting a strong age effect among the late arrivals. In sum, the research in morpho syntax has, as in the domain of phonology, yielded considerable findings in favor of the existence of the CP. Although a clearer relationship between neurological differences and differences in language proficiency has yet to be established (Singleton, 2003), the majority of findings, both behavioural and neurological, supported the notion of the CP. It is worth noting that evidence against the CP existence remains substantially marginal and is not persuasive enough to invalidate the CP notion. In particular, regarding native-likeness among post-pubescent learners, Scovel (1988) proposed that all natural populations contain exceptions, and the cases of native-like competences among adult SLA learners may well belong to this exceptional population within a standard deviation of plus two or three. He also speculated that there may be some exceptional foreign language learners - about 1 in 1,000, in any population of later starters - who are not bound by the CP constraints. Indeed, some case studies have centred on the phenomenal language learning processes of certain exceptional learners who seem to have retained the neurocognitive flexibility normally found only in younger starters (e.g. Ioup et al., 1994; Schneiderman & Desmarais, 1988). In sum, the counterevidence garnered in the area of syntax has not been substantial enough to outweigh the evidence for the CP. Hence, it seems reasonable to argue that the CP does exist in the area of L2 morphosyntax. In recent years, however, many researchers have cast doubts on the viability of an exclusively CP-oriented interpretation of the age-related difference. There has been a growing consensus that age may be confounded with other variables and that those variables might be the valid causal factors of the child-adult difference in L2 ultimate attainment. That is, it has been acknowledged that age is neither isolatable nor falsifiable and that it is impossible to observe it separately from other concurrent factors. Thus, the age-related phenomenon cannot be fully understood until it is conclusively tested in relation to other factors (Moyer, 2004). Conclusion In light of the above review, we can conclude that the CP plays a leading role in effectuating the difference in the ultimate attainment of younger and older L2 starters. Some CP research has advanced a sophisticated speculation as to the role of the CP in determining the age-related difference (ARD). Among those who favor the existence of the CP, there has been a growing consensus that maturation may not be the sole causal factor of the ARD; indeed, multiple factors confounded with age may interact with the CP and create the ARD (Han, 2004; Singleton, 2001). That is, researchers have acknowledged that the single-factor account cannot fully explain the ARD in L2 ultimate attainment. Singleton (2001) asserted that the phenomenon of the ARD needs to be interpreted in terms of not only neurological maturation, but also a range of other factors. References Asher, J. & Garcia, R. (1969). The optimal age to learn a foreign language. Modern Language Journal, 53, 334-341. Basser, L. S. (1962). Hemiplegia of early onset and the faculty of speech with special reference to the effects of hemispherectomy. Brain, 85, 427-460. Bialystok, E. & Hakuta, K. (1994). In other words: In science and psychology of second language acquisition. New York: Basic Books. Bialystok, E. & Hakuta, K. (1994). In other words: In science and psychology of second language acquisition. New York: Basic Books. Bialystok, E. & Hakuta, K. (1999). Confounded age: Linguistic and cognitive factors in age difference for second language acquisition. In D. Birdsong (Ed.), Second language acquisition and the critical period hypothesis (pp. 161-181). Mahwah, NJ: Erlbaum. Bialystok, E. & Miller, B. (1999). The problem of age in second language acquisition: Influences from language, task, and structure. Bilingualism: Language and Cognition, 2, 127-145. Birdsong, D. & Molis, M. (2001). On the evidence for maturational constraints in second language acquisition. Journal of Memory and Language, 44, 235-249. Birdsong, D. (1992). Ultimate attainment in second language acquisition. Language, 68, 709-755. Birdsong, D. (1999). The introduction: whys and why nots ofthe critical period hypothesis for second language acquisition. In D. Birdsong (Ed.), Second language acquisition and the critical period hypothesis (pp. 2-22). Mahwah, NJ: Erlbaum. Bongaerts, T. (1999). Ultimate attainment in L2 pronunciation: The case of very advanced late L2learners. In D. Birdsong (Ed.), Second language acquisition and the critical period hypothesis (pp. 133-159). Mahwah, NJ: Erlbaum. Bongaerts, T., Mennen, S., & Van der Slik, F. (2000). Authenticity of pronunciation in naturalistic second language acquisition. Stuidia Linguistica, 54, 298-308. Bongaerts, T., van Summeren C. V., Planken, B., & Schils, E. (1995). Age and ultimate attainment in the pronunciation of a foreign language. Studies in Second Language Acquisition, 19,447-465. Bongaerts, T., van Summeren, C., Planken, B., & Schils, E. (1997). Age and ultimate attainment in the pronunciation of a foreign language. Studies in Second Language Acquisition, 19, 447-465. Colombo, J. (1982). The critical period concept: Research, methodology, and theoretical issues. Psychological Bulletin, 91,260- 275. Colombo, J. (1982). The critical period concept: Research, methodology, and theoretical issues. Psychological Bulletin, 91,260- 275. Coppieters, R. (1987). Competence differences between native and fluent non-native speakers. Language, 63, 544-573. Curtiss, S. R. (1977). Genie: A linguistic study of a modern day "wild child. " New York: Academic Press. Curtiss, S. R. (1977). Genie: A linguistic study of a modern day "wild child. " New York: Academic Press. Curtiss, S. R. (1988). Abnormal language acquisition and the modularity of language. In F. J. Newmeyer (Ed.), Linguistics: The Cambridge survey (pp. 96-116). Cambridge, UK: Cambridge University Press. Curtiss, S. R. (1988). Abnormal language acquisition and the modularity of language. In F. J. Newmeyer (Ed.), Linguistics: The Cambridge survey (pp. 96-116). Cambridge, UK: Cambridge University Press. DeKeyser, R. & Larsen-Hall, J. (2005). What does the critical period really mean? In J. E. Kroll & A. M. B. De Groot (Eds.), Handbook of bilingualism: Psycholinguistic approaches. Oxford: Oxford University Press. Fathman, A. (1975). The relationship between age and second language productive ability. Language Learning, 25, 245-253. Hahne, A. (2001). What's the difference in second-language processing?: Evidence from event-related brain potentials. Journal of Psycholinguistic Research, 30, 251-266. Han, Z-H. (2004). Fossilization in adult second language acquisition. Tonawanda, NY: Multilingual Matters LTD. Harley, B. & Wang, W. (1997). The critical period hypothesis: Where are we now? In de Groot, A. & Kroll, J. (Eds.), Tutorials in bilingualism (pp.l9-51). Mahwah: Lawrence Erlbaum Associates. Hyltenstam, K. & Abrahamsson, N. (2001). Age and L2learning: The hazards of matching practical "implications" with theoretical "facts". TESaL Quarterly, 35, 151-170. Hyltenstam, K. & Abrahamsson, N. (2003). Maturational constraints in second language acquisition. In C. Doughty & M. Long (Eds.), Handbook of second language acquisition (pp. 539-588). Oxford, UK: Blackwell. Hyltenstam, K. & Abrahamsson, N. (2003). Maturational constraints in second language acquisition. In C. Doughty & M. Long (Eds.), Handbook of second language acquisition (pp. 539-588). Oxford, UK: Blackwell. Immelmann, K. & Suomi, S. J. (1981). Sensitive phases in development. In K. Immelmann, G. W. Barlow, L. Petrinovich, & M. Main (Eds.), Developmental psycholinguistics: Theory and applications: Georgetown round table on language and linguistics (pp. 395-431). Washington DC: Georgetown University. Ioup, G., Boustagui, E., EI tigi, M., & Moselle, M. (1994). Reexamining the critical period hypothesis: A case study of successful adult SLA in a naturalistic environment. Studies in Second Language Acquisition, 16, 73-98. John, P. (2008). Critical Period Hypothesis. Encyclopedia of Bilingual Education. SAGE Publications. Johnson, J. S. & Newport, E. L. (1989). Critical period effects in second language 1eaming: The influence of the maturational state on the acquisition of English as a second language. Cognitive Psychology, 21,60-99. Johnson, J. S. & Newport, E. L. (1989). Critical period effects in second language 1eaming: The influence of the maturational state on the acquisition of English as a second language. Cognitive Psychology, 21,60-99. Kim, K. H. S., Relikin, N. R., Kyong-Min, L., & Hirsh, J. (1997). Distinct cortical areas associated with native and second languages. Nature, 388, 171-174. Lamendella, J. (1977). General principles of neurofunctional organization and their manifestation in primary and non-primary acquisition. Language Learning, 27, 155-196. Lenneberg, E. H. (1967). Biologicalfoundations of language. New York: Wiley. Long. M. H. (1990). Maturational constraints of language development. Studies in Second Language, 12,251-285. Lorenz, K. (1970). Comparisons as factors in the bird's environment. In K. Lorenz (Ed.), Studies in animal and human behaviour (Vol. 1). Cambridge, Mass: Harvard University Press. Moyer, A. (2004). Age, accent, and experience in second language acquisition. Buffalo, NY: Multilingual Matters LTD. Neufeld, G. (1977). Language learning ability in adults: A study on the acquisition of prosodic and articulatory features. Working Papers on Bilingualism, 12, 45-60. Neufeld, G. (1979). Towards a theory of language learning ability. Language Learning, 29, 227-241. Newport, E. L. & Supalla, T. (1987). A critical period effect in the acquisition of a primary language. University of Illinois. Oyama, S. C. (1978). The sensitive period and comprehension of speech. Working Papers on Bilingualism, 16, 1-17. Oyama, S. C. (1979). The concept ofthe sensitive period in developmental studies. Merrill-Palmer Quarterly, 25,83-103. Patkowski, M. (1980). The sensitive period for the acquisition of syntax in a second language acquisition. Language Learning, 30,449-472. Patkowski, M. (1990). Age and accent in a second language: A reply to James Emil Flege. Applied Linguistics, 11, 73-89. Patricia, E. (2009). Critical Period Hypothesis. Encyclopedia of Time: Science, Philosophy, Theology, & Culture. SAGE Publications. Penfield, W. & Roberts, L. (1959). Speech and brain mechanisms. New York, NY: Atheneum Press Sachs, J., Bard, 8., & Johnson, M. L. (1981). Language learning with restricted input: Case studies of two hearing children of deaf parents. Applied Psycho linguistics, 2, 33-54. Schneiderman, E. & Desmarais, C. (1988). The talented language learner: Some preliminary findings. Second Language Research, 4, 91-109. Scovel, T. (1988). A time to speak: A psycholinguistic inquiry into the critical period for human research. Cambridge, MA: Newbury House. Seliger, H. (1978). Implications of a multiple critical periods hypothesis for second language learning. In W. Ritchie (Ed.), Second language acquisition research: Issues and implications (pp. 11-19). New York, NY: Academic Press. Seliger, H. W., Krashen, S. D., & Ladefoged, P. (1975). Maturational constraints in the acquisition of second language acquisition. Language Science, 36, 20-22. Singleton, D. (2001). Age and second language acquisition. Annual Review of Applied Linguistics, 21, 77-89. Singleton, D. (2003). Critical period or general age factor(s)? In M. Mayo & M. Lecumberri (Eds.), Age and the acquisition of English as a foreign language (pp. 3-22). Buffalo, NY: Multilingual Matters LTD. Stevens, G. (1999). Age at immigration and second language proficiency among foreign born adults. Language in Society, 28, 555-578. Tahta, S., Wood, M., & Loewenthal, K. (1981). Foreign accents: Factors relating to transfer of accent from the first language to a second language. Language and Speech, 24, 265-272. Van Wuigtswinkel, K. (1994). Critical period effects on the acquisition of grammatical competence in a second language. Katholieke Universiteit, Nijmegen. Weber-Fox, C. M. & Neville, H. J. (1999). Functional neural subsystems are differentially affected by delays in second-language immersion: ERP and behavioural evidence in bilingual speakers. In D. Birdsong (Ed.), Second language acquisition and the critical period hypothesis (pp. 23-38). Mahwah, NJ: Erlbaurn. White, L. & Genesee, F. (1996). How native is near-native?: The issue of ultimate attainment in adult second language acquisition. Second Language Research, 12, 238-265. Read More