Introduction
In the modern linguistics discourse, scholars and practitioners identify multiple factors affecting second-language (L2) acquisition. Age of learning and length of residence in the country of the L2 origin may be considered as the most significant. For example, the critical period theory suggests that individuals tend to acquire L2 skills during early childhood far better, and the learning process usually slows down and becomes more challenging after the transitional developmental period comes to an end, and the brain becomes biologically mature (Huang, 2014). At the same time, it is considered that such a learning technique as language immersion, which implies that a person resides abroad and communicates with native speakers on a daily basis, substantially accelerates the learner’s progress. Therefore, some researchers hypothesise that a higher length of residence is correlated with better language skills (White, 2015).
In the given paper, the introduced variables will be analysed in relation to L2 phonetics and phonology. It is possible to say that the acquisition of L2 phonetics skills and achievement of vowel and consonant harmony may be extremely challenging especially for those students whose first language (L1) phonetic system drastically differs from the L2. However, it can be suggested that the lower age of learning and higher residence length can have a robust effect on the acquisition of L2 sound system in learners. To support this suggestion, several scholarly papers will be reviewed, and major controversies pertinent to the topic will be identified.
Literature Review
Age of Learning
It seems when a person acquires particular skills during early childhood, the chance that he or she will be able to achieve proficiency in whatever they started to do and learn early is much higher than in people who engaged in self-development later in life. The given statement is supported by Berken, Gracco, Chen, and Klein (2016) who revealed the links between learners’ age and the level of language proficiency in them when analysing experience-dependent neural plasticity, as well as structural and functional alterations in the brain, in bilingual individuals with accented and non-accented L2 speech. It is observed that after six months after birth, infants become unable to differentiate phonemes of other languages (Berken et al., 2016).
The given finding implies that inability to achieve a native-like level of proficiency in L2 sound system operation is linked to some developmental, physiological processes. As the researchers state, the thicker accents in young learners are correlated with “age-related constraints on the plasticity of the motor and auditory systems” (Berken et al., 2016, p. 3591). It is implied that the earlier children are exposed to different languages, the greater capacity to understand other languages they obtain. When Berken et al. (2016) compared grey-matter density in simultaneous and sequential bilinguals, it was significantly increased in the left putamen area in the former. As researchers state, the left putamen plays a vital role in language production and motor programming and articulatory coding, in particular. It means that early exposure to the L2 can even change the structure of the brain resulting in better L2 phonologic and phonetic abilities.
The findings obtained by Berken et al. (2016) verify the major propositions in the critical period theory. However, based on these observations, is it appropriate to conclude that adult learners will never be able to succeed in the acquisition of L2 sound system as much as younger learners? According to Abrahamsson (2012), the available research evidence provides rather controversial answers to this question. While some scholars consider that postpuberty learners can show native-like proficiency in L2 phonetics and phonology, others believe that adults can never exhibit such learning outcomes. As Abrahamsson (2012) states, the difference in results between early and late learners can be defined by the fact that they acquire the L2 through distinct brain mechanisms − “children acquire the language (more) implicitly as an interdependent whole, whereas adults learn it (more) explicitly as independent parts of a whole” (p. 187). Since the need for explicit learning increases in adults, the quality and quantity of L2 input become more important factors of progress in them (Granena & Long, 2013).
According to Kissling (2015), adults can still attain a proficiency level yet the approach to phonetics instruction plays a significant role in their case. Nowadays, educational settings usually focus on L2 sound production tasks rather than sound perception. However, as Kissling (2015) states that the understanding of how acoustic and phonemic perception functions is key to effective learning in distinct age groups. Infants and adults perceive language sounds differently. While infants mainly process acoustically and phonetically (in a “continuous” mode) and then gradually shift towards more phonemic (“categorical”) processing, in adults, phonemic/categorical speech processing prevails in any language even when their L2 phonological awareness is imperfect (Kissling, 2015, p. 255). It means that adults use the same phonemic categories, which they have developed in the L1, to process the L2. In this way, it is essential to activate continuous/phonetic processing mode in adult learners to let them differentiate subtle phonetic differences among even apparently similar L1 and L2 sounds. In this way, Kissling (2015) suggests, to acquire L2 sound system, adult learners should first discern between sounds in native and non-native sounds, and then develop “appropriate selective perceptual routines to ‘hear’ them reliably” (p. 256).
Overall, the ideas suggested by Kissling (2015) can be explained by the interaction hypothesis. From the given theoretical perspective, the effects of age on L2 acquisition are defined by the intensity of L1 and L2 interactions in the human mind at distinct developmental stages. L1 phonological categories are more developed in adults and, therefore, the interaction between L1 and L2 categories is more intense in them than in children (Darcy & Krüger, 2012). Since L1 phonological categories are still evolving in children, they usually do not interfere with the acquisition of L2 speech skills. Thus, children are capable of perceiving and producing L2 sounds more accurately. Still, it would be inadequate to presume that adult learners cannot achieve excellent result in the acquisition of L2 sound system just because it is more challenging for them. However, a large portion of available research evidence suggests that the age of exposure to the L2 is still the most significant factor contributing to the level of language proficiency. According to Leung (2012), among immigrants (ages 5-18) in the USA, only those individuals whose L2 acquisition began before the age of 10 attained a native-like level in their speech. It means that childhood and early adolescence may be critical periods in L2 acquisition. When the findings are applied to L2 sound system, those people who start learning non-native languages at later stages in life usually have thicker accents.
However, some researchers provide rather a controversial evidence regarding the impact of age of onset on learners. For example, Casillas and Simonet (2016) investigated how early and late fluent L2 (English) speakers differentiate /æ/–/ɑ/ vowel contrasts in the southwestern dialect. The researchers compared the results in two sample groups comprised of individuals who became dominant in their L2 and completely or partially lost their L1 communicative abilities (early speakers) and those who were dominant in L1 (late speakers). The researchers did not find a significant difference between the two groups. Moreover, it was found that both switched-dominance speakers/early learners and later L2 learners did not attain the same level of English pronunciation proficiency as monolingual speakers − “neither of the two learner groups displayed as much crispness in the phoneme boundary between the /æ/–/ɑ/ contrast as the monolingual English listeners” (Casillas & Simonet, 2016, p. 190). At the same time, both groups of learners showed the same level of ability to differentiate the vowel contrasts as the native speakers did.
All of the studies reviewed in the given section provide different ideas about age effects on L2 production and perception. It is possible to say that they complement each other. Berken et al. (2016) defined how age affects L2 acquisition on the physiological level, while Kissling (2015) focused on the underlying cognitive mechanisms. Casillas and Simonet (2016) provided an empirical evidence, and although it was not very much consistent with the findings of other researchers because it did not show difference in perception and production of L2 sounds by early and late learners, it helped take a look at how other variables, such as language dominance, can interact with learners’ age.
It is possible to say that language dominance is also correlated with learners’ length of residence. Studying or just staying abroad, people need to communicate with native speakers and switch to their L2 and use it more often than the L1. It is also considered that a prolonged stay in the target language country can stimulate phonetic accommodation − “the process in which a talker takes on acoustic characteristics of another individual as a result of exposure to his or her speech” (Zając, 2013, p. 19). Only this can contribute to the improvement of L2 phonetics and phonologic proficiency. However, some other factors may influence the outcomes as well, and they will be discussed along with the length of exposure/residence in the following section.
Length of Residence
Length of residence/immersion into L2 environment is considered an essential variable contributing to learners’ speech improvement. At first glance, it seems to be true because learning is a lifelong process and, when being exposed to the L2, individuals can learn both implicitly (i.e., observing and communicating with native speakers) and explicitly (i.e., deliberately and consciously practising). The variable of the length of residence applies to both early and late learners, immigrants or students participating in exchange programs, etc.
Overall, it is considered that length of residence can impact the perception accuracy and consequently lead to production accuracy (Isbell, 2016). Yet the evidence provided in the recent scholarly works is not consistent. In one of the recent studies, Avello (2013) investigated the effects of the three-months immersion into L2 environment on students’ phonological development and speech production. One of the purposes of the study was to contribute to the under-investigated field of L2 phonology in the study-abroad discourse. The researcher aimed to estimate the program’s effects on acoustic measurements of voice onset time and vowel quality and duration, error rate scores of phonemic and lexical stress mispronunciations, and students’ assessment of foreign accent.
The findings of the study indicate that there was no significant difference between pre-immersion and post-immersion speech production and vowel quality and duration in participants. As Avello (2013) observes, it was especially difficult for learners to pronounce the contrasting vowels /i:-ɪ/ and /æ-ʌ/ correctly as distinct sounds. Neither did the foreign accent improve in students. However, although the quality of vowel production and foreign accent did not change dramatically, the three-months immersion experience contributed to the overall pronunciation accuracy in terms of pronunciation errors. The error rates in “phonemic insertions, deletions, substitutions, and lexical stress misplacement” significantly decreased over this period (Avello, 2013, p. 168). Considering the aims and purposes of the study, it is possible to say that the researcher expanded the understanding of the character and extent of benefits one can get by studying abroad for a short time.
Is it possible to presume that, with a longer period of immersion, one can achieve better L2 speech outcomes? The findings of the literature review conducted by Grimaldi et al. (2014) reveal that late students can largely benefit from long-term (several years) immersion experience in terms of L2 sounds perception. As researchers observe, as a result of such an experience, adult late learners show a better perception of L2 category-boundary vowel contrasts and manage to attain a native-like level while, in students deprived of an opportunity to study in L2 context, the results were much worse. Grimaldi et al. (2014) state that the positive results due to the constant exposure to L2 environment are that it allows forming new long-term native-like memory traces. Moreover, the researchers observe that for the perception improvements in children, a shorter term of L2 exposure is required (about three months). The evidence may indicate the links between the variables “age of learning” and “length of residence/immersion”.
Nevertheless, the age of learning is not the only variable that can be correlated with the length of residence. For instance, Silveira (2012) notes that the quality of input, i.e., the intensity of L2 practice, during the exposure to the L2 is significant for adult late learners. The results of her review of one of the studies showed that Chinese speakers participating in undergraduate and graduate programs in the United States became more proficient in English as they lived in the country longer. At the same time, for Chinese non-students who were merely involved in research work at the university, the outcomes were not the same because they did not practice their L2 skills deliberately and were exposed to English to a lesser degree. The empirical data obtained by Silveira (2012) is consistent with the one she found in other studies. The researcher examined how various internal and external factors affect Brazilian learners’ pronunciation of English consonants especially those in word-final position.
For Brazilian Portuguese speakers it constitutes the major pronunciation difficulty because, compared to English, in this language, only a few consonants are placed in syllable-final positions: “[r] and its allophones, the lateral [l], the nasals [m], [n], and [ŋ], and the sibilants [s] and [z]” (Silveira, 2012, p. 15). Nevertheless, the given sounds, when placed in the word-final position, are often deleted in speech due to the “phonological weakening processes” − “[r] tends to be deleted (comer ‘eat’ [ko’me]); [l] is generally vocalized and realized as the glide [w] (mal ‘bad’ [maw]);” etc. (Silveira, 2012, p. 15). Due to these differences in L1 and L2 phonetics, Brazilian speakers tend to weaken word-final consonants in English as well. Yet, as the researcher found out, students who were exposed to English longer, managed to decrease the rate of common pronunciation errors. However, the results showed that L2 proficiency variable affects phonological process use most. Thus, along with being exposed to the L2 for a significant time, learners should have a rich L2 input to achieve progress.
In the modern scholarly literature, it is most frequently stated that “length of residence in the country is a poor predictor of foreign accent compared to learners’ age of arrival” (Nagle, 2013, p. 149). Additionally, Borges (2014) states that a longer exposure in a target language context does not result in either greater phonological accuracy or consistency. Moreover, the researcher did not find significant associations between the continual use of the L2 and better sound production. However, the factor of L2 proficiency was found to be key to pronunciation. It means that the quality of input is more crucial than the quantity in the development of skills regarding L2 phonology and phonetics.
It is possible to conclude that the effect of the length of residence variable can be modified by other variables of social and psycho-emotional character. As stated by Eslami and Ahn (2014), “learners’ emotional and social attachment to the target language culture has a positive effect on the amount of language learned” (p. 10). Moreover, when a person intends to stay in the target language country for a significant time, he or she is likely to develop extensive contacts with locals, in this way, promoting L2 learning. At the same time, such variables as language shock, culture shock, culture stress, integrative or instrumental motivation, and ego-permeability can be detrimental to L2 sound system acquisition (Eslami & Ahn, 2014). Thus, individual characteristics and attitudes are usually more important than the length of residence itself.
Future Research Recommendations
According to Ader and Miljan (2015), traditionally, internal/neuro-cognitive factors and the external/social ones are strictly divided based on their considered effects on L2 acquisition. Nevertheless, the review of the literature pertaining to the impacts of the learning age and the residence length on individuals’ development of L2 phonetic/phonologic skills reveals that these factors can be deeply interrelated. Therefore, it is important to research different types of factors together.
In many recent studies, the age and length of residence variables were moderated by the level of L2 learners’ proficiency. For instance, Olsen (2016) observes that the variable contributes to better perceptual discrimination of rhotic consonants, alveolar taps, trills, stops, and affricates in L2 learners of Spanish. In its turn, language proficiency can be defined either by their language aptitude, motivations, or the quality of input.
Hu et al. (2013) define language aptitude as “a largely innate, relatively fixed talent for learning language,” which is considered to be “independent of other cognitive abilities, including intelligence” (p. 366). The aptitude constructs relevant to phonetics/phonology competence include the ability to discern sounds, form associations between those sounds and the symbols representing them, and memorise these associations (Hu et al., 2013). It is possible to presume that individuals with low language aptitude will likely not be able to mimic speech sounds and remember them no matter how long they can be exposed to L2 environment. Moreover, insufficient aptitude can significantly slow down the progress of early learners. Thus, it is essential to consider the given cognitive factor in the study of effects of age and length of exposure on L2 sound system acquisition as it may significantly bias the research outcomes if not taken into account.
Conclusion
The findings of the literature review revealed that the age of learning variable is more significant than the length of residence/immersion variable regarding L2 phonetics/phonology competence development. At the same time, the majority of researchers tend to regard early age as a critical factor for the attainment of the native-like speech free of accent. Thus, the critical period theory remains dominant in the modern linguistics discourse as it provides extensive explanation of physiological processes underlying L1 and L2 skills acquisition and is substantially supported by empirical data. The hypothesis emphasises the importance of starting L2 acquisition process early in life. However, the major con of the theory is that it does not show the ways for adults to improve their L2 skills.
Another important theory discussed in the paper was the interaction hypothesis, which suggests that the L1 phonological categories are more developed in adults and, therefore, the interaction between L1 and L2 categories is more intense in them than in children. The advantage of the given theory is that it contains some practical implications. Based on this hypothesis, it is essential to develop an acoustic/phonetic processing in adults to improve their L2 phonemic/categorical perception and production.
When speaking of the length of residence, if studied alone, it proved to have weak effects on L2 learners’ perception and production abilities. However, in correlation with the variables of language proficiency, age of onset, overall attitudes, etc., it seems to be moderately influential. Thus, the further study of L2 proficiency constructs, such as learners’ aptitudes, can be recommended because it may contribute to a better understanding of L2 sound system acquisition.
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