critical age hypothesis second language acquisition

Last updated 27/06/24: Online ordering is currently unavailable due to technical issues. We apologise for any delays responding to customers while we resolve this. For further updates please visit our website: https://www.cambridge.org/news-and-insights/technical-incident

We use cookies to distinguish you from other users and to provide you with a better experience on our websites. Close this message to accept cookies or find out how to manage your cookie settings .

Login Alert

• > Journals
• > Bilingualism: Language and Cognition
• > Volume 21 Issue 5
• > Critical periods for language acquisition: New insights...

Article contents

Critical periods for language acquisition: new insights with particular reference to bilingualism research.

Published online by Cambridge University Press:  23 October 2018

One of the best-known claims from language acquisition research is that the capacity to learn languages is constrained by maturational changes, with particular time windows (aka ‘critical’ or ‘sensitive’ periods) better suited for language learning than others. Evidence for the critical period hypothesis (CPH) comes from a number of sources demonstrating that age is a crucial predictor for language attainment and that the capacity to learn language diminishes with age. To take just one example, a recent study by Hartshorne, Tenenbaum and Pinker ( 2018 ) identified a ‘sharply-defined critical period’ for grammar learning, and a steady decline thereafter, based on a very large dataset (of 2/3 million English Speakers) that allowed them to disentangle critical-period effects from non-age factors (e.g., amount of experience) affecting grammatical performance. Other evidence for the CPH comes from research with individuals who were deprived of linguistic input during the critical period (Curtiss, 1977 ) and were consequently unable to acquire language properly. Moreover, neurobiological research has shown that critical periods affect the neurological substrate for language processing, specifically for grammar (Wartenburger, Heekeren, Abutalebi, Cappa, Villringer & Perani, 2003 ).

One of the best-known claims from language acquisition research is that the capacity to learn languages is constrained by maturational changes, with particular time windows (aka ‘critical’ or ‘sensitive’ periods) better suited for language learning than others. Evidence for the critical period hypothesis (CPH) comes from a number of sources demonstrating that age is a crucial predictor for language attainment and that the capacity to learn language diminishes with age. To take just one example, a recent study by Hartshorne, Tenenbaum and Pinker ( Reference Hartshorne, Tenenbaum and Pinker 2018 ) identified a ‘sharply-defined critical period’ for grammar learning, and a steady decline thereafter, based on a very large dataset (of 2/3 million English Speakers) that allowed them to disentangle critical-period effects from non-age factors (e.g., amount of experience) affecting grammatical performance. Other evidence for the CPH comes from research with individuals who were deprived of linguistic input during the critical period (Curtiss, Reference Curtiss 1977 ) and were consequently unable to acquire language properly. Moreover, neurobiological research has shown that critical periods affect the neurological substrate for language processing, specifically for grammar (Wartenburger, Heekeren, Abutalebi, Cappa, Villringer & Perani, Reference Wartenburger, Heekeren, Abutalebi, Cappa, Villringer and Perani 2003 ).

In bilingualism research, the CPH has received a somewhat mixed response, with some researchers plainly denying that critical periods constrain language acquisition (e.g., Bialystok & Kroll, Reference Bialystok and Kroll 2018 ) and others having ‘little doubt’ that language acquisition is subject to critical period effects (Meisel, Reference Meisel, Boeckx and Grohmann 2013 : 71). It is true that early onsets of bilingual first language acquisition (during childhood) do indeed typically yield better linguistic skills than later ones, in line with the CPH. On the other hand, individuals with early onsets of acquisition of a particular language are typically also younger when they learn that language and have a longer time of exposure than individuals with a later onset of acquisition. Given these potentially confounding factors, supposed critical period effects might be open to alternative interpretations.

Our keynote article (Mayberry & Kluender, Reference Mayberry and Kluender 2018a ) offers a new challenging perspective on the CPH by relying mainly on studies of the acquisition of sign languages, the specific learning circumstances of which offer a unique opportunity to disentangle genuine critical-period effects from non-age factors affecting linguistic performance. Mayberry and Kluender specifically compare linguistic outcomes of the acquisition of sign languages in post-childhood L2 learners with that of post-childhood L1 learners. Their most striking finding is that late L1 learners perform significantly worse in morphology, syntax and phonology than late L2 learners. This contrast appears to be unrelated to non-linguistic cognitive or motivational factors but is attributed instead to very late L1 learners having developed an incomplete brain/language system during childhood brain maturation. L2 learners, on the other hand, have already established a fully-fledged brain/language system during this period. Mayberry and Kluender conclude from the more substantial age-of-acquisition effect in adult L1 than in adult L2 learners that there is a critical period for the acquisition of a first language only, whereas L2 development is affected by other factors.

Fifteen commentaries, most of which were specifically selected to represent different views on the CPH from the perspective of bilingualism research, accompany the keynote article. Many commentators praise the keynote article for drawing attention to the acquisition of sign languages, which through comparisons of late L1 and L2 learners contributes important insights for our understanding of a critical or sensitive period for the acquisition of language. Woll ( Reference Woll 2018 ) reports an additional case of late L1 acquisition of (British) Sign language, a deaf person with very late exposure to L1, who exhibits severe difficulties with syntax and phonology despite intact cognitive skills, in line with the findings reported in the keynote article. On the other hand, Mayberry and Kluender's ( Reference Mayberry and Kluender 2018 a) claim that maturational factors (viz. critical or sensitive periods) do not affect L2 acquisition has received a less positive response from many commentators. Several commentators point to evidence indicating age-of-acquisition effects on L2 speakers’ linguistic skill and to models of L2 acquisition that account for the role of maturational constraints implicated by the CPH (Abrahamsson, Reference Abrahamsson 2018 ; DeKeyser, Reference DeKeyser 2018 ; Hyltenstam, Reference Hyltenstam 2018 ; Long & Granena, Reference Long and Granena 2018 ; Newport, Reference Newport 2018 ; Reh, Arredondo & Werker, Reference Reh, Arredondo and Werker 2018 ; Veríssimo, Reference Veríssimo 2018 ). As opposed to these researchers, some commentators question the role of critical or sensitive periods for language not only for L2 but also for L1 acquisition (Bialystok & Kroll, Reference Bialystok and Kroll 2018 ; Flege, Reference Flege 2018 ). Other commentators highlight specific limitations of the proposed account and of the data presented in its support. Birdsong and Quinto-Pozos ( Reference Birdsong and Quinto-Pozos 2018 ) note that what is missing from Mayberry and Kluender's comparison of late L1 vs. L2 signers is a role for bilingualism, arguing that comparing bilinguals with monolinguals will always reveal differences regardless of the age of L2 acquisition. Emmorey ( Reference Emmorey 2018 ) questions the keynote article's claim that if L2 outcomes were fully under the control of a critical period, they should not be as variable as they are and affected by cognitive or motivational factors, by pointing out that this variability does indeed extend to L1 learners. Lillo-Martin ( Reference Lillo-Martin 2018 ) points out that there may be domain-specific splits with respect to critical periods, with different age cutoffs for different linguistic phenomena, a possibility that is not considered in any detail in the keynote article (see also Veríssimo, Reference Veríssimo 2018 ). Finally, Bley-Vroman ( 2018 ) and White ( Reference White 2018 ) use the evidence presented in our keynote article to address the question of whether or not domain-specific learning mechanisms are available to adult language learners; see also Clahsen & Muysken ( Reference Clahsen and Muysken 1986 ; Reference Clahsen and Muysken 1989 ).

In their response, Mayberry and Kluender ( Reference Mayberry and Kluender 2018b ) highlight points of agreement, clear up misunderstandings, admit current limitations of their proposal, and welcome suggestions for future research. Most importantly, however, in the face of the commentaries Mayberry and Kluender ( Reference Mayberry and Kluender 2018b ) modify their original claim of a critical period for L1 acquisition only. They now sympathize with the idea that there are critical periods for both L1 and L2 acquisition, but with less severe AoA effects on late L2 acquisition than on delayed L1 acquisition, due to L2 speakers having learnt another language early in life; see Hyltenstam ( Reference Hyltenstam 2018 ) and Newport ( Reference Newport 2018 ).

We hope our readers will enjoy the keynote article together with the commentaries and the authors’ response as well as the interesting regular research articles and research notes presented in the current issue.

This article has been cited by the following publications. This list is generated based on data provided by Crossref .

• Google Scholar

View all Google Scholar citations for this article.

Save article to Kindle

To save this article to your Kindle, first ensure [email protected] is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle .

Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

Find out more about the Kindle Personal Document Service.

• Volume 21, Issue 5
• JUBIN ABUTALEBI (a1) and HARALD CLAHSEN (a2)
• DOI: https://doi.org/10.1017/S1366728918001025

Save article to Dropbox

To save this article to your Dropbox account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you used this feature, you will be asked to authorise Cambridge Core to connect with your Dropbox account. Find out more about saving content to Dropbox .

Save article to Google Drive

To save this article to your Google Drive account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you used this feature, you will be asked to authorise Cambridge Core to connect with your Google Drive account. Find out more about saving content to Google Drive .

Reply to: Submit a response

- No HTML tags allowed - Web page URLs will display as text only - Lines and paragraphs break automatically - Attachments, images or tables are not permitted

Your details

Your email address will be used in order to notify you when your comment has been reviewed by the moderator and in case the author(s) of the article or the moderator need to contact you directly.

You have entered the maximum number of contributors

Conflicting interests.

Please list any fees and grants from, employment by, consultancy for, shared ownership in or any close relationship with, at any time over the preceding 36 months, any organisation whose interests may be affected by the publication of the response. Please also list any non-financial associations or interests (personal, professional, political, institutional, religious or other) that a reasonable reader would want to know about in relation to the submitted work. This pertains to all the authors of the piece, their spouses or partners.

• Search Menu
• Sign in through your institution
• Advance articles
• Editor's Choice
• Key Concepts
• The View From Here
• Author Guidelines
• Submission Site
• Open Access
• Why Publish?
• About ELT Journal
• Editorial Board
• Advertising and Corporate Services
• Journals Career Network
• Self-Archiving Policy
• Dispatch Dates
• Terms and Conditions
• Journals on Oxford Academic
• Books on Oxford Academic

Article Contents

• < Previous

Age and the critical period hypothesis

• Article contents
• Figures & tables
• Supplementary Data

Christian Abello-Contesse, Age and the critical period hypothesis, ELT Journal , Volume 63, Issue 2, April 2009, Pages 170–172, https://doi.org/10.1093/elt/ccn072

• Permissions Icon Permissions

In the field of second language acquisition (SLA), how specific aspects of learning a non-native language (L2) may be affected by when the process begins is referred to as the ‘age factor’. Because of the way age intersects with a range of social, affective, educational, and experiential variables, clarifying its relationship with learning rate and/or success is a major challenge.

There is a popular belief that children as L2 learners are ‘superior’ to adults ( Scovel 2000 ), that is, the younger the learner, the quicker the learning process and the better the outcomes. Nevertheless, a closer examination of the ways in which age combines with other variables reveals a more complex picture, with both favourable and unfavourable age-related differences being associated with early- and late-starting L2 learners ( Johnstone 2002 ).

The ‘critical period hypothesis’ (CPH) is a particularly relevant case in point. This is the claim that there is, indeed, an optimal period for language acquisition, ending at puberty. However, in its original formulation ( Lenneberg 1967 ), evidence for its existence was based on the relearning of impaired L1 skills, rather than the learning of a second language under normal circumstances.

Furthermore, although the age factor is an uncontroversial research variable extending from birth to death ( Cook 1995 ), and the CPH is a narrowly focused proposal subject to recurrent debate, ironically, it is the latter that tends to dominate SLA discussions ( García Lecumberri and Gallardo 2003 ), resulting in a number of competing conceptualizations. Thus, in the current literature on the subject ( Bialystok 1997 ; Richards and Schmidt 2002 ; Abello-Contesse et al. 2006), references can be found to (i) multiple critical periods (each based on a specific language component, such as age six for L2 phonology), (ii) the non-existence of one or more critical periods for L2 versus L1 acquisition, (iii) a ‘sensitive’ yet not ‘critical’ period, and (iv) a gradual and continual decline from childhood to adulthood.

It therefore needs to be recognized that there is a marked contrast between the CPH as an issue of continuing dispute in SLA, on the one hand, and, on the other, the popular view that it is an invariable ‘law’, equally applicable to any L2 acquisition context or situation. In fact, research indicates that age effects of all kinds depend largely on the actual opportunities for learning which are available within overall contexts of L2 acquisition and particular learning situations, notably the extent to which initial exposure is substantial and sustained ( Lightbown 2000 ).

Thus, most classroom-based studies have shown not only a lack of direct correlation between an earlier start and more successful/rapid L2 development but also a strong tendency for older children and teenagers to be more efficient learners. For example, in research conducted in the context of conventional school programmes, Cenoz (2003) and Muñoz (2006) have shown that learners whose exposure to the L2 began at age 11 consistently displayed higher levels of proficiency than those for whom it began at 4 or 8. Furthermore, comparable limitations have been reported for young learners in school settings involving innovative, immersion-type programmes, where exposure to the target language is significantly increased through subject-matter teaching in the L2 ( Genesee 1992 ; Abello-Contesse 2006 ). In sum, as Harley and Wang (1997) have argued, more mature learners are usually capable of making faster initial progress in acquiring the grammatical and lexical components of an L2 due to their higher level of cognitive development and greater analytical abilities.

In terms of language pedagogy, it can therefore be concluded that (i) there is no single ‘magic’ age for L2 learning, (ii) both older and younger learners are able to achieve advanced levels of proficiency in an L2, and (iii) the general and specific characteristics of the learning environment are also likely to be variables of equal or greater importance.

Google Scholar

Google Preview

Email alerts

Citing articles via.

• Recommend to Your Library

Affiliations

• Online ISSN 1477-4526
• Print ISSN 0951-0893
• Copyright © 2024 Oxford University Press
• About Oxford Academic
• Publish journals with us
• University press partners
• What we publish
• New features  
• Open access
• Institutional account management
• Rights and permissions
• Get help with access
• Accessibility
• Advertising
• Media enquiries
• Oxford University Press
• Oxford Languages
• University of Oxford

Oxford University Press is a department of the University of Oxford. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide

• Copyright © 2024 Oxford University Press
• Cookie settings
• Cookie policy
• Privacy policy
• Legal notice

This Feature Is Available To Subscribers Only

Sign In or Create an Account

This PDF is available to Subscribers Only

For full access to this pdf, sign in to an existing account, or purchase an annual subscription.

An official website of the United States government

The .gov means it’s official. Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

The site is secure. The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

• Publications
• Account settings

Preview improvements coming to the PMC website in October 2024. Learn More or Try it out now .

• Advanced Search
• Journal List
• HHS Author Manuscripts

What Does a Critical Period for Second Language Acquisition Mean?: Reflections on Hartshorne, Tenenbaum, and Pinker (2018)

Arturo E. Hernandez was the lead author and worked on all aspects of the manuscript. Jean Bodet was involved in the revision and the incorporation of Neuroemergentist models of language development. Kevin Gehm and Shutian Shen worked on the description of the previous work by Hartshorne and colleagues.

Hartshorne, Tenenbaum and Pinker (2018) used a very large sample in order to disentangle the effects of age, years of experience, and age of exposure from each other in context of second-language acquisition. Participants were administered an online test of English grammar. Results revealed a critical period ending around 17 years of age for the most effective acquisition of a second language (L2). The findings of a late cutoff indicate the age range of late childhood to late adolescence as crucial for learning an L2. In this piece, we argue that these results can be conceptualized by emergentist models of language acquisition in which both behavior and brain interactively reorganize across development.

Introduction

Hartshorne, Tenenbaum, and Pinker (2018) , henceforth HTP, present evidence for a critical period of second-language (L2) syntax acquisition that extends into late adolescence, only declining around the age of 17. We, as well as HTP, have come to the conclusion that the proposed critical period may be representative of a change in a behavioral skill with more breadth than simply L2-syntax learning. In other words, we propose that the window closing on syntax acquisition in L2 (or, for that matter, any other sub-skill of language acquisition) falls under the closing of a larger biological window of opportunity of some kind.

To better operationalize a ‘critical period,’ Johnson (2011) proposes a framework distinguishing between neurobiological and behavioral views of the critical period. Johnson suggests that, while it may be unreliable to reduce behavior to brain or biological processes, modelling the underlying hardware to a behavior (in this case, L2 syntax learning) could provide insight on the emergence of higher levels of behavior. Johnson further hypothesizes that increased performance in different behavioral domains could be explained by the development of supporting neural “hardware.” HTP rightly point out that “it is hard to say whether any of the identified neural maturational processes might correspond to the changes in syntax acquisition that we observed” (p. 275), so a framework for examining neural changes alongside behavioral performance may be of use in analyzing the developmental trajectory of a skill. In other words, combining neural and behavioral approaches would allow us to connect the development of one to corresponding changes in the other. Using this approach we attempt to elucidate what broader skills may share similar neural and behavioral developments and so underlie the changes in language-specific skills. To this end, we propose the use of two models to connect neural development with behavioral development: Interactive Specialization (IS) ( M. H. Johnson, 2011 ) and Neuroemergentism (NM).

Our argument regarding HTP’s critical period results is that they may not be confined to the narrow domain of L2 syntax learning but represent larger behavioral and neural changes. Therefore, given the power of their study from such a large sample size, their findings may serve as an effective tool for further research into the ways in which behavior and neurobiology organize and reorganize across development. These IS and NM frameworks in concert with the critical period proposed by HTP are likely to shed light on the nature of development. The predictions listed here, based on each framework given HTP’s data, would be instrumental in further testing this critical period. In order to more clearly flesh this argument out, we will review HTP’s findings.

A short summary of HTP’s findings

Hartshorne, Tenenbaum, and Pinker (2018) use a much larger than normal sample (680,333 participants) to investigate the nature of a potential critical period for second language acquisition. HTP argue that a large sample was required in order to make sense of the potential effects that the age of an individual, age of first exposure to L2, and duration of exposure to L2 could have on their results. The use of this approach allowed the authors to arrive at a model that is better able to determine the shape of any decline in L2-learning ability. Analysis puts the onset of this decline at 10-12 years of age, marking the end of the putative “critical period” for L2 learning. Support for this conclusion comes from the small amount of variation in task performance between individuals who began L2 learning in the first decade of life. A sharp decline represents the end of ability in the ‘ultimate’ acquisition of L2 syntax (where abilities could ever reach native-like) beginning around 17.4 years of age. The authors attribute this decline to changes specific to late adolescence, rather than developmental changes that occur in early childhood or during the onset of puberty (for further discussion see Johnson & Newport, 1989 ).

Further support for HTP’s critical period comes from another recent study using online tests to amass an enormous sample size like HTP. In 2015, Hartshorne & Germine found that language task performance (word-pairs in long and short-term memory; word lists) dropped starkly in the late teens. Few other tasks ( i.e. , Reversed Lists, Long-Term Memory for Faces, Arithmetic, Vocabulary knowledge, etc.) had such early drop-offs in performance—most declines seem to occur far later in life. This (and HTP’s complimentary data) contradicts the tendency to focus on early childhood and infancy as the critical periods for language acquisition: developmentally, the experience-dependent ‘word boom’ in early childhood has always represented the peak of language acquisition, and performance afterwards is a trough ( Dale & Fenson, 1996 ; Fenson et al., 1994 ; Weisleder& Fernald, 2013 ). Though, even early-life critical periods of language learning have led to the proposal of a shared mechanism (as do the present proposal and HTP) with other forms of early learning ( Watson et al., 2014 ).

Finally, as an aside, it is worth noting that critical periods in L2 have a more nuanced nature than critical periods in a first language (L1), especially when sequentially acquired (languages not learned simultaneously). Namely, the learning of an L2 builds upon other existing skills that are already present at the time that L2 learning begins ( Newport et al., 2001 ). Any developmental model of language learning must contend with this while also considering the neural processes across the lifespan that may affect (or, more specifically, limit) L2 acquisition.

So far, we have reviewed HTP’s results indicating a steep decline of L2 syntax-learning ability around 17.4 years of age. HTP argue that this finding is compatible with the view that language learning ability is the only ability to show a drop so early in life. We also noted that HTP’s findings may actually be consistent with the view that general cognitive functions may be declining in late adolescence. Recall that this does, however, contrast with the far earlier critical periods for language learning that have been previously discussed in the literature. This raises the need for an explanation of the later-closing critical period; one that takes into account the complications of Unlearning through the lenses of neural development and behavioral development.

Implications of HTP’s findings

In the remaining section of this piece we will consider the implications of HTP’s findings focusing on three specific questions: 1) Why does HTP’s critical period close so much later than those generally used in the language acquisition literature? 2) What role might the decline of other broader cognitive skills play in the decline of L2 learning abilities? 3) What models may best explain the late close of HTP’s critical periods in terms of said other skills? Here, we present two models, Interactive Specialization (IS) and Neuroemergentism (NM) which focus on the relationship between the brain, behavior and development. Taken together these two models may resolve Question 3 and aid in explanations of Questions 1 and 2 using HTP’s data.

The IS framework is centered on the interaction between neighboring brain regions that are specialized to certain tasks leading to behaviors. It proposes a number of clear hypotheses on how this may play out in terms of regional specialization and inter-regional interaction: a) as brain regions specialize, the behaviors associated with activation in said area become more specific and their response to unimportant stimuli diminishes; b) amount of localization for any particular skill can be linked directly to the degree of specialization for that skill; c) a region of the brain with high levels of specialization will be less plastic in the wake of injury than it would if it were less specialized (as it may have been at earlier points in life); d) as cognitive skills develop behaviorally, so too physically do their associated regions; e) as regions specialize and develop, so too do their networks, and vice-versa, leading to smaller, more specialized networks; f) as regions specialize, they are influenced by and so influence their neighbors’ specializations.

IS suggests that behavioral and neural development are a reciprocal process, and over time regions and networks will become more specialized on their own, as networks interconnected within themselves, and in neighborhoods (all reciprocally). This framework has been used to account for language development. For instance, the comparison in brain activity observed before and after the period of extreme vocabulary growth during early childhood revealed language-related activity that was more generalized both in regions of activation and in stimuli to which they would react (see Johnson [2011 , p. 14] for more). Applied to HTP’s critical period data, the IS framework would make a number of predictions.

First, it would predict that activity seen during L2 syntax learning (such as event-related potentials seen in electroencephalograms or cortical blood flow activity changes in functional magnetic resonance imaging scans) would become more specialized over the course of HTP’s critical period (approximately 10-17 years)— i.e., that areas specializing in syntax-learning would show less activity to irrelevant or incorrect stimuli. Second, as key regions further specialize within the behavior, their neighboring regions will retain and refine pertinent abilities and the behavior’s neural networks will shrink. Third, injured neighboring regions’ abilities would not be as readily adopted by other regions in later years of the critical period as in earlier.

Applied to our critical questions, these might offer some solutions. In response to Question 1, the later-closing critical period may be attributed to a longer period of neural development than previously expected: perhaps the hyper-specialization of related regions continues long after heightened plasticity of infancy typically associated with L2 learning ability. To test this, a longitudinal study of language networks and/or activation (fMRI, ERP, etc.), or a cohort-based study of the same regions of interest would help to disambiguate this possibility. In particular, differences before and after early childhood and before and after puberty could be compared and tracked longitudinally. In doing so, we may also be able to answer Question 2 and observe the development of specialized regions (related skills) that were clearly involved in the network in early childhood but pruned out over adolescence and now only tangentially involved. By this method, we may be able to see what skills’ rise and fall could lead to the consequent abilities in L2 learning.

Such a methodology has recently been leveraged by Váša and colleagues in order to understand how the brain changes during adolescence ( Váša et al., 2020 ). To do this they tracked changes in functional connectivity in a group of 14- and 26-year-olds with a focus on cortical and subcortical brain regions over the course of more than 1.5 years. The results of their analyses revealed two different forms of change across development. Some areas showed conservative growth in that they led to stronger connectivity across time whereas others were disruptive in that the interconnectivity changed (either by strengthening or weakening) across development. The areas of the brain represented in these two different types of networks has the potential to shed light on HTP’s data. Areas that were conservative where those involved in sensorimotor processing including but not limited to domains such as movements of body parts and sensory modalities. Areas that showed disruption were associated with higher-level cognition such as memory, theory of mind, and language or sentence processing. Areas that had a disruptive role included those involved in cortical-subcortical communication as well as association areas involved in cortical-cortical processing such as the parietal and prefrontal cortex. Future studies could observe whether the closing of a critical period for syntax does or does not align with the neuroanatomical changes that are occurring during this phase. In a similar vein, studies could also ask participants to complete a number of cognitive, perceptual and motor tasks as well as some second language tasks at different ages. In this way, it would help to see the extent to which second language acquisition might rely on different underlying factors. Using both a behavioral and a neural approach, future studies could investigate the ways in which changes in the ability to learn a second language may shed light on the type of window that is closing during adolescence.

A second framework that may be of use is Neuroemergentism (NM) ( Hernandez et al., 2019 ). NM combines the concepts of a number of different emergentist approaches to neurobehavioral development over the lifespan, including Neuronal Recycling, Neural Reuse and Neuroconstructivism ( Anderson, 2010 ; Dehaene & Cohen, 2007 ; Goldberg, 2006 ; Tomasello, 2009 ; Anderson, 2016 ; Karmiloff-Smith, 2006 ). Essentially, NM provides a developmental framework to account for the specialization of regions and networks in the brain supporting new skills (like language). It considers ontogenetic (individual) development in the discussion of phylogenetic (evolutionary) predispositions of certain regions to certain large-scale skills. These phylogenetically predisposed regions (for instance, the primary auditory cortex) can then be recruited during developmental periods ( i.e. , HTP’s critical period) to perform new functions in a broader ability (like leveraging skills from the auditory systems in language comprehension).

For example, the Visual Word Form Area (VWFA) is specialized for reading and located in the fusiform gyrus across multiple language groups. Although specialized reading had no reason to exist until very recently, reading results in very uniform patterns of neural activity ( Dehaene & Cohen, 2007 ). As was eloquently stated by the authors of the NM framework when discussing Neural Reuse and the VWFA: “The presence of a clearly defined and consistently located VWFA in humans provides evidence this area adapted functions from one set of areas for a very different purpose. The original area was likely involved in more elementary functions such as detecting lines, curves, and intersections. The fact that it was dedicated to such basic functions makes it, according to Anderson (2010) , an ideal circuit for neural reuse and the development of human language and reading. Anderson points out that areas like the VWFA show how the brain can take evolutionarily older areas and reuse them for newer purposes.” ( Hernandez et al., 2019 ).

NM also highlights the idea that no developmental change is isolated to any one region or skill (behavioral or cognitive). This builds on previous work by Elizabeth Bates (1979) who used an emergentist approach to describe the nature of language representation and its neural bases. This can be seen in her classic example of a giraffe which makes use of the same neck bones present in humans. This new neck is not its own new organ, though, nor is its change isolated; the giraffe’s cardiovascular system must adapt to the new height of the head, its back legs must shorten to accommodate the new, higher center of gravity. In the same way, no brain region changes on its own, and to consider it to be singularly responsible for that skill (like a long neck for eating from high trees, or the Fusiform gyrus area for face recognition) would be short-sighted. Should there be an injury (genetic, neural, etc.) to any given skill at some point in its development, that injury would snowball across any number systems, no matter how tangentially involved.

NM complements the approach taken by IS. Both consider the development of specialization: IS via the effect of pruning (localization) of skills to ever-smaller regions and networks, and how those regions affect their neighbors’ specializations; NM via the evolutionary and individual developmental backgrounds of any given ‘old’ system that may be co-opted for ‘new’ skills and the diffuse effects of injury. NM differentiates itself by including the evolutionary background of regions as well as individual changes that occur across the lifespan.

Answers to the questions surrounding HTP’s critical period using the NM framework would be more general than IS. First, it would predict that early-life injury (genetic or neural) to any system involved in syntax learning, no matter how distal, would have an observable effect on the critical period development of that skill. Taken with IS, this could be observed by ERP or fMRI activity over that period when compared to neurodevelopmentally typical L2 learners (Question 1). This could also help elucidate what other cognitive processes are involved in L2 syntax learning through the effect of their injury (again, no matter how tangentially connected) (Question 2). Also, as is illustrated in the original paper, studies on the evolutionary bases of those involved systems may elucidate how they were adapted to L2 syntax learning (also Question 2). Again, these predictions are far more abstract, but this matches the more general framework of NM.

Much discussion of this mysteriously late-closing CP is beyond the scope of this paper, which only seeks to incorporate new frameworks into elucidating its causes. Future research should also consider the age at which this CP would begin, and how that may be modulated by bilingual or monolingual early-life experience. Following this line of thought, research into the difference between early/simultaneous bilinguals and late/sequential bilinguals would also be interesting. IS predicts that during early-life, neighboring regions and networks would be more interactive and interconnected. Thus, an early bilingual could develop and incorporate various skills for use in learning and controlling their languages, while a late bilingual would be limited in their adaptive abilities by the lower plasticity of later life. Research comparing the functional connectivity of highly specialized regions involved in syntax between early and late bilinguals would highlight such incorporation (or exclusion) of other skills or networks. Research of this kind would also address how age of acquisition of L2 influences later-life skills and the differences between monolinguals and bilinguals in HTP’s original work. Understanding how early bilinguals use other skills to improve their language abilities from such a plastic period of life would aid in explaining the differences they show in those skills when later compared to monolinguals and late bilinguals.

These frameworks are neurobiological, and this discussion is meant to encourage linking cognitive and biological approaches, but the effect of environment cannot be ignored when considering critical periods and cognitive development. In fact, inherent in the discussion of genetic predisposition is the need to understand how it interacts with environmental influence. Perhaps such factors as socioeconomic status may have a strong effect on how late a CP like HTP’s closes. Considering how the effects of such factors may differ between early and late bilinguals will also play a role in understanding their influence on the development of skills such as syntax learning.

HTP’s publication involving a large number of participants led to the identification of a critical period for syntax with the window for the acquisition closing at 17.4 years of age. In this piece we describe two frameworks, Interactive Specialization and Neuroemergentism, that could be leveraged in further investigations of HTP’s evidenced critical period and the mechanisms underlying the critical period’s closure. We hope to stimulate future studies that seek to more closely link the closing of this window with neurobiological indices and accompanying psychological processes.

Acknowledgments

The authors confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome . Research reported in this publication was supported by the National Institutes of Health to the National Institute On Aging under Award Number R21AG063537 as well as to the National Institutes of Child Health and Human Development under the Award Number P50HD052117. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

• Anderson ML (2010). Neural reuse: A fundamental organizational principle of the brain . Behavioral and Brain Sciences , 33 ( 4 ), 245–266. 10.1017/S0140525X10000853 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Anderson ML (2016). Neural reuse in the organization and development of the brain . Developmental Medicine & Child Neurology , 58 ( S4 ), 3–6. 10.1111/dmcn.13039 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Bates E (1979). The Emergence of Symbols: Cognition and Communication in Infancy . Academic Press. [ Google Scholar ]
• Dale PS, & Fenson L (1996). Lexical development norms for young children . Behavior Research Methods, Instruments, & Computers , 28 ( 1 ), 125–127. 10.3758/BF03203646 [ CrossRef ] [ Google Scholar ]
• Dehaene S, & Cohen L (2007). Cultural Recycling of Cortical Maps . Neuron , 56 ( 2 ), 384–398. 10.1016/j.neuron.2007.10.004 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Fenson L, Dale PS, Reznick JS, Bates E, Thai DJ, & Pethick SJ (1994). Variability in early communicative development . Monographs of the Society for Research in Child Development , 59 ( 5 ), 1–173; discussion 174–185. [ PubMed ] [ Google Scholar ]
• Goldberg AE (2006). Constructions at Work: The Nature of Generalization in Language . Oxford University Press. [ Google Scholar ]
• Hartshorne JK, & Germine LT (2015). When Does Cognitive Functioning Peak? The Asynchronous Rise and Fall of Different Cognitive Abilities Across the Life Span . Psychological Science , 26 ( 4 ), 433–443. 10.1177/0956797614567339 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Hartshorne JK, Tenenbaum JB, & Pinker S (2018). A critical period for second language acquisition: Evidence from 2/3 million English speakers . Cognition , 177 , 263–277. 10.1016/j.cognition.2018.04.007 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Hernandez AE, Claussenius-Kalman HL, Ronderos J, Castilla-Earls AP, Sun L, Weiss SD, & Young DR (2019). Neuroemergentism: A framework for studying cognition and the brain . Journal of Neurolinguistics , 49 , 214–223. 10.1016/j.jneuroling.2017.12.010 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Johnson JS, & Newport EL (1989). Critical period effects in second language learning: The influence of maturational state on the acquisition of English as a second language . Cognitive Psychology , 21 ( 1 ), 60–99. 10.1016/0010-0285(89)90003-0 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Johnson MH (2011). Interactive Specialization: A domain-general framework for human functional brain development? Developmental Cognitive Neuroscience , 1 ( 1 ), 7–21. 10.1016/j.dcn.2010.07.003 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Karmiloff-Smith A (2006). The tortuous route from genes to behavior: A neuroconstructivist approach . Cognitive, Affective and Behavioral Neuroscience , 6 ( 1 ), 9–17. Scopus 10.3758/CABN.6.1.9 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Newport EL, Bavelier D, & Neville HJ (2001). Critical thinking about critical periods: Perspectives on a critical period for language acquisition . In Language, brain and cognitive development: Essays in honor of Jacques Mehler (pp. 481–502). The MIT Press. [ Google Scholar ]
• Tomasello M (2009). Constructing a Language . Harvard University Press. [ Google Scholar ]
• Váša F, Romero-Garcia R, Kitzbichler MG, Seidlitz J, Whitaker KJ, Vaghi MM, Kundu P, Patel AX, Fonagy P, Dolan RJ, Jones PB, Goodyer IM, the NSPN Consortium, Vértes PE, & Bullmore ET. (2020). Conservative and disruptive modes of adolescent change in human brain functional connectivity . Proceedings of the National Academy of Sciences , 117 ( 6 ), 3248–3253. 10.1073/pnas.1906144117 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Watson TL, Robbins RA, & Best CT (2014). Infant perceptual development for faces and spoken words: An integrated approach: Development of Face and Spoken Language Recognition . Developmental Psychobiology , 56 ( 1 ), 1454–1481. 10.1002/dev.21243 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Weisleder A, & Fernald A (2013). Talking to Children Matters: Early Language Experience Strengthens Processing and Builds Vocabulary . Psychological Science . 10.1177/0956797613488145 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]

Breadcrumbs Section. Click here to navigate to respective pages.

Second Language Acquisition and the Critical Period Hypothesis

DOI link for Second Language Acquisition and the Critical Period Hypothesis

Get Citation

Second Language Acquisition and the Critical Period Hypothesis is the only book on the market to provide a diverse collection of perspectives, from experienced researchers, on the role of the Critical Period Hypothesis in second language acquisition. It is widely believed that age effects in both first and second language acquisition are developmental in nature, with native levels of attainment in both to be though possible only if learning began before the closure of a "window of opportunity" – a critical or sensitive period. These seven chapters explore this idea at length, with each contribution acting as an authoritative look at various domains of inquiry in second language acquisition, including syntax, morphology, phonetics/phonology, Universal Grammar, and neurofunctional factors. By presenting readers with an evenly-balanced take on the topic with viewpoints both for and against the Critical Period Hypothesis, this book is the ideal guide to understanding this critical body of research in SLA, for students and researchers in Applied Linguistics and Second Language Acquisition.

TABLE OF CONTENTS

Chapter 1 | 22  pages, david birdsong, chapter 2 | 16  pages, christine m.weber-fox and helen j.neville, chapter 3 | 26  pages, co-evolution of language size and the critical period, chapter 4 | 36  pages, lynn eubank and kevin r.gregg, chapter 5 | 32  pages, age of learning and second language speech, chapter 6 | 28  pages, theo bongaerts, chapter 7 | 22  pages, ellen bialystok and kenji hakuta.

• Privacy Policy
• Terms & Conditions
• Cookie Policy
• Taylor & Francis Online
• Taylor & Francis Group
• Students/Researchers
• Librarians/Institutions

Connect with us

Registered in England & Wales No. 3099067 5 Howick Place | London | SW1P 1WG © 2024 Informa UK Limited

ORIGINAL RESEARCH article

Critical period in second language acquisition: the age-attainment geometry.

• Teachers College, Columbia University, New York City, NY, United States

One of the most fascinating, consequential, and far-reaching debates that have occurred in second language acquisition research concerns the Critical Period Hypothesis [ 1 ]. Although the hypothesis is generally accepted for first language acquisition, it has been hotly debated on theoretical, methodological, and practical grounds for second language acquisition, fueling studies reporting contradictory findings and setting off competing explanations. The central questions are: Are the observed age effects in ultimate attainment confined to a bounded period, and if they are, are they biologically determined or maturationally constrained? In this article, we take a sui generis , interdisciplinary approach that leverages our understanding of second language acquisition and of physics laws of energy conservation and angular momentum conservation, mathematically deriving the age-attainment geometry. The theoretical lens, termed Energy Conservation Theory for Second Language Acquisition, provides a macroscopic perspective on the second language learning trajectory across the human lifespan.

Introduction

The Critical Period Hypothesis (CPH), as proposed by [ 1 ], that nativelike proficiency is only attainable within a finite period, extending from early infancy to puberty, has generally been accepted in language development research, but more so for first language acquisition (L1A) than for second language acquisition (L2A).

In the context of L2A, there are two parallel facts that appear to compound the difficulty of establishing the validity of CPH. One is that there is a stark difference in the level of ultimate attainment between child and adult learners. “Children eventually reach a more native-like level of proficiency than learners who start learning a second language as adults” ([ 2 ], p . 360). But this fact exists alongside another fact, namely, that there are vast differences in ultimate attainment among older learners. [ 3 ] observed:

Although few adults, if any, are completely successful, and many fail miserably, there are many who achieve very high levels of proficiency, given enough time, input, and effort, and given the right attitude, motivation, and learning environment. ( p . 13).

The dual facets of inter-learner differential success are at the nexus of second language acquisition research. As [ 4 ] once noted:

One of the enduring and fascinating problems confronting researchers of second language acquisition is whether adults can ever acquire native-like competence in a second language, or whether this is an accomplishment reserved for children who start learning at a relatively early age. As a secondary issue, there is the question of whether those rare cases of native-like success reported amongst adult learners are indeed what they seem, and if they are, how it is that such people can be successful when the vast majority are palpably not. ( p . 219).

The primary question Kellerman raised here is, in essence, a critical period (CP) question, concerning differential attainment between child and adult learners, and his secondary question relates to differential attainment among adult learners.

As of this writing, neither question has been settled. Instead, the two phenomena are often seen conflated in debates, including taking evidence for one as counter-evidence for the other (see, e.g., [ 5 ]). By and large, it would seem that the debate has come down to a matter of interpretation; the same facts are interpreted differently as evidence for or against CPH (see, e.g., [ 5 – 7 ]). This state of affairs, tinted with ideological differences over the role of nature and/or nature in language development, continues to put a tangible understanding of either phenomenon out of reach, let alone a coherent understanding of both phenomena. In order to break out of the rut of ‘he said, she said,” we need to engage in systems thinking.

Our research sought to juxtapose child and adult learners, as some researchers have, conceptually, attempted (see, e.g., [ 8 – 11 ]). Specifically, we built on and extended an interdisciplinary model of L2A, Energy Conservation Theory for L2A (ECT-L2A) [ 12 , 13 ], originally developed to account for differential attainment among adult learners, to child learners. In so doing, we sought to gain a coherent understanding of the dual facets of inter-learner differential success in L2A, in addition to mathematically obtaining the geometry of the age-attainment function, a core concern of the CPH/L2A debate.

In what follows, we first provide a quick overview of the CPH research in L2A. We then introduce ECT-L2A. Next, we extend ECT-L2A to the age issue, mathematically deriving the age-attainment function. After that, we discuss the resultant geometry and the fundamental nature of CPH/L2A, and, more broadly, L2 attainment across the human lifespan. We conclude by suggesting a number of avenues for furthering the research on CPH within the framework of ECT-L2A.

However, before we proceed, it is necessary to note two “boundary conditions” we have set for our work. First, the linguistic domain in which we theorize inter-learner differential attainment concerns only the grammatical/computational aspects of language, or what [ 14 , 15 ] calls basic language cognition, which concerns aspects of language where native speakers show little variance. As [ 2 ] has aptly pointed out, much of the confusion in the CPH-L2A debate is attributable to a lack of agreement on the scope of linguistic areas affected by CP. Second, we are only concerned with naturalistic acquisition (i.e., acquisition happens in an input-rich or immersion environment), not instructed learning (i.e., an input-poor environment). These two assumptions are often absent in CPH/L2A research, leading to the different circumstances under which researchers interpret the CP notion and empirical results (for discussion, see [ 7 ]).

The critical period hypothesis in L2A

To date, two questions have dominated the research and debate on CPH/L2A: What counts as evidence of a critical period? What accounts for the age-attainment difference between younger learners and older learners? More than 4 decades of research on CPH/L2A- from [ 16 ] to [ 17 ] to [ 18 ]—have, in the main, found an inverse correlation between the age of acquisition (AoA) and the level of grammatical attainment (see also [ 19 ], for a meta-analysis); “the age of acquisition is strongly negatively correlated with ultimate second language proficiency for grammar as well as for pronunciation” ([ 20 ], p . 88).

However, views are almost orthogonal over whether the observed inverse correlation can count as evidence of CPH or the observed difference is attributable to brain maturation (see, e.g., [ 5 , 7 , 21 – 35 ]).

For some researchers, true evidence or falsification of CPH for L2A must be tied to whether or not late learners can attain a native-like level of proficiency (e.g., [ 36 ]). Others contend that the nativelikeness threshold, in spite of it being “the most central aspect of the CPH” ([ 2 ], p . 362), is problematic, arguing that monolingual-like native attainment is simply impossible for L2 learners [ 37 , 38 ]. Echoing this view, [ 39 ] offered:

[Sequential] bilinguals are not “two monolinguals in one” in any social, psycholinguistic, or cognitive neurofunctional sense. From this perspective, it is of questionable methodological value to quantify bilinguals’ linguistic attainment as a proportion of monolinguals’ attainment, with those bilinguals reaching 100% levels of attainment considered nativelike. ( p . 121).

In the meantime, empirical research into adult learners have consistently produced evidence of selective nativelike attainment, that is, nativelikeness is attained vis-à-vis some aspects of the target language but not others. These studies employed a variety of methodologies, including cross-sectional studies and longitudinal case studies (see, e.g., [ 40 – 56 ]). Some researchers (e.g., [ 55 , 57 ]) take the selective nativelikeness as falsifying evidence of CPH/L2A; other researchers disagree (see, e.g., [ 36 ]).

Leaving aside the vexed issue of nativelikeness, 1 Birdsong [ 58 ], among others, postulated that CPH/L2A must ultimately pass geometric tests: if studies comparing younger learners and older learners yield the geometry of a “stretched Z” for the age-attainment function, that would prove the validity of CPH/L2A, or falsify it, if otherwise. The stretched Z or inverted S [ 20 ] references a bounded period in which the organism exhibits heightened neural plasticity and sensitivity to linguistic stimuli from the environment. This period has certain temporal and geometric features. Temporally, it extends from early infancy to puberty, coinciding with the time during which the brain undergoes maturation [ 1 , 36 , 59 – 62 ]. Geometrically, this period should exhibit two points of inflection or discontinuities, viz, “an abrupt onset or increase of sensitivity, a plateau of peak sensitivity, followed by a gradual offset or decline, with subsequent flattening of the degree of sensitivity” ([ 58 ], p . 111).

By the temporal and geometric hallmarks, few studies seem to have confirmed CPH/L2A, not even those that have allegedly found stark evidence. A case in point is the [ 17 ] study, which reported what appears to be clear-cut evidence of CPH/L2A: r = −.87, p <.01 for the early age of arrival (AoA) group and r = −.16, p >.05 for the late AoA group. As Johnson and Newport described it, “test performance was linearly related to [AoA] up to puberty; after puberty, performance was low but highly variable and unrelated to [AoA],” which supports “the conclusion that a critical period for language acquisition extends its effects to second language acquisition” ( p . 60). However, this claim has been contested.

Focusing on the geometry of the results, [ 58 ] pointed out that the random distribution of test scores within the late AoA group “does not license the conclusion that “through adulthood the function is low and flat” or the corresponding interpretation that “the shape of the function thus supports the claim that the effects of age of acquisition are effects of the maturational state of the learner” ([ 17 ], p . 79)” ( p . 117). Birdsong argued that if CPH holds for L2A, the performance scores of the late AoA group should be distributed horizontally in addition to showing marginal correlation with age. Accordingly, the random distribution of scores could only be taken as indicative of “a lack of systematic relationship between the performance and the AoA and not of a “levelling off of ultimate performance among those exposed to the language after puberty” ([ 17 ], p . 79)” ([ 58 ], p . 118).

Interpreting the same study, other researchers such as [ 20 ] did not set their sights as much on the random distribution of the performance scores among the late learners as on the discontinuity between the early AoA and late AoA groups, arguing that the qualitative difference is sufficient evidence of CPH/L2A.

If geometric satisfaction is one flash point in CPH/L2A research, explaining random distribution of performance scores or, essentially, differential attainment among late learners counts as another. Analyses of late learners’ ultimate attainment (e.g., [ 10 , 22 , 26 , 43 , 63 – 67 ]) have yielded a host of cognitive, socio-psychological, or experiential factors that can be associated with inter-learner differential attainment among late learners. The question, then, is whether or not these non-age factors confound, or even interact with, the age or maturational effect (see discussion in [ 2 , 68 – 72 ]. As Newport [ 7 ] aptly asked, “why cannot other variables interact with age effects?” ( p . 929).

These are undoubtedly complex questions for which sophisticated solutions are needed—beyond the methodological repairs many have thought are solely needed in advancing CPH/L2A research (see, e.g., [ 19 , 67 ]). In the remainder of this article, we take a different tack to the age issue, adopting a theoretical, hybrid approach, ECT-L2A [ 12 , 13 ], to mathematically derive the age-attainment function.

Energy-Conservation Theory for L2A

ECT-L2A is a theoretical model originally developed to account for the divergent states of ultimate attainment in adult L2A [ 12 , 13 ]. Drawing on the physics laws of energy conservation and angular momentum conservation, it theorizes the dynamic transformation and conservation of internal energies (i.e., from the learner) and external energies (i.e., from the environment) in rendering the learner’s ultimate attainment. This model, thus, takes into account nature and nurture factors, and specifically, uses five parameters - the linguistic environment or input, learner motivation, learner aptitude, distance between the L1 and the target language (TL) and the developing learner—and their interaction to account for levels of L2 ultimate attainment.

ECT-L2A draws a number of parallels between mechanical energies and human learning energies: kinetic energy for motivation and aptitude energy, potential energy for environmental energy, 2 and centrifugal energy for L1-TL deviation energy (for discussion, see [ 12 ]). These energies each perform a unique yet dynamic role. As the learner progresses in the developmental process, the energies shift in their dominance, while the total energy remains constant.

Mathematically, ECT-L2A reads as follows:

where ζ r denotes the learner’s motivational energy, r the learner’s position in the learning process relative to the TL, η the distance between L1 and TL, and ρ the input of TL. According to Eq. 1 , the total learning energy, ∈ , comes from the sum of motivation energy ζ r , aptitude (a constant) Λ , deviation energy η 2 r 2 , and environmental energy - ρ r .

The energy types included in Eq. 1 are embodiments of nature and nurture contributions. The potential energy or TL traction, - ρ r , represents the external or environmental energy, while the kinetic or motivational energy, ζ r , along with aptitude, Λ , and the centrifugal or deviation energy η 2 r 2 represent the internal energies.

Under the overarching condition of the total energy being the same or conserved throughout the learning process, ϵ = constant , each type of energy performs a different role, with one converting to another over time as the position of the learner changes in the developmental process.

For mathematical and conceptual convenience, (1) is rewritten into (2) which contains the effective potential energy, U eff (r) .

where U e f f r = η 2 r 2 − ρ r . In other words, the effective potential energy is the sum of deviation energy and the potential energy (see further breakdown in the next section).

The L2A energy system as depicted here is true of every learner, meaning that the total energy is constant for a single learner. But the total energy varies from learner to learner. Accordingly, different learners may reach different levels of ultimate attainment (i.e., closer or more distant from the TL), r 0 . This is illustrated in Figure 1 , where r 0 and r 0 ′ represent the ultimate attainments for learners with different amounts of total energy, ϵ >0 or ϵ <0.

FIGURE 1 . Inter-learner differential ultimate attainment as a function of different amounts of total energy: ϵ >0; ϵ < 0; ϵ = ϵ min [ 12 , 13 ].

Key to understanding Figure 1 is that it is the individual’s total energy that determines their level of attainment. Of the three scenarios on display here, ECT-L2A is only concerned with the case of ϵ ≥0, which represents the unbound process (r 0 , ∞), ignoring the bounded processes of ϵ < 0; ε = ϵmin.

The central thesis of ECT-L2A, as expressed in Eq. 1 , is that the moment a learner begins to receive substantive exposure to the TL, s/he enters a ‘gravitational’ field or a developmental ecosystem in which s/he is initially driven by kinetic or motivational energy, increasingly subject to the traction of the potential or environmental energy, but eventually stonewalled by the deviation energy or centrifugal barrier, resulting in an asymptotic endstate. This trajectory is further elaborated below.

The developmental trajectory depicted and forecast by ECT-L2A

The L2A trajectory begins with the learner at the outset of the learning process or at infinity (r = ∞). Initially, their progression toward the central source, i.e., the TL, is driven almost entirely by their motivation energy and aptitude, as expressed in Eq. 3 .

As learning proceeds, but with r still large (i.e., the learner still distant from the target) and the deviation energy much weaker than the environmental energy, η 2 r 2 ≪ ρ r (due to the second power of r ), the motivation energy rises as a result of its “interaction” with the environmental energy− ρ r , in which case the environmental energy transfers to the motivation energy. Mathematically, this is expressed in Eq. 4 .

As learning further progresses, the environmental energy - ρ r becomes dominant before yielding to the deviation energy η 2 r 2 . Eventually, the deviation energy overrides the environmental energy, as expressed in Eq. 1 , repeated below as Eq. 5 for ease of reference.

The deviation energy is so powerful that it draws the learner away from the target and their learning reaches an asymptote, where their motivation energy becomes minimal, ζ ( r 0 ) = 0, as expressed in Eq. 6 .

At this point, all other energies submit to the deviation energy, including the initial motivation energy ζ (∞) and some of the potential or environmental energy. Consequently, further exposure to TL input would not be of substantive help, meaning that it would not move the learner markedly closer to the target.

Figure 2 gives a geometric expression of the L1-TL deviation η, which is akin to the angular momentum of an object moving in a central force field [ 73 – 75 ]. The deviation from the TL, signifying the distance between the L1 and the TL, varies with different L1-TL pairings. For example, the distance index, according to the Automated Similarity Judgment Program Database [ 76 ], is 90.25 for Italian and English but 100.33 for Italian and Chinese.

FIGURE 2 . Geometric description of the deviation parameter η .

Figure 3 illustrates differential ultimate attainment (indicated by r 0 ) as a function of the deviation parameter η. As η increases, the level of attainment is lower or the attainment is further away from the target ( r = 0).

FIGURE 3 . Effective potentials U eff with different values of η [ 12 , 13 ].

For adult L2A, ECT-L2A predicts, inter alia , that high attainment is possible but full attainment is not. In other words, near-nativelike attainment is possible, but complete-nativelike attainment is not. ECT-L2A also predicts that while motivation and aptitude are part and parcel of the total energy of a given L2 learner, their role is largely confined to the earlier stage of development. Most of all, ECT-L2A predicts that the L1-L2 deviation is what keeps L2 attainment at asymptote.

For L2 younger learners, ECT-L2A also makes a number of predictions to which we now turn.

ECT-L2A vis-à-vis younger learners

As highlighted above, the deviation energy is what leads L2 attainment to an asymptote. It follows that as long as η (i.e., the L1-TL distance) is non-zero, the learner’s ultimate attainment, r 0 , will always eventuate in an asymptote. As shown in Figure 3 , the larger the deviation r 0 , the more distant the ultimate attainment r 0 is from the TL. Put differently, a larger η portends that learning would reach an asymptote earlier or that the ultimate attainment would be less native-like. But how does that work for child L2A?

On the ECT-L2A account, it is the low η value that determines child learners’ superior attainment. In child L2 learners, the deviation is low, because of the incipient or underdeveloped L1. However, as the L1 develops, the η value grows until it becomes a constant, presumably happening around puberty 3 , hence coinciding with the offset of the critical period [ 1 ]. As shown in Figures 1 , 3 , the smaller the deviation, η, the closer r 0 (i.e., the ultimate level of attainment) is to the TL or the higher the ultimate attainment.

From Eq. 6 the ultimate attainment of any L2 learner, irrespective of age, can be mathematically derived:

where ε = ϵ – Λ (i.e., total energy minus aptitude). r 0 here again denotes ultimate attainment. The upper panel in Figure 4 displays the geometry of ultimate attainment as a function of deviation, η.

FIGURE 4 . Double non-linearity of r 0 η [ (A) : first non-linearity] and η t [ (B) : second non-linearity] at early AoA.

For a given child learner, η is a constant, but different child learners can have a different η value, depending on their AoA . Herein lies a crucial difference from adult learning where η is a constant for all learners because of their uniform late AoA or age of acquisition and because their L1 has solidified. Adult learning starts at a time when the deviation between their L1 and the TL has become fixed, so to speak, as a result of having mastered their L1 (see the lower panel of Figure 4 ).

Further, for child L2 learners, η is simultaneously a function of their AoA, a proxy for time ( t ), and can therefore be expressed as η(t). This deviation function of time varies in the range of 0 ≤ η t ≤ η max . Accordingly; Eq. 7 can be mathematically rewritten into (8):

Assuming that as t grows or as AoA increases, η increases slowly and smoothly from 0 to η max until it solidifies into a constant, which marks the onset of adult learning, η( t ) can mathematically be expressed as (9).

where a is a constant. The geometry of the deviation function of time is illustrated in the lower panel of Figure 4 .

Figure 4 displays a double non-linearity characterizing L2 acquisition by young learners, with (A) showing the first order of non-linearity of r 0 η , that is, ultimate attainment as a function of deviation or the L1-TL distance (computed via Eq. 7 ), and with (B) displaying the second order of non-linearity, η (t), that is, η changing with t , age of acquisition (computed through Eq. 9 ).

Figure 5 illustrates ultimate attainment as a function of AoA, r 0 (t), and its derivative against t , d r 0 d t , which naturally yields three distinct periods: a critical period, t critical ; a post-critical period, t p-critical ; and an adult learning period, t adult . Within the critical period, t critical , r 0 ≅ 0 , meaning there is no real difference in attainment as age of acquisition increases. But within the post-critical period, t p-critical , r 0 changes dramatically, with d r 0 d t peaking and waning until it drops to the level approximating that of the adult period. Within the adult period, t adult , r 0 remains a constant, as attainment levels off.

FIGURE 5 . Ultimate attainment (the blue line) as a function of age of acquisition ( t ) and its derivatives giving three distinct periods (the orange line).

ECT-L2A, therefore, identifies three learning periods. First, there is a critical period, t critical , within which attainment is nativelike, r 0 ≅ 0. Notice that the blue line in Figure 5 is the lowest during the critical period, signifying that the attainment converges on the target, but it is the highest during the adult period, meaning that the attainment diverges greatly from the target. The offset of the critical period is smooth rather than abrupt, with the impact of deviation, η , slowly emerging at its offset. During this period, the L1 is surfacing, yet with negligible deviation from the TL and weak in strength.

Key to understanding this account of the critical period is the double non-linearity: first, ultimate attainment as a function of L1-TL deviation ( r 0 ( η ), see (A) in Figure 4 ); and second, L1-TL deviation as a function of AoA ( η ( t ); see (B) in Figure 4 ). Crucially, this double non-linearity extends a critical “point” into a critical “period” .

Second, there is a post-critical period, t p-critical , 0 < r 0 ≤ r 0 ( η max ), within which, with advancing AoA, the L1-L2 deviation grows larger and stronger, resulting in ultimate attainment that is increasingly lower (i.e., increasingly non-nativelike). The change rate of r 0 , its first derivative to time, d r 0 d t , is dramatic, waxing and waning. As such, the post-critical period is more complex and nuanced than the critical period. During the post-critical period, as the learner’s L1 becomes increasingly robust and developed, the deviation becomes larger, resulting in a level of attainment increasingly away from the target (i.e., increasingly non-nativelike).

Third, there is an adult learning period, t adult , η = η max ≅ constant, where, despite the continuously advancing AoA, the deviation reaches its maximum and remains a constant, as benchmarked in indexes of crosslinguistic distance (see, e.g., the Automated Similarity Judgment Program Database [ 76 ]). As a result, L2 ultimate attainment turns asymptotic (for discussion, see [ 12 , 13 ]).

The three periods mathematically produced by ECT-L2A coincide with the stretched “Z” slope that some researchers have argued (e.g., [ 17 , 58 , 59 ]) constitutes the most unambiguous evidence for CPH/L2A, and by extension, for a maturationally-based account of the generic success or lack thereof (i.e., nativelike or non-nativelike L2 proficiency) in early versus late starters. For better illustration of the stretched “Z,” we can convert Figure 5 into Figure 6 , using Eq. 10 .

where a t t stands for level of attainment. According to Eq. 10 , the smaller the r 0 is, the higher the attainment is.

FIGURE 6 . Level of attainment as a function of AoA.

In sum, ECT-L2A mathematically establishes the critical period geometry. That said, the geometry, as seen in Figure 6 , exhibits anything but abrupt inflections; the phase transitions are gradual and smooth. The adult period, for example, does not exhibit a complete “flattening” but markedly lower attainment with continuous decline (cf. [ 7 , 23 , 28 ]). 4

Explaining CPH/L2A

As is clear from the above, on the ECT-L2A account of the critical period, η (i.e., L1-TL deviation) is considered an inter-learner variable and, at once, a proxy for age of acquisition, t . More profoundly, however, ECT-L2A associates η with neural plasticity or sensitivity (cf [ 77 ]). The relationship between plasticity, p ( t ), and deviation function, η (t) , is expressed as (11):

Thus, the relationship between plasticity and the deviation function is one of inverse correlation. During the critical period, η = η min (i.e., minimal L1-TL deviation) and p = p max (i.e., maximal plasticity); conversely, during the adult learning period, η = η max (i.e., maximal L1-TL deviation) and p = p min (i.e., minimal plasticity). In short, an increased deviation, η (t) , corresponds to a decrease of plasticity, p (t) , and vice versa , as illustrated in Figure 7 .

FIGURE 7 . Plasticity as a function of age of acquisition.

Illustrated in Figure 7 is that neural plasticity, first proposed by [ 78 ] as the underlying cause of CP, is at its highest during the critical period and, as [ 79 ] put it, it “endures within the confines of its onset and offset” ( p . 182). But it begins to decline and drops to a low level during the post-critical period, and remains low through the adult learning period. 5 It would, therefore, seem reasonable to call the first period “critical” and the second period “sensitive.” It is worth mentioning in passing that the post-critical or sensitive period has thus far received scant empirical attention in CPH/L2A research.

Temporally, following the [ 59 ] conjecture, the critical period should last through early childhood from birth to age six, and the sensitive period should offset around puberty (see also [ 2 , 20 , 36 , 67 , 71 ]). Crucially, both periods are circumscribed, exhibiting discontinuities, with the critical period exhibiting maximal sensitivity, the sensitive period declining, though, for the most part, still far greater, sensitivity than the adult learning period. This view of a changing underlying mechanism across the three periods of AoA and attainment resonates with the Language as a Complex Adaptive System perspective (see, e.g., [ 80 ]). [ 81 ], for example, noted that “the processing mechanisms that underlie [language development] … are fundamentally non-linear. This means that development itself will frequently have phase-like characteristics, that there may be periods of extreme sensitivity to input (‘critical periods’)” ( p . 431).

ECT-L2A as a unifying model

ECT-L2A, by virtue of identifying the L1-TL deviation, η, as a lynchpin for age effects, provides an explanation for the differential ultimate attainment of early versus late starters. Essentially, in early AoA, η is a temporal and neuro-functional proxy tied respectively to a developing L1 and to a changing age and changing neuroplasticity. In contrast, in late AoA, η is a constant, due to the L1 being fully developed and the brain fully mature. This takes care of the first facet of inter-learner differential attainment. What about the second facet, viz., the inter-learner differential attainment among late learners?

ECT-L2A (as expressed in Eq. 1 ) is a model of an ecosystem where there is an interplay between learner-internal and environmental energies. In line with the general finding from L2 research that individual difference variables are largely responsible for inter-learner differential attainment of nativelike proficiency in adult learners (see, e.g., [ 27 , 35 , 77 , 82 , 83 ]), ECT-L2A specifically ties motivation and aptitude to kinetic energy, only to provide a more nuanced picture of the changing magnitude of individual difference variables.

Figure 8 illustrates the twin facets of inter-learner differential attainment. First, attainment varies as a function of AoA. Second, attainment varies within and across the three learning periods as a function of individual learners with different amounts of total energy, ϵ 1 < ϵ 2 < ϵ 3 . As shown, individual differences play out the least among learners of AoA falling within the critical period but the most within the adult learning period, consistent with the general findings from L2 research (see, e.g., [ 2 , 3 , 43 , 63 , 65 , 67 , 84 , 85 ]). During the post-critical or sensitive period, individual differences are initially non-apparent but become more pronounced with increasing AoA. 6

FIGURE 8 . Level of attainment for total energies ϵ 1 < ϵ 2 < ϵ 3 .

ECT-L2A thus offers a coherent explanation for variable attainment in late learners. First and foremost, it posits that individual learners’ total energy or “carrying capacity” [ 86 ] is different, which leads to different levels of attainment. Second, although the internal (motivation and aptitude) and external (environment) energies interact over time, ultimately it is the deviation energy η 2 r 2 that dominates and stalls the learner at asymptote (see Eq. 6 ). This account provides a much more nuanced perspective on the role of individual differences than has been given in the current L2A literature.

Extant empirical studies investigating individual difference variables through correlation analysis have mostly projected a static view of the role (some of) the variables play in L2A. In contrast, ECT-L2A gives a dynamic view and, more importantly, an interactive view. In the end, the individual difference variables are part of a larger ecosystem within which they do not act alone, but rather interact with other energies (i.e., potential energy and deviation energy), waxing and waning as a result of energy conservation.

In this article, we engaged with a central concern in the ongoing heated debate on CPH/L2A, that is, the geometry of age differences. Within the framework of ECT-L2A, an interdisciplinary model of L2 attainment, we mathematically derived the age-attainment function and established the presence of a critical period in L2A. Importantly, this period is part of a developmental trajectory that comprises three learning periods: a critical period, a post-critical or sensitive period, and an adult period.

ECT-L2A has thus far demonstrated a stunning internal consistency in that it mathematically identifies younger learners’ superior performance to adult learners’ as well as the differential attainment among adult learners.

ECT-L2A, while in broad agreement with an entrenchment-transfer account from L2A research that essentializes the role of the L1 in L2 attainment (see, e.g., [ 5 , 11 , 87 – 90 ]), provides a dynamic account of that role and its varying contributions to the different age-related learning periods. Furthermore, ECT-L2A offers an interactive account whereby the L1, as part of the deviation energy, interacts with other types of learner-internal and learner-external energies. Above all, ECT-L2A, by virtue of summoning internal and external energies, gives a coherent explanation for the twin facets of inter-learner differential success—as respectively manifested between younger and older learners and among older learners.

Validation of ECT-L2A is, however, required. Many questions warrant investigation. On this note, Johnson and Newort’s view [ 17 ], in particular, that the goal of any L2A theory should be to account for three sets of facts—a) gradual decline of performance, b) the age at which a decline in performance is detected, and c) the nature of adult performance—resonates with us. Although ECT-L2A shines a light on all three, further work is clearly needed. More specific to the focus of the present article, three sets of questions can be asked in relation to the three learning periods ECT-L2A has identified.

In the spirit of promoting collective intelligence, we present a subset of these questions below in the hope that they will spark interest among researchers across disciplines and inspire close-up investigations leveraging a variety of methodologies.

First, for the critical period:

1. When does the decline of learning begin?

2. How does it relate to the status of L1?

3. What is plasticity like in this period?

4. What does plasticity entail?

5. How is it related to a developing L1 and a developing L2?

Answers to these questions can, at least in part, be found in the various literatures across disciplines. But approaching these questions in relation to one another—as opposed to discretely—would likely yield a more systematic, holistic and coherent understanding. Or perhaps, in search of answers to any of these questions, one may realize that the existing understanding is way too shallow or inadequate. For instance, [ 18 ] cited “a lack of interference from a well-learned first language” as one of the possible causes of the age-attainment function in younger versus older learners. But what has not yet been established is the nature of the younger learners’ L1. What does “well-learned” mean? Is it established or is it still developing? At minimum, it cannot be a unitary phenomenon, given the age span of young learners.

Second, for the post-critical or sensitive period, ECT-L2A mathematically identifies two sub-periods. Thus, questions such as the following should be examined:

6. What prompts the initial dramatic decline of attainment?

7. How does each of the sub-periods relate to the status of L1?

8. How does the decline relate to changing plasticity?

9. How does it relate to grammatical performance?

Third, for the adult learning period, questions such as the following warrant close engagement:

10. How do learners with the same L1 background differ from each other in their L2 ultimate attainment?

11. How do learners with different L1 backgrounds differ from one another in their L2 ultimate attainment?

12. How is the trajectory of each type of energy, endogenous or exogenous, related to the level of attainment?

Investigating these questions, among others, will lead us to a better understanding not only of the critical period but also of L2 learning over the arc of human life.

The theoretical and practical importance of gaining a robust and comprehensive understanding of how age affects the L2 learning outcome calls for systematic investigations. To that end, ECT-L2A has offered a systems thinking perspective and framework.

Data availability statement

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.

Author contributions

All authors listed have made a substantial, direct, and intellectual contribution to the work and approved it for publication.

Acknowledgments

We greatly appreciate the insightful and perceptive comments made by the reviewers on an earlier version of this article, and take sole responsibility for any error or omission.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

1 Despite the centrality of “nativelikeness” to the Critical Period Hypothesis [ 1 ], studies in L2A have increasingly moved away from the use of the term in favor of “the level of ultimate attainment” [ 2 ].

2 The potential energy in ECT-L2A is akin to gravitational potential energy. As such it defines the central source field, serving as the primary energy that dynamically converts to other types of energy: kinetic energy and centrifugal energy. Similarly, the potential energy of L2A defines the field of learning. It stands for TL environment or input, serving as primary energy, dynamically converting to motivational and L1-TL deviation energies. An essential premise of ECT-L2A is the existence of potential energy. This premise is consistent with that underpinning L2A studies on CPH and ultimate attainment.

3 That is when the L1 becomes entrenched.

4 Looking back on the [ 17 ] study, [ 7 ], taking account of developments in the intervening 3 decades in understanding changes in the brain during adulthood, updated the earlier assertation about the stability of age effects in adulthood, noting that “it is more accurate to hypothesize that L2 proficiency SHOULD continue to decline during adulthood” and that “a critical or sensitive period for language acquisition is not absolute or sudden” ( p . 929, emphasis in original). She further argued that “[t]he lack of flattening of age function at adulthood in many studies does not mean that learning is not constrained by biologically based maturational changes” (ibid).

5 The plasticity never completely disappears, but rather becomes asymptotic.

6 Age and attainment function appears to follow a power law in that age effects are greatest during the critical period, less so during the post-critical or sensitive period, and weakest during the adult learning period (see Figure 8 ). Similarly, Figure 7 exhibits a power law relationship between age and plasticity: Plasticity is at its peak during the critical period, declines during the post-critical or sensitive period, and plateaus in the adult learning period.

1. Lenneberg E. Biological foundations of language . Wiley (1967).

Google Scholar

2. Hyltenstam K. Critical period. In: C Chappell, editor. The concise encyclopedia of applied linguistics . John Wiley and Sons (2020). p. 360–4.

CrossRef Full Text | Google Scholar

3. Bley-Vroman R. The logical problem of second language learning. Linguistic Anal (1990) 20(1-2):3–49.

4. Kellerman E (1995). Age before beauty: Johnson and Newport revisited. In L Eubank, L Selinker, and M Sharwood Smith (Eds.), The current state of interlanguage: Studies in honor of William Rutherford , 219–31. John Benjamins .

5. Mayberry RI, Kluender R. Rethinking the critical period for language: New insights into an old question from American Sign Language. Bilingualism: Lang Cogn (2018) 21(5):938–44. doi:10.1017/s1366728918000585

6. Abrahamsson N. But first, let’s think again. Bilingualism: Lang Cogn (2018) 21(5):906–7. doi:10.1017/s1366728918000251

7. Newport E (2018). Is there a critical period for L1 but not L2? Bilingualism: Lang Cogn 21(5), 928–9. doi:10.1017/s1366728918000305

8. Foster-Cohen S. First language acquisition.second language acquisition: What's Hecuba to him or he to Hecuba? Second Lang Res (2001) 17:329–44. doi:10.1191/026765801681495859

9. Herschensohn J. Language development and age . Cambridge University Press (2007).

10. Meisel J. Sensitive phases in successive language acquisition: The critical period hypothesis revisited. In: C Boeckx, and K Grohmann, editors. The Cambridge handbook of biolinguistics . Cambridge University Press (2013). p. 69–85.

11. MacWhinney B. A unified model. In: P Robinson, and N Ellis, editors. Handbook of cognitive linguistics and second language acquisition . Cambridge University Press (2008). p. 229–52.

12. Han Z-H, Bao G, Wiita P. Energy conservation: A theory of L2 ultimate attainment. Int Rev Appl Linguistics (2017) 50(2):133–64. doi:10.1515/iral-2016-0034

13. Han Z-H, Bao G, Wiita P. Energy conservation in SLA: The simplicity of a complex adaptive system. In: L Ortega, and Z-H Han, editors. Complexity theory and language development. In celebration of Diane Larsen-Freeman . John Benjamins (2017). p. 210–31.

14. Hulstijn JH. Language proficiency in native and non-native speakers: Theory and research . John Benjamins (2015).

15. Hulstijn JH. An individual-differences framework for comparing nonnative with native speakers: Perspectives from BLC Theory. Lang Learn (2019) 69:157–83. doi:10.1111/lang.12317

16. Oyama S. A sensitive period for the acquisition of a non-native phonological system. J Psycholinguistic Res (1976) 5:261–83. doi:10.1007/bf01067377

17. Johnson JS, Newport EL. Critical period effects in second language learning: The influence of maturational state on the acquisition of English as a second language. Cogn Psychol (1989) 21(1):60–99. doi:10.1016/0010-0285(89)90003-0

PubMed Abstract | CrossRef Full Text | Google Scholar

18. Hartshorne JK, Tenenbaum JB, Pinker S. A critical period for second language acquisition: Evidence from 2/3 million English speakers. Cognition (2018) 177:263–77. doi:10.1016/j.cognition.2018.04.007

19. Qureshi M. A meta-analysis: Age and second language grammar acquisition. System (2016) 60:147–60. doi:10.1016/j.system.2016.06.001

20. DeKeyser R, Larson-Hall J. What does the critical period really mean? In: J Kroll, and AMB de Groot, editors. Handbook of bilingualism: Psycholinguistic approaches . Oxford University Press (2005). p. 88–108.

21. Abutalebi J, Clahsen H. Critical periods for language acquisition: New insights with particular reference to bilingualism research. Bilingualism: Lang Cogn (2018) 21(5):883–5. doi:10.1017/s1366728918001025

22. Bialystok E, Hakuta K. Confounded age: Linguistic and cognitive factors in age differences for second language acquisition. In: D Birdsong, editor. Second language acquisition and the Critical Period hypothesis . Lawrence Erlbaum (1999). p. 161–82.

23. Bialystok E, Miller B. The problem of age in second language acquisition: Influences from language, structure, and task. Bilingualism: Lang Cogn (1999) 2:127–45. doi:10.1017/s1366728999000231

24. DeKeyser R. Age effects in second language learning. In: S Gass, and A Mackey, editors. The Routledge handbook of second language acquisition . Routledge (2012). p. 422–60.

25. Hakuta K, Bialystok E, Wiley E. Critical evidence: A test of the critical-Period Hypothesis for second-language acquisition. Psychol Sci (2013) 14(1):31–8. doi:10.1111/1467-9280.01415

26. Birdsong D. Age and second language acquisition and processing: A selective overview. Lang Learn (2006) 56:9–49. doi:10.1111/j.1467-9922.2006.00353.x

27. Birdsong D. Plasticity, variability, and age in second language acquisition and bilingualism. Front Psychoogy (2018) 9(81):81–17. doi:10.3389/fpsyg.2018.00081

28. Birdsong D, Molis M. On the evidence for maturational constraints in second language acquisition. J Mem Lang (2001) 44:235–49. doi:10.1006/jmla.2000.2750

29. Long M. Problems with supposed counter-evidence to the critical period hypothesis. Int Rev Appl Linguistics Lang Teach (2005) 43:287–317. doi:10.1515/iral.2005.43.4.287

30. Long MH. Problems in SLA . Lawrence Erlbaum Associates (2007).

31. Long MH. Maturational constraints on child and adult SLA. In: G Granena, and MH Long, editors. Sensitive periods, language aptitude, and ultimate L2 attainment . John Benjamins (2013). p. 3–41.

32. Mayberry RI, Lock E. Age constraints on first versus second language acquisition: Evidence for linguistic plasticity and epigenesis. Brain Lang (2003) 87(3):369–84. doi:10.1016/s0093-934x(03)00137-8

33. Marinova-Todd S, Marshall DB, Snow CE. Three misconceptions about age and L2 learning. TESOL Q (2000) 34:9–34. doi:10.2307/3588095

34. Muñoz C, Singleton D. A critical review of age-related research on L2 ultimate attainment. Lang Teach (2010) 44(1):1–35. doi:10.1017/s0261444810000327

35. Singleton D. Age and second language acquisition. Annu Rev Appl Linguistics (2001) 21:77–89. doi:10.1017/s0267190501000058

36. Long M. Maturational constraints on language development. Stud Second Lang Acquisition (1990) 12:251–85. doi:10.1017/s0272263100009165

37. Cook V. Evidence for multi-competence. Lang Learn (1992) 42:557–91. doi:10.1111/j.1467-1770.1992.tb01044.x

38. Grosjean F. Studying bilinguals: Methodological and conceptual issues. Bilingualism: Lang Cogn (1989) 1:131–49. doi:10.1017/s136672899800025x

39. Birdsong D. Nativelikeness and non-nativelikeness in L2A research. Int Rev Appl Linguistics (2005) 43(4):319–28. doi:10.1515/iral.2005.43.4.319

40. Birdsong D. Ultimate attainment in second language acquisition. Language (1992) 68(4):706–55. doi:10.2307/416851

41. Coppieters R. Competence differences between native and near-native speakers. Language (1987) 63:544–73. doi:10.2307/415005

42. Donaldson B. Left-dislocation in near-native French. Stud Second Lang Acquisition (2011) 33:399–432. doi:10.1017/s0272263111000039

43. Donaldson B. Syntax and discourse in near-native French: Clefts and focus. Lang Learn (2012) 62(3):902–30. doi:10.1111/j.1467-9922.2012.00701.x

44. Franceschina F. Fossilized second language grammars: The acquisition of grammatical gender (Vol. 38) . John Benjamins (2005).

45. Han Z-H. Fossilization: Can grammaticality judgment be a reliable source of evidence? In: Z-H Han, and T 672 Odlin, editors. Studies of fossilization in second language acquisition . Multilingual Matters (2006). p. 56–82.

46. Han Z-H. Grammatical morpheme inadequacy as a function of linguistic relativity: A longitudinal study. In: ZH Han, and T Cadierno, editors. Linguistic relativity in SLA: Thinking for speaking . Clevedon: Multilingual Matters (2010). p. 154–82.

47. Hopp H. Ultimate attainment in L2 inflection: Performance similarities between non-native and native speakers. Lingua (2010) 120:901–31. doi:10.1016/j.lingua.2009.06.004

48. Hopp H. Grammatical gender in adult L2 acquisition: Relations between lexical and syntactic variability. Second Lang Res (2013) 29(1):33–56. doi:10.1177/0267658312461803

49. Ioup G, Boutstagui E, El Tigi M, Moselle M. Re-Examining the critical period hypothesis: A case study of successful adult sla in a naturalistic environment. Stud Second Lang Acquisition (1994) 10:73–98. doi:10.1017/s0272263100012596

50. Lardiere D. Ultimate attainment in second language acquisition . Lawrence Erlbaum (2007).

51. Saito K. Experience effects on the development of late second language learners' oral proficiency. Lang Learn (2015) 65(3):563–95. doi:10.1111/lang.12120

52. Sorace A. Unaccusativity and auxiliary choice in non-native grammars of Italian and French: Asymmetries and predictable indeterminacy. J French Lang Stud (1993) 3:71–93. doi:10.1017/s0959269500000351

53. Stam G. Changes in thinking for speaking: A longitudinal case study. In: E Bylund, and P Athanasopolous, Guest editors. The language and thought of motion in second language speakers . The modern language journal , 99 (2015). p. 83–99.

54. van Baxtel S. Can the late bird catch the worm? Ultimate attainment in L2 syntax . Landelijke Onderzoekschool Taalwetenschap (2005).

55. White L, Genesee F. How native is near-native? The issue of ultimate acquisition. Second Lang Res (1996) 12(3):233–65. doi:10.1177/026765839601200301

56. Yuan B, Dugarova E. Wh-topicalization at the syntax-discourse interface in English speakers' L2 Chinese grammars. Stud Second Lang Acquisition (2012) 34:533–60. doi:10.1017/s0272263112000332

57. Birdsong D. Introduction: Why and why nots of the critical period hypothesis. In: D Birdsong, editor. Second language acquisition and the critical period hypothesis . Erlbaum (1999). p. 1–22.

58. Birdsong D. Interpreting age effects in second language acquisition. In: J Kroll, and A De Groot, editors. Handbook of bilingualism: Psycholinguistic approaches . Oxford University Press (2005). p. 109–27.

59. Pinker S. The language instinct . W. Morrow (1994).

60. Pulvermüller F, Schumann J. Neurobiological mechanisms of language acquisition. Lang Learn (1994) 44:681–734. doi:10.1111/j.1467-1770.1994.tb00635.x

61. Scovel T. A time to speak: A psycholinguistic inquiry into the critical period for human speech . Newbury House (1988).

62. Scovel T. A critical review of the critical period research. Annu Rev Appl Linguistic (2000) 20:213–23. doi:10.1017/s0267190500200135

63. Abrahamsson N, Hyltenstam K. The robustness of aptitude effects in near-native second language acquisition. Stud Second Lang Acquisition (2008) 30:481–509. doi:10.1017/s027226310808073x

64. Bialystok E, Kroll J. Can the critical period be saved? A bilingual perspective. Bilingualism: Lang Cogn (2018) 21(5):908–10. doi:10.1017/s1366728918000202

65. DeKeyser R. The robustness of critical period effects in second language acquisition. Stud Second Lang Acquisition (2000) 22(4):499–533. doi:10.1017/s0272263100004022

66. Flege J, Yeni-Komshian G, Liu S. Age constraints on second-language acquisition. J Mem Lang (1999) 41:78–104. doi:10.1006/jmla.1999.2638

67. Granena G, Long MH. Age of onset, length of residence, language aptitude, and ultimate L2 attainment in three linguistic domains. Second Lang Res (2013) 29(3):311–43. doi:10.1177/0267658312461497

68. Birdsong D, Vanhove J. Age of second-language acquisition: Critical periods and social concerns. In: E Nicoladis, and S Montanari, editors. Bilingualism across the lifespan: Factors moderating language proficiency . Washington, DC: American Psychological Association (2016). p. 162–81.

69. Flege JE. It’s input that matters most, not age. Bilingualism: Lang Cogn (2018) 21:919–20. doi:10.1017/s136672891800010x

70. Hyltenstam K. Second language ultimate attainment: Effects of maturation, exercise, and social/psychological factors. Bilingualism: Lang Cogn (2018) 21(5):921–3. doi:10.1017/s1366728918000172

71. Hyltenstam K, Abrahamsson N. Maturational constraints in SLA. In: C Doughty, and M Long, editors. The handbook of second language acquisition . Blackwell (2003). p. 539–88.

72. Long M, Granena G. Sensitive periods and language aptitude in second language acquisition. Biling: Lang Cogn (2018) 21(5):926–927.

73. Bao G, Hadrava P, Ostgaard E. Multiple images and light curves of an emitting source on a relativistic eccentric orbit around a black hole. Astrophysics J (1994) 425:63–71. doi:10.1086/173963

74. Bao G, Hadrava P, Ostgaard E. Emission line profiles from a relativistic accretion disk and the role of its multi-images. Astrophysics J (1994) 435:55–65.

75. Bao G, Wiita P, Hadrava P. Energy-dependent polarization variability as a black hole signature. Phys Rev Lett (1996) 77:12–5. doi:10.1103/PhysRevLett.77.12

76. Wichmann S, Holman E, Brown C. The ASJP database (version 17) (2016). Available at http://asjp.clld.org (Accessed November 1, 2020).

77. MacWhinney B. Emergent fossilization. In: Z-H Han, and T Odlin, editors. Studies of fossilization in second language acquisition . Multilingual Matters (2006). p. 134–56.

78. Penfield W, Roberts L. Speech and brain mechanisms . Atheneum (1959).

79. Bornstein MH. Sensitive periods in development: Structural characteristics and causal interpretations. Psychol Bull (1989) 105:179–97. doi:10.1037/0033-2909.105.2.179

80. Larsen-Freeman L. Complex dynamic systems theory. In: B VanPatten, G Keating, and S Wulff, editors. Theories in second language acquisition . Routledge (2020). p. 248–70.

81. Elman J. Development: It’s about time. Dev Sci (2003) 6:430–3. doi:10.1111/1467-7687.00297

82. Dörnyei Z, Skehan P. Individual differences in second language learning. In: C Doughty, and M Long, editors. The handbook of second language acquisition . Blackwell (2003). p. 589–630.

83. Hyltenstam K, Abrahamsson N. Who can become native-like in a second language? All, some, or none? Studia Linguistica (2000) 54(2):150–66. doi:10.1111/1467-9582.00056

84. Reber A. Implicit learning and tacit knowledge: An essay on the cognitive unconscious . Clarendon Press (1993).

85. Hoyer W, Lincourt A. Ageing and the development of learning. In: M Stadler, and P Frensch, editors. Handbook of implicit learning . Sage (1998). p. 445–70.

86. van Geert P. A dynamic systems model of cognitive and language growth. Psychol Rev (1991) 98:3–53. doi:10.1037/0033-295x.98.1.3

87. Elman J, Bates E, Johnson M, Karmiloff-Smith A, Parisi D, Plunkett K. Rethinking innateness: A connectionist perspective on development . Cambridge, MA: MIT Press (1996).

88. Flege J. Age of learning and second language speech. In: D Birdsong, editor. Second language acquisition and the Critical Period hypothesis . Lawrence Erlbaum (1999).

89. Schepens J, Roeland W, van Hout F, van der Slik F. Linguistic dissimilarity increases age-related decline in adult language learning. Stud Second Lang Acquisition (2022) 1–22. doi:10.1017/S0272263122000067

90. Ventureyra V, Pallier C, Yoo H. The loss of first language phonetic perception in adopted Koreans. J Neurolinguist (2004) 17:79–91. doi:10.1016/s0911-6044(03)00053-8

Keywords: ultimate attainment, critical period, second language acquisition, physics laws, energy conservation, angular momentum conservation, inter-learner differential attainment

Citation: Han Z and Bao G (2023) Critical period in second language acquisition: The age-attainment geometry. Front. Phys. 11:1142584. doi: 10.3389/fphy.2023.1142584

Received: 11 January 2023; Accepted: 02 March 2023; Published: 20 March 2023.

Reviewed by:

Copyright © 2023 Han and Bao. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: ZhaoHong Han, [email protected]

Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

The Critical Period Hypothesis for Second Language Acquisition: Tailoring the Coat of Many Colors

• First Online: 01 January 2013

Cite this chapter

• David Birdsong 4  

Part of the book series: Second Language Learning and Teaching ((SLLT))

3188 Accesses

16 Citations

The present contribution represents an extension of David Singleton’s ( 2005 ) IRAL chapter, “The Critical Period Hypothesis: A coat of many colours”. I suggest that the CPH in its application to L2 acquisition could benefit from methodological and theoretical tailoring with respect to: the shape of the function that relates age of acquisition to proficiency, the use of nativelikeness for falsification of the CPH, and the framing of predictors of L2 attainment.

This is a preview of subscription content, log in via an institution to check access.

Access this chapter

Subscribe and save.

• Get 10 units per month
• Download Article/Chapter or Ebook
• 1 Unit = 1 Article or 1 Chapter
• Cancel anytime
• Available as PDF
• Read on any device
• Instant download
• Own it forever
• Available as EPUB and PDF
• Compact, lightweight edition
• Dispatched in 3 to 5 business days
• Free shipping worldwide - see info
• Durable hardcover edition

Tax calculation will be finalised at checkout

Purchases are for personal use only

Institutional subscriptions

Similar content being viewed by others

Second Language Acquisition Research Methods

The Socio-educational Model of Second Language Acquisition

Granena and Long ( 2013 ) applied multiple linear regression analyses to the relationship of Chinese natives’ AoA to their attainment in L2 Spanish morphosyntax, phonology, and lexis and collocation. For each of these three linguistic domains, including breakpoints in the model revealed a small (5 %) but statistically significant increase in variance accounted for, as compared to the variance accounted for in a model with no breakpoints. According to the authors, the fact that the improvement was so small “could mean that the less complex (i.e. more parsimonious) model with no breakpoints is already a good enough fit to the data or, alternatively, that a larger sample size is needed to compensate for the loss of degrees of freedom and to minimize the risk of overfitting” (2013: 326–327).

DeKeyser ( 2000 : 515) erroneously reports that the correlation of years of schooling and GJ scores is r  = 0.006 ns, for early arrivals, and r  = 0.08 ns, for late arrivals. In fact, these reported coefficients reflect correlations of years of schooling with aptitude ; see discussion to follow.

Abrahamsson, N. and K. Hyltenstam. 2009. Age of onset and nativelikeness in a second language: Listener perception versus linguistic scrutiny. Language Learning 59: 249–306.

Google Scholar  

Ayer, A. J. 1959. History of the Logical Positivist movement. In Logical Positivism , ed. A. J. Ayer, 3–28. New York: Free Press.

Birdsong, D. 2005. Interpreting age effects in second language acquisition. In Handbook of bilingualism , eds. J. Kroll and A. DeGroot, 109–127. Oxford: Oxford University Press.

Birdsong, D. and M. Molis. 2001. On the evidence for maturational constraints in second-language acquisition. Journal of Memory and Language 44: 235–249.

Carroll, J. B. and S. M. Sapon. 1959. Modern Language Aptitude Test: Manual. New York: Psychological Corporation.

Cook, V. 2003. Effects of the second language on the first. Clevedon, UK: Multilingual Matters.

DeKeyser, R. M. 2000. The robustness of critical period effects in second language acquisition. Studies in Second Language Acquisition 22: 499–533.

DeKeyser, R., I. Alfi-Shabtay and D. Ravid. 2010. Cross-linguistic evidence for the nature of age effects in second language acquisition. Applied Psycholinguistics 31: 413–438.

Fowler, C. A., V. Sramko, D. J. Ostry, S. A. Rowland and P. Hallé. 2008. Cross language phonetic influences on the speech of French-English bilinguals. Journal of Phonetics 36: 649–663.

Granena, G. and M. H. Long. 2013. Age of onset, length of residence, language aptitude, and ultimate L2 attainment in three linguistic domains. Second Language Research 29: 311–343.

Hakuta, K., E. Bialystok and E. Wiley. 2003. Critical evidence: A test of the Critical-Period Hypothesis for second-language acquisition. Psychological Science 14: 31–38.

Hyltenstam, K. and N. Abrahamsson. 2003. Maturational constraints in SLA. The handbook of second language acquisition , eds. M. H. Long and C. J. Doughty, 539–588. Malden, MA: Blackwell.

Johnson, J. S. and E. L. Newport. 1989. Critical period effects in second language learning: The influence of maturational state on the acquisition of English as a second language. Cognitive Psychology 21: 60–99.

Lenneberg, E. H. 1967. Biological foundations of language. New York: Wiley.

Long, M. H. 1990. Maturational constraints on language development. Studies in Second Language Acquisition 12: 251–285.

Ortega, L. 2009. Understanding second language acquisition. London: Hodder Education.

Penfield, W. and L. Roberts. 1959. Speech and brain mechanisms. Princeton, NJ: Princeton University Press.

Popper, K. 1959. The logic of scientific discovery . New York: Basic Books.

Singleton, D. 2005. The Critical Period Hypothesis: A coat of many colours. International Review of Applied Linguistics in Language Teaching 43: 269–285.

Stevens, G. 2004. Using census data to test the critical-period hypothesis for second-language acquisition. Psychological Science 15: 215–216.

Vanhove, J. 2013. The critical period hypothesis in second language acquisition: A statistical critique and a reanalysis. PLoS ONE. 8(7): e69172. doi: 10.137/journal.pone.0069172

Download references

Author information

Authors and affiliations.

University of Texas at Austin, Texas, USA

David Birdsong

You can also search for this author in PubMed   Google Scholar

Corresponding author

Correspondence to David Birdsong .

Editor information

Editors and affiliations.

Faculty of Pedagogy and Fine Arts Dept. of English Studies, Adam Mickiewicz University, Kalisz, Wielkopolskie, Poland

Mirosław Pawlak

Graduate Studies Faculty, Oranim Academic College of Education, Tivon, Israel

Larissa Aronin

Rights and permissions

Reprints and permissions

Copyright information

© 2014 Springer International Publishing Switzerland

About this chapter

Birdsong, D. (2014). The Critical Period Hypothesis for Second Language Acquisition: Tailoring the Coat of Many Colors. In: Pawlak, M., Aronin, L. (eds) Essential Topics in Applied Linguistics and Multilingualism. Second Language Learning and Teaching. Springer, Cham. https://doi.org/10.1007/978-3-319-01414-2_3

Download citation

DOI : https://doi.org/10.1007/978-3-319-01414-2_3

Published : 19 September 2013

Publisher Name : Springer, Cham

Print ISBN : 978-3-319-01413-5

Online ISBN : 978-3-319-01414-2

eBook Packages : Humanities, Social Sciences and Law Education (R0)

Share this chapter

Anyone you share the following link with will be able to read this content:

Sorry, a shareable link is not currently available for this article.

Provided by the Springer Nature SharedIt content-sharing initiative

• Publish with us

Policies and ethics

• Find a journal
• Track your research

Click through the PLOS taxonomy to find articles in your field.

For more information about PLOS Subject Areas, click here .

Loading metrics

Open Access

Peer-reviewed

Research Article

The Critical Period Hypothesis in Second Language Acquisition: A Statistical Critique and a Reanalysis

* E-mail: [email protected]

Affiliation Department of Multilingualism, University of Fribourg, Fribourg, Switzerland

• Jan Vanhove

• Published: July 25, 2013
• https://doi.org/10.1371/journal.pone.0069172
• Reader Comments

17 Jul 2014: The PLOS ONE Staff (2014) Correction: The Critical Period Hypothesis in Second Language Acquisition: A Statistical Critique and a Reanalysis. PLOS ONE 9(7): e102922. https://doi.org/10.1371/journal.pone.0102922 View correction

In second language acquisition research, the critical period hypothesis ( cph ) holds that the function between learners' age and their susceptibility to second language input is non-linear. This paper revisits the indistinctness found in the literature with regard to this hypothesis's scope and predictions. Even when its scope is clearly delineated and its predictions are spelt out, however, empirical studies–with few exceptions–use analytical (statistical) tools that are irrelevant with respect to the predictions made. This paper discusses statistical fallacies common in cph research and illustrates an alternative analytical method (piecewise regression) by means of a reanalysis of two datasets from a 2010 paper purporting to have found cross-linguistic evidence in favour of the cph . This reanalysis reveals that the specific age patterns predicted by the cph are not cross-linguistically robust. Applying the principle of parsimony, it is concluded that age patterns in second language acquisition are not governed by a critical period. To conclude, this paper highlights the role of confirmation bias in the scientific enterprise and appeals to second language acquisition researchers to reanalyse their old datasets using the methods discussed in this paper. The data and R commands that were used for the reanalysis are provided as supplementary materials.

Citation: Vanhove J (2013) The Critical Period Hypothesis in Second Language Acquisition: A Statistical Critique and a Reanalysis. PLoS ONE 8(7): e69172. https://doi.org/10.1371/journal.pone.0069172

Editor: Stephanie Ann White, UCLA, United States of America

Received: May 7, 2013; Accepted: June 7, 2013; Published: July 25, 2013

Copyright: © 2013 Jan Vanhove. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: No current external funding sources for this study.

Competing interests: The author has declared that no competing interests exist.

Introduction

In the long term and in immersion contexts, second-language (L2) learners starting acquisition early in life – and staying exposed to input and thus learning over several years or decades – undisputedly tend to outperform later learners. Apart from being misinterpreted as an argument in favour of early foreign language instruction, which takes place in wholly different circumstances, this general age effect is also sometimes taken as evidence for a so-called ‘critical period’ ( cp ) for second-language acquisition ( sla ). Derived from biology, the cp concept was famously introduced into the field of language acquisition by Penfield and Roberts in 1959 [1] and was refined by Lenneberg eight years later [2] . Lenneberg argued that language acquisition needed to take place between age two and puberty – a period which he believed to coincide with the lateralisation process of the brain. (More recent neurological research suggests that different time frames exist for the lateralisation process of different language functions. Most, however, close before puberty [3] .) However, Lenneberg mostly drew on findings pertaining to first language development in deaf children, feral children or children with serious cognitive impairments in order to back up his claims. For him, the critical period concept was concerned with the implicit “automatic acquisition” [2, p. 176] in immersion contexts and does not preclude the possibility of learning a foreign language after puberty, albeit with much conscious effort and typically less success.

sla research adopted the critical period hypothesis ( cph ) and applied it to second and foreign language learning, resulting in a host of studies. In its most general version, the cph for sla states that the ‘susceptibility’ or ‘sensitivity’ to language input varies as a function of age, with adult L2 learners being less susceptible to input than child L2 learners. Importantly, the age–susceptibility function is hypothesised to be non-linear. Moving beyond this general version, we find that the cph is conceptualised in a multitude of ways [4] . This state of affairs requires scholars to make explicit their theoretical stance and assumptions [5] , but has the obvious downside that critical findings risk being mitigated as posing a problem to only one aspect of one particular conceptualisation of the cph , whereas other conceptualisations remain unscathed. This overall vagueness concerns two areas in particular, viz. the delineation of the cph 's scope and the formulation of testable predictions. Delineating the scope and formulating falsifiable predictions are, needless to say, fundamental stages in the scientific evaluation of any hypothesis or theory, but the lack of scholarly consensus on these points seems to be particularly pronounced in the case of the cph . This article therefore first presents a brief overview of differing views on these two stages. Then, once the scope of their cph version has been duly identified and empirical data have been collected using solid methods, it is essential that researchers analyse the data patterns soundly in order to assess the predictions made and that they draw justifiable conclusions from the results. As I will argue in great detail, however, the statistical analysis of data patterns as well as their interpretation in cph research – and this includes both critical and supportive studies and overviews – leaves a great deal to be desired. Reanalysing data from a recent cph -supportive study, I illustrate some common statistical fallacies in cph research and demonstrate how one particular cph prediction can be evaluated.

Delineating the scope of the critical period hypothesis

First, the age span for a putative critical period for language acquisition has been delimited in different ways in the literature [4] . Lenneberg's critical period stretched from two years of age to puberty (which he posits at about 14 years of age) [2] , whereas other scholars have drawn the cutoff point at 12, 15, 16 or 18 years of age [6] . Unlike Lenneberg, most researchers today do not define a starting age for the critical period for language learning. Some, however, consider the possibility of the critical period (or a critical period for a specific language area, e.g. phonology) ending much earlier than puberty (e.g. age 9 years [1] , or as early as 12 months in the case of phonology [7] ).

Second, some vagueness remains as to the setting that is relevant to the cph . Does the critical period constrain implicit learning processes only, i.e. only the untutored language acquisition in immersion contexts or does it also apply to (at least partly) instructed learning? Most researchers agree on the former [8] , but much research has included subjects who have had at least some instruction in the L2.

Third, there is no consensus on what the scope of the cp is as far as the areas of language that are concerned. Most researchers agree that a cp is most likely to constrain the acquisition of pronunciation and grammar and, consequently, these are the areas primarily looked into in studies on the cph [9] . Some researchers have also tried to define distinguishable cp s for the different language areas of phonetics, morphology and syntax and even for lexis (see [10] for an overview).

Fourth and last, research into the cph has focused on ‘ultimate attainment’ ( ua ) or the ‘final’ state of L2 proficiency rather than on the rate of learning. From research into the rate of acquisition (e.g. [11] – [13] ), it has become clear that the cph cannot hold for the rate variable. In fact, it has been observed that adult learners proceed faster than child learners at the beginning stages of L2 acquisition. Though theoretical reasons for excluding the rate can be posited (the initial faster rate of learning in adults may be the result of more conscious cognitive strategies rather than to less conscious implicit learning, for instance), rate of learning might from a different perspective also be considered an indicator of ‘susceptibility’ or ‘sensitivity’ to language input. Nevertheless, contemporary sla scholars generally seem to concur that ua and not rate of learning is the dependent variable of primary interest in cph research. These and further scope delineation problems relevant to cph research are discussed in more detail by, among others, Birdsong [9] , DeKeyser and Larson-Hall [14] , Long [10] and Muñoz and Singleton [6] .

Formulating testable hypotheses

Once the relevant cph 's scope has satisfactorily been identified, clear and testable predictions need to be drawn from it. At this stage, the lack of consensus on what the consequences or the actual observable outcome of a cp would have to look like becomes evident. As touched upon earlier, cph research is interested in the end state or ‘ultimate attainment’ ( ua ) in L2 acquisition because this “determines the upper limits of L2 attainment” [9, p. 10]. The range of possible ultimate attainment states thus helps researchers to explore the potential maximum outcome of L2 proficiency before and after the putative critical period.

One strong prediction made by some cph exponents holds that post- cp learners cannot reach native-like L2 competences. Identifying a single native-like post- cp L2 learner would then suffice to falsify all cph s making this prediction. Assessing this prediction is difficult, however, since it is not clear what exactly constitutes sufficient nativelikeness, as illustrated by the discussion on the actual nativelikeness of highly accomplished L2 speakers [15] , [16] . Indeed, there exists a real danger that, in a quest to vindicate the cph , scholars set the bar for L2 learners to match monolinguals increasingly higher – up to Swiftian extremes. Furthermore, the usefulness of comparing the linguistic performance in mono- and bilinguals has been called into question [6] , [17] , [18] . Put simply, the linguistic repertoires of mono- and bilinguals differ by definition and differences in the behavioural outcome will necessarily be found, if only one digs deep enough.

A second strong prediction made by cph proponents is that the function linking age of acquisition and ultimate attainment will not be linear throughout the whole lifespan. Before discussing how this function would have to look like in order for it to constitute cph -consistent evidence, I point out that the ultimate attainment variable can essentially be considered a cumulative measure dependent on the actual variable of interest in cph research, i.e. susceptibility to language input, as well as on such other factors like duration and intensity of learning (within and outside a putative cp ) and possibly a number of other influencing factors. To elaborate, the behavioural outcome, i.e. ultimate attainment, can be assumed to be integrative to the susceptibility function, as Newport [19] correctly points out. Other things being equal, ultimate attainment will therefore decrease as susceptibility decreases. However, decreasing ultimate attainment levels in and by themselves represent no compelling evidence in favour of a cph . The form of the integrative curve must therefore be predicted clearly from the susceptibility function. Additionally, the age of acquisition–ultimate attainment function can take just about any form when other things are not equal, e.g. duration of learning (Does learning last up until time of testing or only for a more or less constant number of years or is it dependent on age itself?) or intensity of learning (Do learners always learn at their maximum susceptibility level or does this intensity vary as a function of age, duration, present attainment and motivation?). The integral of the susceptibility function could therefore be of virtually unlimited complexity and its parameters could be adjusted to fit any age of acquisition–ultimate attainment pattern. It seems therefore astonishing that the distinction between level of sensitivity to language input and level of ultimate attainment is rarely made in the literature. Implicitly or explicitly [20] , the two are more or less equated and the same mathematical functions are expected to describe the two variables if observed across a range of starting ages of acquisition.

But even when the susceptibility and ultimate attainment variables are equated, there remains controversy as to what function linking age of onset of acquisition and ultimate attainment would actually constitute evidence for a critical period. Most scholars agree that not any kind of age effect constitutes such evidence. More specifically, the age of acquisition–ultimate attainment function would need to be different before and after the end of the cp [9] . According to Birdsong [9] , three basic possible patterns proposed in the literature meet this condition. These patterns are presented in Figure 1 . The first pattern describes a steep decline of the age of onset of acquisition ( aoa )–ultimate attainment ( ua ) function up to the end of the cp and a practically non-existent age effect thereafter. Pattern 2 is an “unconventional, although often implicitly invoked” [9, p. 17] notion of the cp function which contains a period of peak attainment (or performance at ceiling), i.e. performance does not vary as a function of age, which is often referred to as a ‘window of opportunity’. This time span is followed by an unbounded decline in ua depending on aoa . Pattern 3 includes characteristics of patterns 1 and 2. At the beginning of the aoa range, performance is at ceiling. The next segment is a downward slope in the age function which ends when performance reaches its floor. Birdsong points out that all of these patterns have been reported in the literature. On closer inspection, however, he concludes that the most convincing function describing these age effects is a simple linear one. Hakuta et al. [21] sketch further theoretically possible predictions of the cph in which the mean performance drops drastically and/or the slope of the aoa – ua proficiency function changes at a certain point.

• PPT PowerPoint slide
• PNG larger image
• TIFF original image

The graphs are based on based on Figure 2 in [9] .

https://doi.org/10.1371/journal.pone.0069172.g001

Although several patterns have been proposed in the literature, it bears pointing out that the most common explicit prediction corresponds to Birdsong's first pattern, as exemplified by the following crystal-clear statement by DeKeyser, one of the foremost cph proponents:

[A] strong negative correlation between age of acquisition and ultimate attainment throughout the lifespan (or even from birth through middle age), the only age effect documented in many earlier studies, is not evidence for a critical period…[T]he critical period concept implies a break in the AoA–proficiency function, i.e., an age (somewhat variable from individual to individual, of course, and therefore an age range in the aggregate) after which the decline of success rate in one or more areas of language is much less pronounced and/or clearly due to different reasons. [22, p. 445].

DeKeyser and before him among others Johnson and Newport [23] thus conceptualise only one possible pattern which would speak in favour of a critical period: a clear negative age effect before the end of the critical period and a much weaker (if any) negative correlation between age and ultimate attainment after it. This ‘flattened slope’ prediction has the virtue of being much more tangible than the ‘potential nativelikeness’ prediction: Testing it does not necessarily require comparing the L2-learners to a native control group and thus effectively comparing apples and oranges. Rather, L2-learners with different aoa s can be compared amongst themselves without the need to categorise them by means of a native-speaker yardstick, the validity of which is inevitably going to be controversial [15] . In what follows, I will concern myself solely with the ‘flattened slope’ prediction, arguing that, despite its clarity of formulation, cph research has generally used analytical methods that are irrelevant for the purposes of actually testing it.

Inferring non-linearities in critical period research: An overview

Group mean or proportion comparisons.

[T]he main differences can be found between the native group and all other groups – including the earliest learner group – and between the adolescence group and all other groups. However, neither the difference between the two childhood groups nor the one between the two adulthood groups reached significance, which indicates that the major changes in eventual perceived nativelikeness of L2 learners can be associated with adolescence. [15, p. 270].

Similar group comparisons aimed at investigating the effect of aoa on ua have been carried out by both cph advocates and sceptics (among whom Bialystok and Miller [25, pp. 136–139], Birdsong and Molis [26, p. 240], Flege [27, pp. 120–121], Flege et al. [28, pp. 85–86], Johnson [29, p. 229], Johnson and Newport [23, p. 78], McDonald [30, pp. 408–410] and Patowski [31, pp. 456–458]). To be clear, not all of these authors drew direct conclusions about the aoa – ua function on the basis of these groups comparisons, but their group comparisons have been cited as indicative of a cph -consistent non-continuous age effect, as exemplified by the following quote by DeKeyser [22] :

Where group comparisons are made, younger learners always do significantly better than the older learners. The behavioral evidence, then, suggests a non-continuous age effect with a “bend” in the AoA–proficiency function somewhere between ages 12 and 16. [22, p. 448].

The first problem with group comparisons like these and drawing inferences on the basis thereof is that they require that a continuous variable, aoa , be split up into discrete bins. More often than not, the boundaries between these bins are drawn in an arbitrary fashion, but what is more troublesome is the loss of information and statistical power that such discretisation entails (see [32] for the extreme case of dichotomisation). If we want to find out more about the relationship between aoa and ua , why throw away most of the aoa information and effectively reduce the ua data to group means and the variance in those groups?

Comparison of correlation coefficients.

Correlation-based inferences about slope discontinuities have similarly explicitly been made by cph advocates and skeptics alike, e.g. Bialystok and Miller [25, pp. 136 and 140], DeKeyser and colleagues [22] , [44] and Flege et al. [45, pp. 166 and 169]. Others did not explicitly infer the presence or absence of slope differences from the subset correlations they computed (among others Birdsong and Molis [26] , DeKeyser [8] , Flege et al. [28] and Johnson [29] ), but their studies nevertheless featured in overviews discussing discontinuities [14] , [22] . Indeed, the most recent overview draws a strong conclusion about the validity of the cph 's ‘flattened slope’ prediction on the basis of these subset correlations:

In those studies where the two groups are described separately, the correlation is much higher for the younger than for the older group, except in Birdsong and Molis (2001) [ =  [26] , JV], where there was a ceiling effect for the younger group. This global picture from more than a dozen studies provides support for the non-continuity of the decline in the AoA–proficiency function, which all researchers agree is a hallmark of a critical period phenomenon. [22, p. 448].

In Johnson and Newport's specific case [23] , their correlation-based inference that ua levels off after puberty happened to be largely correct: the gjt scores are more or less randomly distributed around a near-horizontal trend line [26] . Ultimately, however, it rests on the fallacy of confusing correlation coefficients with slopes, which seriously calls into question conclusions such as DeKeyser's (cf. the quote above).

https://doi.org/10.1371/journal.pone.0069172.g002

Lower correlation coefficients in older aoa groups may therefore be largely due to differences in ua variance, which have been reported in several studies [23] , [26] , [28] , [29] (see [46] for additional references). Greater variability in ua with increasing age is likely due to factors other than age proper [47] , such as the concomitant greater variability in exposure to literacy, degree of education, motivation and opportunity for language use, and by itself represents evidence neither in favour of nor against the cph .

Regression approaches.

Having demonstrated that neither group mean or proportion comparisons nor correlation coefficient comparisons can directly address the ‘flattened slope’ prediction, I now turn to the studies in which regression models were computed with aoa as a predictor variable and ua as the outcome variable. Once again, this category of studies is not mutually exclusive with the two categories discussed above.

In a large-scale study using self-reports and approximate aoa s derived from a sample of the 1990 U.S. Census, Stevens found that the probability with which immigrants from various countries stated that they spoke English ‘very well’ decreased curvilinearly as a function of aoa [48] . She noted that this development is similar to the pattern found by Johnson and Newport [23] but that it contains no indication of an “abruptly defined ‘critical’ or sensitive period in L2 learning” [48, p. 569]. However, she modelled the self-ratings using an ordinal logistic regression model in which the aoa variable was logarithmically transformed. Technically, this is perfectly fine, but one should be careful not to read too much into the non-linear curves found. In logistic models, the outcome variable itself is modelled linearly as a function of the predictor variables and is expressed in log-odds. In order to compute the corresponding probabilities, these log-odds are transformed using the logistic function. Consequently, even if the model is specified linearly, the predicted probabilities will not lie on a perfectly straight line when plotted as a function of any one continuous predictor variable. Similarly, when the predictor variable is first logarithmically transformed and then used to linearly predict an outcome variable, the function linking the predicted outcome variables and the untransformed predictor variable is necessarily non-linear. Thus, non-linearities follow naturally from Stevens's model specifications. Moreover, cph -consistent discontinuities in the aoa – ua function cannot be found using her model specifications as they did not contain any parameters allowing for this.

Using data similar to Stevens's, Bialystok and Hakuta found that the link between the self-rated English competences of Chinese- and Spanish-speaking immigrants and their aoa could be described by a straight line [49] . In contrast to Stevens, Bialystok and Hakuta used a regression-based method allowing for changes in the function's slope, viz. locally weighted scatterplot smoothing ( lowess ). Informally, lowess is a non-parametrical method that relies on an algorithm that fits the dependent variable for small parts of the range of the independent variable whilst guaranteeing that the overall curve does not contain sudden jumps (for technical details, see [50] ). Hakuta et al. used an even larger sample from the same 1990 U.S. Census data on Chinese- and Spanish-speaking immigrants (2.3 million observations) [21] . Fitting lowess curves, no discontinuities in the aoa – ua slope could be detected. Moreover, the authors found that piecewise linear regression models, i.e. regression models containing a parameter that allows a sudden drop in the curve or a change of its slope, did not provide a better fit to the data than did an ordinary regression model without such a parameter.

To sum up, I have argued at length that regression approaches are superior to group mean and correlation coefficient comparisons for the purposes of testing the ‘flattened slope’ prediction. Acknowledging the reservations vis-à-vis self-estimated ua s, we still find that while the relationship between aoa and ua is not necessarily perfectly linear in the studies discussed, the data do not lend unequivocal support to this prediction. In the following section, I will reanalyse data from a recent empirical paper on the cph by DeKeyser et al. [44] . The first goal of this reanalysis is to further illustrate some of the statistical fallacies encountered in cph studies. Second, by making the computer code available I hope to demonstrate how the relevant regression models, viz. piecewise regression models, can be fitted and how the aoa representing the optimal breakpoint can be identified. Lastly, the findings of this reanalysis will contribute to our understanding of how aoa affects ua as measured using a gjt .

Summary of DeKeyser et al. (2010)

I chose to reanalyse a recent empirical paper on the cph by DeKeyser et al. [44] (henceforth DK et al.). This paper lends itself well to a reanalysis since it exhibits two highly commendable qualities: the authors spell out their hypotheses lucidly and provide detailed numerical and graphical data descriptions. Moreover, the paper's lead author is very clear on what constitutes a necessary condition for accepting the cph : a non-linearity in the age of onset of acquisition ( aoa )–ultimate attainment ( ua ) function, with ua declining less strongly as a function of aoa in older, post- cp arrivals compared to younger arrivals [14] , [22] . Lastly, it claims to have found cross-linguistic evidence from two parallel studies backing the cph and should therefore be an unsuspected source to cph proponents.

The authors set out to test the following hypotheses:

• Hypothesis 1: For both the L2 English and the L2 Hebrew group, the slope of the age of arrival–ultimate attainment function will not be linear throughout the lifespan, but will instead show a marked flattening between adolescence and adulthood.
• Hypothesis 2: The relationship between aptitude and ultimate attainment will differ markedly for the young and older arrivals, with significance only for the latter. (DK et al., p. 417)

Both hypotheses were purportedly confirmed, which in the authors' view provides evidence in favour of cph . The problem with this conclusion, however, is that it is based on a comparison of correlation coefficients. As I have argued above, correlation coefficients are not to be confused with regression coefficients and cannot be used to directly address research hypotheses concerning slopes, such as Hypothesis 1. In what follows, I will reanalyse the relationship between DK et al.'s aoa and gjt data in order to address Hypothesis 1. Additionally, I will lay bare a problem with the way in which Hypothesis 2 was addressed. The extracted data and the computer code used for the reanalysis are provided as supplementary materials, allowing anyone interested to scrutinise and easily reproduce my whole analysis and carry out their own computations (see ‘supporting information’).

Data extraction

In order to verify whether we did in fact extract the data points to a satisfactory degree of accuracy, I computed summary statistics for the extracted aoa and gjt data and checked these against the descriptive statistics provided by DK et al. (pp. 421 and 427). These summary statistics for the extracted data are presented in Table 1 . In addition, I computed the correlation coefficients for the aoa – gjt relationship for the whole aoa range and for aoa -defined subgroups and checked these coefficients against those reported by DK et al. (pp. 423 and 428). The correlation coefficients computed using the extracted data are presented in Table 2 . Both checks strongly suggest the extracted data to be virtually identical to the original data, and Dr DeKeyser confirmed this to be the case in response to an earlier draft of the present paper (personal communication, 6 May 2013).

https://doi.org/10.1371/journal.pone.0069172.t001

https://doi.org/10.1371/journal.pone.0069172.t002

Results and Discussion

Modelling the link between age of onset of acquisition and ultimate attainment.

I first replotted the aoa and gjt data we extracted from DK et al.'s scatterplots and added non-parametric scatterplot smoothers in order to investigate whether any changes in slope in the aoa – gjt function could be revealed, as per Hypothesis 1. Figures 3 and 4 show this not to be the case. Indeed, simple linear regression models that model gjt as a function of aoa provide decent fits for both the North America and the Israel data, explaining 65% and 63% of the variance in gjt scores, respectively. The parameters of these models are given in Table 3 .

The trend line is a non-parametric scatterplot smoother. The scatterplot itself is a near-perfect replication of DK et al.'s Fig. 1.

https://doi.org/10.1371/journal.pone.0069172.g003

The trend line is a non-parametric scatterplot smoother. The scatterplot itself is a near-perfect replication of DK et al.'s Fig. 5.

https://doi.org/10.1371/journal.pone.0069172.g004

https://doi.org/10.1371/journal.pone.0069172.t003

To ensure that both segments are joined at the breakpoint, the predictor variable is first centred at the breakpoint value, i.e. the breakpoint value is subtracted from the original predictor variable values. For a blow-by-blow account of how such models can be fitted in r , I refer to an example analysis by Baayen [55, pp. 214–222].

Solid: regression with breakpoint at aoa 18 (dashed lines represent its 95% confidence interval); dot-dash: regression without breakpoint.

https://doi.org/10.1371/journal.pone.0069172.g005

Solid: regression with breakpoint at aoa 18 (dashed lines represent its 95% confidence interval); dot-dash (hardly visible due to near-complete overlap): regression without breakpoint.

https://doi.org/10.1371/journal.pone.0069172.g006

https://doi.org/10.1371/journal.pone.0069172.t004

https://doi.org/10.1371/journal.pone.0069172.g007

Solid: regression with breakpoint at aoa 16 (dashed lines represent its 95% confidence interval); dot-dash: regression without breakpoint.

https://doi.org/10.1371/journal.pone.0069172.g008

Solid: regression with breakpoint at aoa 6 (dashed lines represent its 95% confidence interval); dot-dash (hardly visible due to near-complete overlap): regression without breakpoint.

https://doi.org/10.1371/journal.pone.0069172.g009

https://doi.org/10.1371/journal.pone.0069172.t005

https://doi.org/10.1371/journal.pone.0069172.t006

https://doi.org/10.1371/journal.pone.0069172.t007

https://doi.org/10.1371/journal.pone.0069172.t008

In sum, a regression model that allows for changes in the slope of the the aoa – gjt function to account for putative critical period effects provides a somewhat better fit to the North American data than does an everyday simple regression model. The improvement in model fit is marginal, however, and including a breakpoint does not result in any detectable improvement of model fit to the Israel data whatsoever. Breakpoint models therefore fail to provide solid cross-linguistic support in favour of critical period effects: across both data sets, gjt can satisfactorily be modelled as a linear function of aoa .

On partialling out ‘age at testing’

As I have argued above, correlation coefficients cannot be used to test hypotheses about slopes. When the correct procedure is carried out on DK et al.'s data, no cross-linguistically robust evidence for changes in the aoa – gjt function was found. In addition to comparing the zero-order correlations between aoa and gjt , however, DK et al. computed partial correlations in which the variance in aoa associated with the participants' age at testing ( aat ; a potentially confounding variable) was filtered out. They found that these partial correlations between aoa and gjt , which are given in Table 9 , differed between age groups in that they are stronger for younger than for older participants. This, DK et al. argue, constitutes additional evidence in favour of the cph . At this point, I can no longer provide my own analysis of DK et al.'s data seeing as the pertinent data points were not plotted. Nevertheless, the detailed descriptions by DK et al. strongly suggest that the use of these partial correlations is highly problematic. Most importantly, and to reiterate, correlations (whether zero-order or partial ones) are actually of no use when testing hypotheses concerning slopes. Still, one may wonder why the partial correlations differ across age groups. My surmise is that these differences are at least partly the by-product of an imbalance in the sampling procedure.

https://doi.org/10.1371/journal.pone.0069172.t009

The upshot of this brief discussion is that the partial correlation differences reported by DK et al. are at least partly the result of an imbalance in the sampling procedure: aoa and aat were simply less intimately tied for the young arrivals in the North America study than for the older arrivals with L2 English or for all of the L2 Hebrew participants. In an ideal world, we would like to fix aat or ascertain that it at most only weakly correlates with aoa . This, however, would result in a strong correlation between aoa and another potential confound variable, length of residence in the L2 environment, bringing us back to square one. Allowing for only moderate correlations between aoa and aat might improve our predicament somewhat, but even in that case, we should tread lightly when making inferences on the basis of statistical control procedures [61] .

On estimating the role of aptitude

Having shown that Hypothesis 1 could not be confirmed, I now turn to Hypothesis 2, which predicts a differential role of aptitude for ua in sla in different aoa groups. More specifically, it states that the correlation between aptitude and gjt performance will be significant only for older arrivals. The correlation coefficients of the relationship between aptitude and gjt are presented in Table 10 .

https://doi.org/10.1371/journal.pone.0069172.t010

The problem with both the wording of Hypothesis 2 and the way in which it is addressed is the following: it is assumed that a variable has a reliably different effect in different groups when the effect reaches significance in one group but not in the other. This logic is fairly widespread within several scientific disciplines (see e.g. [62] for a discussion). Nonetheless, it is demonstrably fallacious [63] . Here we will illustrate the fallacy for the specific case of comparing two correlation coefficients.

Apart from not being replicated in the North America study, does this difference actually show anything? I contend that it does not: what is of interest are not so much the correlation coefficients, but rather the interactions between aoa and aptitude in models predicting gjt . These interactions could be investigated by fitting a multiple regression model in which the postulated cp breakpoint governs the slope of both aoa and aptitude. If such a model provided a substantially better fit to the data than a model without a breakpoint for the aptitude slope and if the aptitude slope changes in the expected direction (i.e. a steeper slope for post- cp than for younger arrivals) for different L1–L2 pairings, only then would this particular prediction of the cph be borne out.

Using data extracted from a paper reporting on two recent studies that purport to provide evidence in favour of the cph and that, according to its authors, represent a major improvement over earlier studies (DK et al., p. 417), it was found that neither of its two hypotheses were actually confirmed when using the proper statistical tools. As a matter of fact, the gjt scores continue to decline at essentially the same rate even beyond the end of the putative critical period. According to the paper's lead author, such a finding represents a serious problem to his conceptualisation of the cph [14] ). Moreover, although modelling a breakpoint representing the end of a cp at aoa 16 may improve the statistical model slightly in study on learners of English in North America, the study on learners of Hebrew in Israel fails to confirm this finding. In fact, even if we were to accept the optimal breakpoint computed for the Israel study, it lies at aoa 6 and is associated with a different geometrical pattern.

Diverging age trends in parallel studies with participants with different L2s have similarly been reported by Birdsong and Molis [26] and are at odds with an L2-independent cph . One parsimonious explanation of such conflicting age trends may be that the overall, cross-linguistic age trend is in fact linear, but that fluctuations in the data (due to factors unaccounted for or randomness) may sometimes give rise to a ‘stretched L’-shaped pattern ( Figure 1, left panel ) and sometimes to a ‘stretched 7’-shaped pattern ( Figure 1 , middle panel; see also [66] for a similar comment).

Importantly, the criticism that DeKeyser and Larsson-Hall levy against two studies reporting findings similar to the present [48] , [49] , viz. that the data consisted of self-ratings of questionable validity [14] , does not apply to the present data set. In addition, DK et al. did not exclude any outliers from their analyses, so I assume that DeKeyser and Larsson-Hall's criticism [14] of Birdsong and Molis's study [26] , i.e. that the findings were due to the influence of outliers, is not applicable to the present data either. For good measure, however, I refitted the regression models with and without breakpoints after excluding one potentially problematic data point per model. The following data points had absolute standardised residuals larger than 2.5 in the original models without breakpoints as well as in those with breakpoints: the participant with aoa 17 and a gjt score of 125 in the North America study and the participant with aoa 12 and a gjt score of 117 in the Israel study. The resultant models were virtually identical to the original models (see Script S1 ). Furthermore, the aoa variable was sufficiently fine-grained and the aoa – gjt curve was not ‘presmoothed’ by the prior aggregation of gjt across parts of the aoa range (see [51] for such a criticism of another study). Lastly, seven of the nine “problems with supposed counter-evidence” to the cph discussed by Long [5] do not apply either, viz. (1) “[c]onfusion of rate and ultimate attainment”, (2) “[i]nappropriate choice of subjects”, (3) “[m]easurement of AO”, (4) “[l]eading instructions to raters”, (6) “[u]se of markedly non-native samples making near-native samples more likely to sound native to raters”, (7) “[u]nreliable or invalid measures”, and (8) “[i]nappropriate L1–L2 pairings”. Problem No. 5 (“Assessments based on limited samples and/or “language-like” behavior”) may be apropos given that only gjt data were used, leaving open the theoretical possibility that other measures might have yielded a different outcome. Finally, problem No. 9 (“Faulty interpretation of statistical patterns”) is, of course, precisely what I have turned the spotlights on.

Conclusions

The critical period hypothesis remains a hotly contested issue in the psycholinguistics of second-language acquisition. Discussions about the impact of empirical findings on the tenability of the cph generally revolve around the reliability of the data gathered (e.g. [5] , [14] , [22] , [52] , [67] , [68] ) and such methodological critiques are of course highly desirable. Furthermore, the debate often centres on the question of exactly what version of the cph is being vindicated or debunked. These versions differ mainly in terms of its scope, specifically with regard to the relevant age span, setting and language area, and the testable predictions they make. But even when the cph 's scope is clearly demarcated and its main prediction is spelt out lucidly, the issue remains to what extent the empirical findings can actually be marshalled in support of the relevant cph version. As I have shown in this paper, empirical data have often been taken to support cph versions predicting that the relationship between age of acquisition and ultimate attainment is not strictly linear, even though the statistical tools most commonly used (notably group mean and correlation coefficient comparisons) were, crudely put, irrelevant to this prediction. Methods that are arguably valid, e.g. piecewise regression and scatterplot smoothing, have been used in some studies [21] , [26] , [49] , but these studies have been criticised on other grounds. To my knowledge, such methods have never been used by scholars who explicitly subscribe to the cph .

I suspect that what may be going on is a form of ‘confirmation bias’ [69] , a cognitive bias at play in diverse branches of human knowledge seeking: Findings judged to be consistent with one's own hypothesis are hardly questioned, whereas findings inconsistent with one's own hypothesis are scrutinised much more strongly and criticised on all sorts of points [70] – [73] . My reanalysis of DK et al.'s recent paper may be a case in point. cph exponents used correlation coefficients to address their prediction about the slope of a function, as had been done in a host of earlier studies. Finding a result that squared with their expectations, they did not question the technical validity of their results, or at least they did not report this. (In fact, my reanalysis is actually a case in point in two respects: for an earlier draft of this paper, I had computed the optimal position of the breakpoints incorrectly, resulting in an insignificant improvement of model fit for the North American data rather than a borderline significant one. Finding a result that squared with my expectations, I did not question the technical validity of my results – until this error was kindly pointed out to me by Martijn Wieling (University of Tübingen).) That said, I am keen to point out that the statistical analyses in this particular paper, though suboptimal, are, as far as I could gather, reported correctly, i.e. the confirmation bias does not seem to have resulted in the blatant misreportings found elsewhere (see [74] for empirical evidence and discussion). An additional point to these authors' credit is that, apart from explicitly identifying their cph version's scope and making crystal-clear predictions, they present data descriptions that actually permit quantitative reassessments and have a history of doing so (e.g. the appendix in [8] ). This leads me to believe that they analysed their data all in good conscience and to hope that they, too, will conclude that their own data do not, in fact, support their hypothesis.

I end this paper on an upbeat note. Even though I have argued that the analytical tools employed in cph research generally leave much to be desired, the original data are, so I hope, still available. This provides researchers, cph supporters and sceptics alike, with an exciting opportunity to reanalyse their data sets using the tools outlined in the present paper and publish their findings at minimal cost of time and resources (for instance, as a comment to this paper). I would therefore encourage scholars to engage their old data sets and to communicate their analyses openly, e.g. by voluntarily publishing their data and computer code alongside their articles or comments. Ideally, cph supporters and sceptics would join forces to agree on a protocol for a high-powered study in order to provide a truly convincing answer to a core issue in sla .

Supporting Information

Dataset s1..

aoa and gjt data extracted from DeKeyser et al.'s North America study.

https://doi.org/10.1371/journal.pone.0069172.s001

Dataset S2.

aoa and gjt data extracted from DeKeyser et al.'s Israel study.

https://doi.org/10.1371/journal.pone.0069172.s002

Script with annotated R code used for the reanalysis. All add-on packages used can be installed from within R.

https://doi.org/10.1371/journal.pone.0069172.s003

Acknowledgments

I would like to thank Irmtraud Kaiser (University of Fribourg) for helping me to get an overview of the literature on the critical period hypothesis in second language acquisition. Thanks are also due to Martijn Wieling (currently University of Tübingen) for pointing out an error in the R code accompanying an earlier draft of this paper.

Author Contributions

Analyzed the data: JV. Wrote the paper: JV.

• 1. Penfield W, Roberts L (1959) Speech and brain mechanisms. Princeton: Princeton University Press.
• 2. Lenneberg EH (1967) Biological foundations of language. New York: Wiley.
• View Article
• Google Scholar
• 10. Long MH (2007) Problems in SLA. Mahwah, NJ: Lawrence Erlbaum.
• 14. DeKeyser R, Larson-Hall J (2005) What does the critical period really mean? In: Kroll and De Groot [75], 88–108.
• 19. Newport EL (1991) Contrasting conceptions of the critical period for language. In: Carey S, Gelman R, editors, The epigenesis of mind: Essays on biology and cognition, Hillsdale, NJ: Lawrence Erlbaum. 111–130.
• 20. Birdsong D (2005) Interpreting age effects in second language acquisition. In: Kroll and De Groot [75], 109–127.
• 22. DeKeyser R (2012) Age effects in second language learning. In: Gass SM, Mackey A, editors, The Routledge handbook of second language acquisition, London: Routledge. 442–460.
• 24. Weisstein EW. Discontinuity. From MathWorld –A Wolfram Web Resource. Available: http://mathworld.wolfram.com/Discontinuity.html . Accessed 2012 March 2.
• 27. Flege JE (1999) Age of learning and second language speech. In: Birdsong [76], 101–132.
• 36. Champely S (2009) pwr: Basic functions for power analysis. Available: http://cran.r-project.org/package=pwr . R package, version 1.1.1.
• 37. R Core Team (2013) R: A language and environment for statistical computing. Available: http://www.r-project.org/ . Software, version 2.15.3.
• 47. Hyltenstam K, Abrahamsson N (2003) Maturational constraints in sla . In: Doughty CJ, Long MH, editors, The handbook of second language acquisition, Malden, MA: Blackwell. 539–588.
• 49. Bialystok E, Hakuta K (1999) Confounded age: Linguistic and cognitive factors in age differences for second language acquisition. In: Birdsong [76], 161–181.
• 52. DeKeyser R (2006) A critique of recent arguments against the critical period hypothesis. In: Abello-Contesse C, Chacón-Beltrán R, López-Jiménez MD, Torreblanca-López MM, editors, Age in L2 acquisition and teaching, Bern: Peter Lang. 49–58.
• 55. Baayen RH (2008) Analyzing linguistic data: A practical introduction to statistics using R. Cambridge: Cambridge University Press.
• 56. Fox J (2002) Robust regression. Appendix to An R and S-Plus Companion to Applied Regression. Available: http://cran.r-project.org/doc/contrib/Fox-Companion/appendix.html .
• 57. Ripley B, Hornik K, Gebhardt A, Firth D (2012) MASS: Support functions and datasets for Venables and Ripley's MASS. Available: http://cran.r-project.org/package=MASS . R package, version 7.3–17.
• 58. Zuur AF, Ieno EN, Walker NJ, Saveliev AA, Smith GM (2009) Mixed effects models and extensions in ecology with R. New York: Springer.
• 59. Pinheiro J, Bates D, DebRoy S, Sarkar D, R Core Team (2013) nlme: Linear and nonlinear mixed effects models. Available: http://cran.r-project.org/package=nlme . R package, version 3.1–108.
• 65. Field A (2009) Discovering statistics using SPSS. London: SAGE 3rd edition.
• 66. Birdsong D (2009) Age and the end state of second language acquisition. In: Ritchie WC, Bhatia TK, editors, The new handbook of second language acquisition, Bingley: Emerlad. 401–424.
• 75. Kroll JF, De Groot AMB, editors (2005) Handbook of bilingualism: Psycholinguistic approaches. New York: Oxford University Press.
• 76. Birdsong D, editor (1999) Second language acquisition and the critical period hypothesis. Mahwah, NJ: Lawrence Erlbaum.

Information

• Author Services

Initiatives

You are accessing a machine-readable page. In order to be human-readable, please install an RSS reader.

All articles published by MDPI are made immediately available worldwide under an open access license. No special permission is required to reuse all or part of the article published by MDPI, including figures and tables. For articles published under an open access Creative Common CC BY license, any part of the article may be reused without permission provided that the original article is clearly cited. For more information, please refer to https://www.mdpi.com/openaccess .

Feature papers represent the most advanced research with significant potential for high impact in the field. A Feature Paper should be a substantial original Article that involves several techniques or approaches, provides an outlook for future research directions and describes possible research applications.

Feature papers are submitted upon individual invitation or recommendation by the scientific editors and must receive positive feedback from the reviewers.

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

Original Submission Date Received: .

• Active Journals
• Find a Journal
• Proceedings Series
• For Authors
• For Reviewers
• For Editors
• For Librarians
• For Publishers
• For Societies
• For Conference Organizers
• Open Access Policy
• Institutional Open Access Program
• Special Issues Guidelines
• Editorial Process
• Research and Publication Ethics
• Article Processing Charges
• Testimonials
• Preprints.org
• SciProfiles
• Encyclopedia

Article Menu

• Subscribe SciFeed
• Recommended Articles
• Google Scholar
• on Google Scholar
• Table of Contents

Find support for a specific problem in the support section of our website.

Please let us know what you think of our products and services.

Visit our dedicated information section to learn more about MDPI.

JSmol Viewer

The critical period hypothesis for l2 acquisition: an unfalsifiable embarrassment.

1. Introduction

2. the notion of critical period, 3. cph or cphs, 4. problems with the “scrutinized nativelikeness” yardstick, 5. aptitude.

Although language-learning aptitude might seem to be a relatively stable individual characteristic when compared with other factors, such as motivational orientation and action control mechanisms, there seems to be some converging evidence that certain components of aptitude … might improve in the course of language learning.

6. Age or Opportunity?

7. looking for discontinuity, 8. neurolinguistics: new developments, 9. concluding remarks, author contributions, institutional review board statement, informed consent statement, data availability statement, conflicts of interest.

• Abdel Aal, Alaa. 2016. Delayed puberty. Human Andrology 6: 27–30. [ Google Scholar ] [ CrossRef ]
• Abrahamsson, Niclas, and Kenneth Hyltenstam. 2008. The robustness of aptitude effects in near-native second language acquisition. Studies in Second Language Acquisition 30: 481–509. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Abrahamsson, Niclas, and Kenneth Hyltenstam. 2009. Age of onset and nativelikeness in a second language: Listener perception versus linguistic scrutiny. Language Learning 59: 249–306. [ Google Scholar ]
• Abrahamsson, Niclas. 2012. Age of onset and nativelike L2 ultimate attainment of morphosyntactic and phonetic intuition. Studies in Second Language Acquisition 34: 187–214. [ Google Scholar ] [ CrossRef ]
• Andringa, Sible. 2014. The use of native speaker norms in critical period hypothesis research. Studies in Second Language Acquisition 36: 565–96. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Asher, James, and Ramiro García. 1969. The optimal age to learn a foreign language. Modern Language Journal 53: 334–41. [ Google Scholar ]
• Ayer, Alfred J. 1959. History of the Logical Positivist movement. In Logical Positivism . Edited by Alfred J. Ayer. New York: Free Press, pp. 3–28. [ Google Scholar ]
• Bates, Elizabeth, Donna Thal, Doris Trauner, Judi Fenson, Dorothy Aram, Julie Eisele, and Ruth Nass. 1997. From first words to grammar in children with focal brain injury. Developmental Neuropsychology 13: 275–343. [ Google Scholar ] [ CrossRef ]
• Baumert, Jürgen, Johanna Fleckenstein, Michael Leucht, Olaf Köller, and Jens Möller. 2020. The long-term proficiency of early, middle, and late starters learning English as a foreign language at school: A narrative review and empirical study. Language Learning 70: 1091–135. [ Google Scholar ] [ CrossRef ]
• Bergmann, Christopher, Nienke Meulman, Laurie Stowe, Simone Sprenger, and Monika Schmid. 2015. Prolonged L2 immersion engenders little change in morphosyntactic processing of bilingual natives. Neuroreport 26: 1065–70. [ Google Scholar ] [ CrossRef ]
• Birdsong, David, and Jan Vanhove. 2016. Age of second-language acquisition: Critical periods and social concerns. In Bilingualism across the Lifespan: Factors Moderating Language Proficiency . Edited by Elena Nicoladis and Simona Montanari. Berlin and Washington: De Gruyter Mouton/American Psychological Association, pp. 163–82. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Birdsong, David. 2008. Second language acquisition and ultimate attainment. In The Handbook of Applied Linguistics . New York: Wiley, pp. 82–105. [ Google Scholar ]
• Birdsong, David. 2014. The Critical Period Hypothesis for second language acquisition: Tailoring the coat of many colors. In Essential Topics in Applied Linguistics and Multilingualism . Edited by Mirosław Pawlak and Larissa Aronin. Heidelberg: Springer, pp. 43–50. [ Google Scholar ]
• Birdsong, David. 2017. Critical periods. In Oxford Bibliographies in Linguistics . Edited by Mark Aronoff. New York: Oxford University Press, Available online: https://www.oxfordbibliographies.com/view/document/obo-9780199772810/obo-9780199772810-0139.xml (accessed on 10 August 2021).
• Birdsong, David. 2018. Plasticity, variability and age in second language acquisition and bilingualism. Frontiers in Psychology 9: 81. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Biro, Frank M., Bin Huang, Halley Wasserman, Catherine M. Gordon, and Susan M. Pinney. 2020. Pubertal growth, IGF-1, and windows of susceptibility: Puberty and future breast cancer risk. Journal of Adolescent Health 68: 517–22. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Bongaerts, Theo. 1999. Ultimate attainment in L2 pronunciation: The case of very advanced L2 learners. In Second Language Acquisition and the Critical Period Hypothesis . Edited by David Birdsong. Mahwah: Lawrence Erlbaum. [ Google Scholar ]
• Bongaerts, Theo. 2003. Effets de l’âge sur l’acquisition de la pronunciation d’une seconde langue. Acquisition et Interaction en Langue Étrangère 18: 79–98. [ Google Scholar ] [ CrossRef ]
• Bowden, Harriet Wood, Karsten Steinhauer, Cristina Sanz, and Michael T. Ullman. 2013. Native-like brain processing of syntax can be attained by university foreign language learners. Neuropsychologia 51: 2492–511. [ Google Scholar ] [ CrossRef ]
• Burstall, Clare. 1975. Primary French in the balance. Foreign Language Annals 10: 245–52. [ Google Scholar ] [ CrossRef ]
• Carroll, John B. 1975. The Teaching of French as a Foreign Language in Eight Countries . New York: Wiley. [ Google Scholar ]
• Carroll, John B. 1981. Twenty-five years of research on foreign language aptitude. In Individual Differences and Universals in Language Learning Aptitude . Edited by Karl C. Diller. Rowley: Newbury House, pp. 83–118. [ Google Scholar ]
• Chen, Tony, and Joshua K. Hartshorne. 2021. More evidence from over 1.1 million subjects that the critical period for syntax closes in late adolescence. Cognition 214: 104706. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Cisneros-Franco, J. Miguel, Patrice Voss, Maryse E. Thomas, and Etienne de Villers-Sidani. 2020. Critical periods of brain development. Handbook of Clinical Neurology 173: 75–88. [ Google Scholar ] [ CrossRef ]
• Clark, Herbert H., and Eve V. Clark. 1977. Psychology and Language: An Introduction to Psycholinguistics . New York: Harcourt Brace Jovanovich. [ Google Scholar ]
• Cook, Vivian. 2002. Background to the L2 user. In Portraits of the L2 User . Edited by Vivian Cook. Clevedon: Multilingual Matters, pp. 1–28. [ Google Scholar ]
• Cook, Vivian. 2016. Premises of multicompetence. In Cambridge Handbook of Linguistic Multi-Competence . Edited by Vivian Cook and Li Wei. Cambridge: Cambridge University Press, pp. 1–25. [ Google Scholar ]
• Dąbrowska, Ewa, Laura Becker, and Luca Miorelli. 2020. Is Adult Second Language Acquisition Defective? Frontiers in Psychology 11: 1839. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Dąbrowska, Ewa. 2012. Different speakers, different grammars: Individual differences in native language attainment. Linguistic Approaches to Bilingualism 2: 219–53. [ Google Scholar ] [ CrossRef ]
• Davies, Alan. 2003. The Native Speaker: Myth and Reality . Clevedon: Multilingual Matters. [ Google Scholar ]
• Davies, Alan. 2004. The native speaker in applied linguistics. In The Handbook of Applied Linguistics . Edited by Alan Davies and Catherine Elder. Malden: Blackwell, pp. 431–50. [ Google Scholar ]
• DeKeyser, Robert. 2000. The robustness of critical period effects in second language acquisition. Studies in Second Language Acquisition 22: 499–533. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• DeKeyser, Robert. 2003. Implicit and explicit learning. In Handbook of Second Language Acquisition . Edited by Catherine J. Doughty and Michael H. Long. London: Blackwell, pp. 313–48. [ Google Scholar ]
• DeLuca, Vincent, David Miller, Christos Pliatsikas, and Jason Rothman. 2019. Brain Adaptations and Neurological Indices of Processing in Adult Second Language Acquisition. In The Handbook of the Neuroscience of Multilingualism . New York: John Wiley & Sons, Ltd., pp. 170–96. [ Google Scholar ] [ CrossRef ]
• Dewaele, Jean-Marc, Thomas Bak, and Lourdes Ortega. In press. Why the mythical ‘native speaker’ has mud on its face. In Changing Face of the “Native Speaker”: Perspectives from Multilingualism and Globalization . Edited by Nikolay Slavkov, Sílvia Melo Pfeifer and Nadja Kerschhofer-Puhalo. Berlin: Mouton De Gruyter.
• Dollmann, Jörg, Irena Kogan, and Markus Weißmann. 2020. Speaking Accent-Free in L2 Beyond the Critical Period: The Compensatory Role of Individual Abilities and Opportunity Structures. Applied Linguistics 41: 787–809. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Eisenstein, Miriam. 1980. Childhood bilingualism and adult language learning aptitude. International Review of Applied Psychology 29: 159–74. [ Google Scholar ] [ CrossRef ]
• Ellis, Nick C. 2017. Chunking in language usage, learning and change: I don’t know. In The Changing English Language: Psycholinguistic Perspectives . Edited by Marianne Hundt, Sandra Mollin and Simone E. Pfenninger. Cambridge: Cambridge University Press, pp. 113–47. [ Google Scholar ]
• Flege, James E. 2019. A Non-critical Period for Second-language Learning. In A Sound Approach to Language Matters—In Honor of Ocke-Schwen Bohn . Edited by Anne Mette Nyvad, Michaela Hejná, Anders Højen, Anna Bothe Jespersen and Mette Hjortshøj Sørensen. Aarhus: Aarhus University, pp. 501–41. [ Google Scholar ]
• Flege, James Emil, and Ocke-Schwen Bohn. 2021. The Revised Speech Learning Model (SLM-r). In Second Language Speech Learning: Theoretical and Empirical Progress . Edited by Ratree Wayland. Cambridge: Cambridge University Press, pp. 3–83. [ Google Scholar ] [ CrossRef ]
• Flege, James Emil, Grace H. Yeni-Komshian, and Serena Liu. 1999. Age constraints on second-language acquisition. Journal of Memory and Language 41: 78–104. [ Google Scholar ] [ CrossRef ]
• Frank, Michael C. 2018. With Great Data Comes Great (Theoretical) Opportunity. Trends in Cognitive Sciences 22: 669–71. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Granena, Gisela, and Michael H. Long. 2013. Age of onset, length of residence, language aptitude, and ultimate L2 attainment in three linguistic domains. Second Language Research 29: 311–43. [ Google Scholar ] [ CrossRef ]
• Hartshorne, Joshua K., Joshua B. Tenenbaum, and Steven Pinker. 2018. A critical period for second language acquisition: Evidence from 2/3 million English speakers. Cognition 177: 263–77. [ Google Scholar ] [ CrossRef ]
• Hoey, Michael. 2007. Grammatical creativity: A corpus perspective. In Text, Discourse and Corpora: Theory and Analysis . Edited by Michael Hoey, Michaela Mahlberg, Michael Stubbs and Wolfgang Teubert. London: Continuum, pp. 31–56. [ Google Scholar ]
• Huang, Becky H. 2016. A synthesis of empirical research on the linguistic outcomes of early foreign language instruction. International Journal of Multilingualism 13: 257–73. [ Google Scholar ] [ CrossRef ]
• Huang, Becky, Yung-Hsiang Shawn Chang, Luping Niu, and Mingxia Zhi. 2018. Examining the effects of socio-economic status and language input on adolescent English learners’ speech production outcomes. System 73: 27–36. [ Google Scholar ] [ CrossRef ]
• Hulstijn, Jan H. 2019. An individual-differences framework for comparing nonnative with native speakers: Perspectives from BLC theory. Language Learning 69: 157–83. [ Google Scholar ] [ CrossRef ]
• Huttenlocher, Janellen, Heidi Waterfall, Marina Vasilyeva, Jack Vevea, and Larry V. Hedges. 2010. Sources of variability in children’s language growth. Cognitive Psychology 61: 343–65. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Hyltenstam, Kenneth, and Niclas Abrahamsson. 2003. Maturational constraints in SLA. In The Handbook of Second Language Acquisition . Edited by Catherine Doughty and Michael H. Long. Malden: Blackwell, pp. 539–88. [ Google Scholar ]
• Hyltenstam, Kenneth. 1992. Non-native features of near-native speakers: On the ultimate attainment of childhood L2 learners. Advances in Psychology 83: 351–68. [ Google Scholar ]
• Jarvis, Scott, and Aneta Pavlenko. 2008. Crosslinguistic Influence in Language and Cognition . London: Routledge. [ Google Scholar ]
• Johnson, Jacqueline S., and Elissa L. Newport. 1989. Critical period effects in second language learning: The influence of maturational state on the acquisition of English as a second language. Cognitive Psychology 21: 60–99. [ Google Scholar ] [ CrossRef ]
• Kasparian, Kristina, and Karsten Steinhauer. 2016. Confusing similar words: ERP correlates of lexical-semantic processing in first language attrition and late second language acquisition. Neuropsychologia 93: 200–17. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Kasparian, Kristina, and Karsten Steinhauer. 2017. When the Second Language Takes the Lead: Neurocognitive Processing Changes in the First Language of Adult Attriters. Frontiers in Psychology 8: 389. [ Google Scholar ] [ CrossRef ] [ PubMed ] [ Green Version ]
• Kinsella, Ciara, and David Singleton. 2014. Much more than age. Applied Linguistics 35: 441–62. [ Google Scholar ] [ CrossRef ]
• Knudsen, Eric. 2004. Sensitive periods in the development of the brain and behavior. Journal of Cognitive Neuroscience 16: 1412–25. [ Google Scholar ] [ CrossRef ]
• Kormos, Judit. 2013. New conceptualizations of language aptitude in second language attainment. In Sensitive Periods, Language Aptitude and Ultimate Attainment . Edited by Gisela Granena and Mike Long. Amsterdam: John Benjamins, pp. 131–52. [ Google Scholar ]
• Kral, Andrej, and Jos J. Eggermont. 2007. What’s to lose and what’s to learn: Development under auditory deprivation, cochlear implants and limits of cortical plasticity. Brain Research Reviews 56: 259–69. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Krashen, Stephen. 1973. Lateralization, language learning and the critical period: Some new evidence. Language Learning 23: 63–74. [ Google Scholar ] [ CrossRef ]
• Lantolf, James P., and Steven L. Thorne. 2006. Sociocultural Theory and the Genesis of Second Language Development . Oxford: Oxford University Press. [ Google Scholar ]
• Lenneberg, Eric H. 1967. Biological Foundations of Language . New York: Wiley. [ Google Scholar ]
• Long, Michael H. 1990. Maturational constraints on language development. Studies in Second Language Acquisition 12: 251–85. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Long, Michael H. 1993. Second language acquisition as a function of age. In Progression and Regression in Language: Sociocultural, Neuropsychological and Linguistic Perspectives . Edited by Kenneth Hyltenstam and Ake Viberg. Cambridge: Cambridge University Press, pp. 196–221. [ Google Scholar ]
• Long, Michael. 2013. Maturational constraints on child and adult SLA. In Sensitive Periods, Language Aptitude and Ultimate Attainment . Edited by Gisela Granena and Michael Long. Amsterdam: John Benjamins, pp. 3–41. [ Google Scholar ]
• Marinova-Todd, Stefka H., D. Bradford Marshall, and Catherine E. Snow. 2000. Three misconceptions about age and L2 learning. TESOL Quarterly 34: 9–34. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Meisel, Jürgen M. 2008. Child second language acquisition or successive first language acquisition? In Current Trends in Child Second Language Acquisition. A Generative Perspective . Edited by Belma Haznedar and Elena Gavruseva. Amsterdam: John Benjamins, pp. 55–80. [ Google Scholar ]
• Meisel, Jürgen M. 2010. Age of onset in successive acquisition of bilingualism: Effects on grammatical development. In Language Acquisition across Linguistic and Cognitive Systems . Edited by Michèle Kail and Maya Hickmann. Amsterdam: John Benjamins, pp. 225–48. [ Google Scholar ]
• Moyer, Alene. 1999. Ultimate attainment in L2 phonology: The critical factors of age, motivation and instruction. Studies in Second Language Acquisition 21: 81–108. [ Google Scholar ] [ CrossRef ]
• Moyer, Alene. 2004. Age, Accent and Experience in Second Language Acquisition. An Integrated Approach to Critical Period Inquiry . Clevedon: Multilingual Matters. [ Google Scholar ]
• Moyer, Alene. 2013. Foreign Accent. The Phenomenon of Non-Native Speech . Cambridge: Cambridge University Press. [ Google Scholar ]
• Moyer, Alene. 2014. What’s age got to do with it? Accounting for individual factors in second language accent. Studies in Second Language Learning and Teaching 4: 443–64. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Muñoz, Carmen, and David Singleton. 2011. A critical review of age-related research on L2 ultimate attainment’. Language Teaching 44: 1–35. [ Google Scholar ] [ CrossRef ]
• Murphy, Victoria A. 2014. Second Language Learning in the Early School Years: Trends and Contexts . Oxford: Oxford University Press. [ Google Scholar ]
• Nenert, Rodolphe, Jane B. Allendorfer, Amber M. Martin, Christi Banks, Jennifer Vannest, Scott K. Holland, and Jerzy P. Szaflarski. 2017. Age-related language lateralization assessed by fMRI: The effects of sex and handedness. Brain Research 1674: 20–35. [ Google Scholar ] [ CrossRef ]
• Nijakowska, Joanna. 2010. Dyslexia in the Foreign Language Classroom . Bristol: Multilingual Matters. [ Google Scholar ]
• Patkowski, Mark S. 1980. The sensitive period for the acquisition of syntax in a second language. Language Learning 30: 449–68. [ Google Scholar ] [ CrossRef ]
• Penfield, Wilder, and Lamar Roberts. 1959. Speech and Brain Mechanisms . Princeton: Princeton University Press. [ Google Scholar ]
• Pfenninger, Simone E., and David Singleton. 2017. Beyond Age Effects in Instructional L2 Learning: Revisiting the Age Factor . Bristol: Multilingual Matters. [ Google Scholar ]
• Piske, Thorsten, James Emil Flege, Ian R. A. MacKay, and Diane Meador. 2002. The production of English vowels by fluent early and late Italian-English bilinguals. Phonetica 59: 49–71. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Pliatsikas, Christos, Elisavet Moschopoulou, and James Douglas Saddy. 2015. The effects of bilingualism on the white matter structure of the brain. Proceedings of the National Academy of Sciences of the United States of America 112: 1334–37. [ Google Scholar ] [ CrossRef ] [ PubMed ] [ Green Version ]
• Popper, Karl. 1959. The Logic of Scientific Discovery . New York: Basic Books. [ Google Scholar ]
• Purves, Dale, George Augustine, David Fitzpatrick, Willliam C. Hall, Anthony-Samuel LaMantia, James O. McNamara, and S. Mark Williams, eds. 2004. Neuroscience , 3rd ed. Sunderland: Sinauer. [ Google Scholar ]
• Roberts, Celia. 2013. Early puberty, ‘sexualization’ and feminism. European Journal of Women’s Studies 20: 138–54. [ Google Scholar ] [ CrossRef ]
• Robinson, Peter, ed. 2002. Individual Differences and Instructed Language Learning . Amsterdam: John Benjamins. [ Google Scholar ]
• Rosenthal, Judith W. 1996. Teaching Science to Language Minority Students: Theory and Practice . Clevedon: Multilingual Matters. [ Google Scholar ]
• Rossi, Eleonora, Judith F. Kroll, and Paola E. Dussias. 2014. Clitic pronouns reveal the time course of processing gender and number in a second language. Neuropsychologia 62: 11–25. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Rossi, Eleonora, Michele Diaz, Judith F. Kroll, and Paola E. Dussias. 2017. Late bilinguals are sensitive to unique aspects of second language processing: Evidence from clitic pronouns word-order. Frontiers in Psychology 8: 342. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Ruben, Robert J. 1997. A time frame of critical/sensitive periods of language development. Acta Otolaryngologica 117: 202–5. [ Google Scholar ] [ CrossRef ] [ PubMed ] [ Green Version ]
• Sáfár, Anna, and Judit Kormos. 2008. Revisiting problems with foreign language aptitude. International Review of Applied Linguistics in Language Teaching 46: 113–36. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Seliger, Herbert, Stephen Krashen, and Peter Ladefoged. 1975. Maturational constraints in the acquisition of second language accent. Language Sciences 36: 20–22. [ Google Scholar ]
• Sinclair, John. 1991. Corpus, Concordance, Collocation . Oxford: Oxford University Press. [ Google Scholar ]
• Singleton, David, and Justyna Leśniewska. 2021. Phraseology: Where lexicon and syntax conjoin. Research in Language and Education: An International Journal [RILE] 1: 46–58. [ Google Scholar ]
• Singleton, David, and Simone E. Pfenninger. 2016. Reporting on politically sensitive issues: The case of telling the truth about early L2 instruction. In Doing Real Research in Applied Linguistics . Edited by Jim McKinley and Heath Rose. London: Routledge, pp. 214–24. [ Google Scholar ]
• Singleton, David. 2005. The Critical Period Hypothesis: A coat of many colours. International Review of Applied Linguistics 43: 269–85. [ Google Scholar ] [ CrossRef ]
• Singleton, David. 2017. Language aptitude: Desirable trait or acquirable attribute? Studies in Second Language Learning and Teaching 7: 89–103. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Singleton, David. 2020a. Grammatical questions: Phraseological answers. In Text-Sentence-Word: Studies in English Linguistics, vol. IV . Edited by Agnieszka Uberman and Magdalena Trinder. Rzeszów: Wydawnictwo Uniwersytetu Rzeszowskiego. [ Google Scholar ]
• Singleton, David. 2020b. The translanguaging conundrum. In Bilingualism: Hungarian and Non-Hungarian Contexts . Edited by Szilvia Bátyi, Maria Gósy, Pal Heltai, Zsolt Lengyel and Szilard Szentgyörgy. Veszprém: Pannon Egyetem, pp. 175–84. [ Google Scholar ]
• Singleton, David. 2021. Postface. In Perspectives on the Second Language Phrasicon—The View from Learner Corpora . Edited by Sylviane Granger. Bristol: Multilingual Matters, pp. 235–44. [ Google Scholar ]
• Sparks, Richard L., Leonore Ganschow, Kay Fluharty, and Sherwin Little. 1995. An exploratory study on the effects of Latin on the native language skills and foreign language aptitude of students with and without learning disabilities. The Classical Journal 91: 165–84. [ Google Scholar ]
• Steinhauer, Karsten, and Kristina Kasparian. 2020. Brain plasticity in adulthood—ERP evidence for L1-attrition in lexicon and morphosyntax after predominant L2 use. Language Learning 70: 171–93. [ Google Scholar ] [ CrossRef ]
• Swain, Merrill, and Sharon Lapkin. 1989. Aspects of the sociolinguistic performance of early and late French immersion students. In Developing Communicative Competence in a Second Language . Edited by Robin C. Scarcella, Elaine S. Andersen and Stephen D. Krashen. Cambridge: Newbury House, pp. 41–54. [ Google Scholar ]
• Thorpe, William H. 1954. The process of song-learning in the chaffinch as studied by means of the sound spectrograph. Nature 173: 465–69. [ Google Scholar ] [ CrossRef ]
• Turnbull, Miles, Sharon Lapkin, Doug Hart, and Merrill Swain. 1998. Time on task and immersion graduates’ French proficiency. In French Second Language Education in Canada: Empirical Studies . Edited by Sharon Lapkin. Toronto: University of Toronto Press, pp. 31–55. [ Google Scholar ]
• Vanhove, Jan. 2013. The Critical Period Hypothesis in Second Language Acquisition: A Statistical Critique and a Reanalysis. PLoS ONE 8: e69172. [ Google Scholar ] [ CrossRef ] [ Green Version ]
• Vasilyeva, Marina, Heidi Waterfall, and Janellen Huttenlocher. 2008. Emergence of syntax: Commonalities and differences across children. Developmental Science 11: 84–97. [ Google Scholar ] [ CrossRef ] [ PubMed ]
• Wei, Li. 2018. Translanguaging as a practical theory of language. Applied Linguistics 39: 9–30. [ Google Scholar ] [ CrossRef ] [ Green Version ]

Share and Cite

Singleton, D.; Leśniewska, J. The Critical Period Hypothesis for L2 Acquisition: An Unfalsifiable Embarrassment? Languages 2021 , 6 , 149. https://doi.org/10.3390/languages6030149

Singleton D, Leśniewska J. The Critical Period Hypothesis for L2 Acquisition: An Unfalsifiable Embarrassment? Languages . 2021; 6(3):149. https://doi.org/10.3390/languages6030149

Singleton, David, and Justyna Leśniewska. 2021. "The Critical Period Hypothesis for L2 Acquisition: An Unfalsifiable Embarrassment?" Languages 6, no. 3: 149. https://doi.org/10.3390/languages6030149

Article Metrics

Article access statistics, further information, mdpi initiatives, follow mdpi.

Subscribe to receive issue release notifications and newsletters from MDPI journals

Academia.edu no longer supports Internet Explorer.

To browse Academia.edu and the wider internet faster and more securely, please take a few seconds to  upgrade your browser .

Enter the email address you signed up with and we'll email you a reset link.

• We're Hiring!
• Help Center

The Critical Period Hypothesis in Second Language Acquisition: A Review of the Literature

Related Papers

Niclas Abrahamsson , Kenneth Hyltenstam

Results from a number of recent studies suggest that nativelike adult second language (L2) learners possess a high degree of language learning aptitude, the positive effects of which may have compensated for the negative effects of a critical period in these learners. According to the same studies, child learners seem to attain a native-like command of the L2 regardless of high or low aptitude, which has led researchers to conclude that this factor plays no role in early acquisition. The present study investigates the L2 proficiency and language aptitude of 42 near-native L2 speakers of Swedish (i.e., individuals whom actual mother-tongue speakers of Swedish believe are native speakers). The results confirm previous research suggesting that a high degree of language aptitude is required if adult learners are to reach a L2 proficiency that is indistinguishable from that of native speakers. However, in contrast to previous studies, the present results also identify small yet significant aptitude effects in child SLA. Our findings lead us to the conclusions that the rare nativelike adult learners sometimes observed would all turn out to be exceptionally talented language learners with an unusual ability to compensate for maturational effects and, consequently, that their nativelikeness per se does not constitute a reason to reject the critical period hypothesis.

The incidence of nativelikeness in adult second language acquisition is a controversial issue in SLA research. Although some researchers claim that any learner, regardless of age of acquisition, can attain nativelike levels of second language (L2) proficiency, others hold that attainment of nativelike proficiency is, in principle, impossible. The discussion has traditionally been framed within the paradigm of a critical period for language acquisition and guided by the question of whether SLA is constrained by the maturation of the brain. The work presented in this article can be positioned among those studies that have focused exclusively on the apparent counterexamples to the critical period. We report on a large-scale study of Spanish/Swedish bilinguals (n = 195) with differing ages of onset of acquisition (<1–47 years), all of whom identify themselves as potentially nativelike in their L2. Listening sessions with native-speaker judges showed that only a small minority of those bilinguals who had started their L2 acquisition after age 12, but a majority of those with an age of onset below this age, were actually perceived as native speakers of Swedish. However, when a subset (n = 41) of those participants who did pass for native speakers was scrutinized in linguistic detail with a battery of 10 highly complex, cognitively demanding tasks and detailed measurements of linguistic performance, representation, and processing, none of the late learners performed within the native-speaker range; in fact, the results revealed also that only a few of the early learners exhibited actual nativelike competence and behavior on all measures of L2 proficiency that were employed. Our primary interpretation of the results is that nativelike ultimate attainment of a second language is, in principle, never attained by adult learners and, furthermore, is much less common among child learners than has previously been assumed.

Language Teaching

Carmen Munoz

Niclas Abrahamsson

Research has consistently shown there is a negative correlation between age of onset (AO) of acquisition and ultimate attainment (UA) of either pronunciation or grammar in a second language (L2). A few studies have indeed reported nativelike behavior in some postpuberty learners with respect to either phonetics/phonology or morphosyntax, a result that has sometimes been taken as evidence against the critical period hypothesis (CPH). However, in the few studies that have employed a wide range of linguistic tests and tasks, adult learners have not exhibited nativelike L2 proficiency across the board of measures, which, according to some, suggests that the hypothesis still holds. The present study investigated the relationship between AO and UA and the incidence of nativelikeness when measures of phonetic and grammatical intuition are combined. An additional aim was to investigate whether children and adults develop the L2 through fundamentally different brain mechanisms—namely, whether children acquire the language (more) implicitly as an interdependent whole, whereas adults learn it (more) explicitly as independent parts of a whole.

Sible Andringa

In critical period hypothesis (CPH) research, native speaker (NS) norm groups have often been used to determine whether nonnative speakers (NNSs) were able to score within the NS range of scores. One goal of this article is to investigate what NS samples were used in previous CPH research. The literature review shows that NS control groups tend to be small and highly educated and that detailed background information is usually not provided. Another goal of this article is to investigate how the NS norm group may affect the incidence of nativelike performance by NNSs. To this end, 124 NSs and 118 NNSs of Dutch completed five comprehension tasks and a vocabulary task. On the basis of mean scores and standard deviations, norms were determined for a representative and a nonrepresentative (highly educated) subsample of NSs. Also, separate norms were constructed for the high- and low-frequency items within a task. Exact McNemar tests were used to establish that the incidence of nativelike performance by NNSs was significantly higher if a representative sample norm was used. The results also showed that, insofar as there were effects of frequency, norms based on low-frequency test items tended to be more inclusive. The results imply that the selection of NSs in CPH research deserves more consideration than it has received in the past; they also suggest that NS ceiling performance is potentially useful in determining nativelike performance.

Clara Burgo

Language. In K. Knapp & B. Seidlhofer (eds.), Handbook of Foreign Communication and Learning. Berlin: Mouton De Gruyter, pp. 279-306.

Jean-Marc Dewaele

TESOL Quarterly

Kenneth Hyltenstam

Loading Preview

Sorry, preview is currently unavailable. You can download the paper by clicking the button above.

RELATED PAPERS

Koki Shimazu

Andrea Hellman

Huynh Mimh Thu

Revista Todas as Letras

Melissa Bettoni

Studies in Second Language Acquisition

Roumyana Slabakova

e-spacio.uned.es

Jorge G Berges-Puyó

Bilingualism-language and Cognition

Linguistic Approaches to Bilingualism

Isaac Rodriguez

Australian Journal of Learning Difficulties

Salim Abu-Rabia

Journal of Psycholinguistic Research

Becky H. Huang

IRAL - International Review of Applied Linguistics in Language Teaching

Marianne Nikolov

Francis Tejeda

Melike Ünal Gezer , Burgess- Brigham , Jung-Hsuan Su

Tanja Kupisch

G. Grañena & M. Long (eds.), Sensitive Periods, Language Aptitude, and Ultimate L2 Attainment. (pp. 69-102).

Edbert Quebral

Applied Linguistics

Nashid Nigar

Ale L , Tej Bhatia

Talal Alghizzi

Mind and context in adult second language acquisition

Cristina Sanz

… Language and Cognition

john betancourth

Simone Pfenninger , David Singleton

Language Learning, 65,3

Olli Aaltonen , Melike Uzal

Janet Beilman

Mario Ruiz Moreno

SYAHRIR Ongkang

Learning and Individual Differences

Victor Van Daal

Language Learning

Alex Fine , T. Florian Jaeger

Dony Marzuki

Blackwell Handbook of Advanced Proficiency

John Archibald

•   We're Hiring!
•   Help Center
• Find new research papers in:
• Health Sciences
• Earth Sciences
• Cognitive Science
• Mathematics
• Computer Science
• Academia ©2024

Stack Exchange Network

Stack Exchange network consists of 183 Q&A communities including Stack Overflow , the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Q&A for work

Connect and share knowledge within a single location that is structured and easy to search.

What are the main arguments for and against the critical period hypothesis, and what are alternative explanations?

Why is the critical period hypothesis so heavily disputed, yet widely accepted; what are its major strengths and weaknesses; what other explanations exist for the perceived "critical period", if it does not exist?

• critical-period

Let us start with a simple, relatively informal statement: “in most cases, those who start learning a language as children become ultimately become more proficient in a language than those who start learning it later”. This is uncontroversial, and something I think the vast majority of second-language acquisition researchers would agree on. However, this is not how the Critical Period Hypothesis (CPH) is understood within the field of Second Language Acquisition (SLA). CPH is a large subject, and your question is hard to answer in a few paragraphs. Therefore, I am reusing large fragments of an assignment I wrote on this very topic for an SLA course a few years ago. Let me know if something is unclear or the style is too terse at some points.

Summary (TL;DR)

There is no universally accepted definition of a critical period within linguistics and some of the controversies are caused by the fact that different researchers use different definitions.

There are a few key findings that are not controversial:

• early learners perform consistently well in all aspects of language use,
• as we move the starting age, they perform statistically worse and worse until puberty,
• however, the decrease in performance is not uniform.

An explanation, provided by Bialystok (1997) as an alternative to CPH, is the different learning style of children, compared to late learners.

Paradoxically, the differences (or lack thereof) between those who learn a foreign language as adults is the key factor in deciding whether CPH is true or not, and a controversial one:

• Some studies found correlations between the age adult learners started learning a language and their ultimate attainment. In other words, these studies suggest that if we compare people who have been learning a language for a very long time, the ultimate attainment of those who started at the age of 20 is statistically higher than the ultimate attainment of those who started at the age of 40. These studies argue that there is no CPH in the childhood, but rather that our abilities in learning a new language consistently decrease throughout our whole lives.
• Other studies found no clear correlations between the starting age and the ultimate attainment among adult language learners. They point out that the correlation between the starting age and ultimate attainment is clear for those who started before puberty. Based on that, they argue that there is something qualitatively different about starting to learn in an early age, and therefore conclude that it is an argument for CPH.

Definitions of the critical period used by those who argue against CPH

Controversies with the Critical Period Hypothesis (CPH) are related to the issue of ultimate attainment of early and late language learners, that is, the highest language proficiency level they can attain. The patterns in ultimate attainment may be explained by CPH, but they may also have different explanations. Some researchers support some form of the Critical Period Hypothesis (Johnson and Newport 1989, DeKeyser and Larson-Hall 2005, Patkowsky 1994, Scovel 1988), while others argue against it (Bialystok 1997).

A major problem with the Critical Period Hypothesis is that there appears to be no universally accepted definition of a critical period within linguistics . Bialystok (1997) bases her discussion of the critical/sensitive period (which she takes to be synonymous 1 ) on a specific technical definition used in ethology, which includes 14 essential structural characteristics that describe such a period (Bornstein 1989). She argues that one of these characteristics is especially problematic – the system: “structure or function altered in the sensitive period” (Bornstein 1989:184). In other words, she argues that there is no period where a structure in the brain is modified in a way that makes subsequent language learning harder or impossible. Bialystok does, however, agree that there is an optimal period for language learning – something that can be characterised by the statement “ On average, children are more successful than adults when faced with the task of learning a second language ” (Bialystok 1997:117). Despite the controversy around other issues, this fact is uncontested and has been verified by numerous studies .

Bialystok (1997) rejects the existence of a critical period, because of lack of postulated structure that is modified when the period is over. She postulates that an important factor that causes differences in ultimate attainment between early and late starters is learning style: children prefer accommodation (creating new concepts) over assimilation (extending existing concepts). The question remains: why do they prefer accommodation? She suggests that “[t]his may be because children are in the process of creating new categories all the time as they are learning new information” (Bialystok 1997:132).

Definitions of the critical period used by supporters of CPH

The researchers who support some form of the Critical Period Hypothesis (Johnson and Newport 1989, DeKeyser and Larson-Hall 2005), formulate it in a form that is much weaker than Bialystok's (1997) formulation. What they postulate often resembles what Bialystok calls the optimal age.

Johnson and Newport (1989) reformulated CPH into two alternative hypotheses, in order to fit second language acquisition into the picture:

The exercise hypothesis : “Early in life, humans have a superior capacity for acquiring languages. If the capacity is not exercised during this time, it will disappear or decline with maturation. If the capacity is exercised, however, further language learning abilities will remain intact throughout life.” (Johnson and Newport 1989:64)

The maturational state hypothesis : “Early in life, humans have a superior capacity for acquiring languages. This capacity disappears or declines with maturation.” (Johnson and Newport 1989:64)

We can see that if a critical period was found for second language acquisition, we could be almost sure that it exists for L1 acquisition as well (the maturational state hypothesis). However, we cannot deduce in this way in case of the exercise hypothesis – non-existence of a critical period for L2 acquisition does not exclude in any way a possibility of such period for the first language (Bialystok 1997).

DeKeyser and Larson-Hall (2005) formulate the hypothesis as: “language acquisition from mere exposure (i.e. implicit learning) […] is severely limited in older adolescents and adults”. Their formulation is quite vague, as is the constatation that there is a “qualitative change in language learning capacities somewhere between 4 and 18 years”.

There are also definitions that restrict the Critical Period Hypothesis to specific subareas of the language faculty. The most commonly mentioned area is phonology, see e.g. Patkowsky (1994, cited in Bialystok 1997), Scovel (1988, cited in Bialystok 1997).

Age effects before and after puberty

The current consensus is that early learners perform consistently well in all aspects of language use. As we move the starting age, they perform statistically worse and worse until puberty. The decrease in performance is not uniform, and in some areas (such as phonology) it is particularly visible. Performance on the same level as early bilinguals is possible, but rare.

Probably the most controversial aspect is the performance of adult learners. After puberty there is much bigger variance in the performance, so data are more prone to different interpretations. The results obtained by Derwing and Munro (2013) suggest that comprehensibility and good accent are negatively correlated with the age of arrival, that is, the age when English language immersion started. Johnson and Newport (1989) found no correlation of starting age after puberty with ultimate language proficiency, while Bialystok (1997) re-analysed these data and found some negative correlation. A meta-analysis by DeKeyser and Larson-Hall (2005) downplays the role of post-adolescent correlations. As we can see, the jury is still out on this debate.

1 In neuroscience critical period and sensitive period are two separate concepts, see Knudsen (2004).

Bibliography

• Bialystok, E. 1997. The structure of age: in search of barriers to second language acquisition. Second Language Research 13(2): 116-137.
• Bornstein, M.H. 1989. Sensitive periods in development: structural characteristics and causal interpretations. Psychological Bulletin 105,179–97.
• DeKeyser, R. and J. Larson-Hall. 2005. What does the critical period really mean? In J. F. Kroll and A. M. B. de Groot. 2005. Handbook of bilingualism: Psycholinguistic approaches . Cary, NC: Oxford University Press. Pp. 109–27.
• Derwing, T. M., & Munro, M. J. 2013. The development of L2 oral language skills in two L1 groups: A 7-year study. Language Learning 63, 163-185.
• Johnson, J.S., & Newport, E.L. 1989. Critical period effects in second language learning: The influence of maturational state on the acquisition of English as a second language. Cognitive Psychology , 21, 60-99.
• Knudsen, E. I. 2004. Sensitive periods in the development of the brain and behavior. Journal of Cognitive Neuroscience , 16, 1412-25
• Newport, E. L., & Supalla, T. 1987. A critical period effect in the acquisition of a primary language .
• Patkowsky, M. 1980. The sensitive period for the acquisition of syntax in a second language. Language Learning 30, 449–72
• Scovel, T. 1988. A time to speak: a psycholinguistic inquiry into the critical period for human speech . New York: Newbury House

Your Answer

Sign up or log in, post as a guest.

Required, but never shown

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy .

Not the answer you're looking for? Browse other questions tagged critical-period or ask your own question .

• Featured on Meta
• Upcoming initiatives on Stack Overflow and across the Stack Exchange network...
• We spent a sprint addressing your requests — here’s how it went

Hot Network Questions

• Reversing vowels in a string
• Did any 8-bit machine select palette by character name instead of color memory?
• What is the purpose of the BJT in this circuit?
• When do you know things are actually going poorly in graduate school?
• Cliffhanger ending?
• Strange Interaction with Professor
• Explain why "Calf" is the answer to "Ice mass broken off a little lower?"
• Making a node in TikZ occupy the vertical space of one line - at least as far as positioning a "pin" is concerned
• Old SF story about someone who detonated an atomic bomb, sacrificing self to save society from an evil government
• Are all Starship/Super Heavy "cylinders" 4mm thick?
• Error handling for singly linked list in C
• Greek myth about an athlete who kills another man with a discus
• Which of the following values can the expression NOT take?
• Why does `p` not put all yanked lines when copying across files?
• When Canadian citizen residing abroad comes to visit Canada
• Should "as a ..." and "unlike ..." clauses refer to the subject?
• How well does the following argument work as a counter towards unfalsifiable supernatural claims?
• Are there any parts of the US Constitution that state that the laws apply universally to all citizens?
• mirrorlist.centos.org no longer resolve?
• Is intuitionistic mathematics situated in time?
• Please explain the purpose of R3 and R4 in this ground isolating amplifier
• Sort Number Array
• Why danach instead of darüber?
• Concrete works by Alexandre Grothendieck, other than Dessin d'Enfants?

• Architecture and Design
• Asian and Pacific Studies
• Business and Economics
• Classical and Ancient Near Eastern Studies
• Computer Sciences
• Cultural Studies
• Engineering
• General Interest
• Geosciences
• Industrial Chemistry
• Islamic and Middle Eastern Studies
• Jewish Studies
• Library and Information Science, Book Studies
• Life Sciences
• Linguistics and Semiotics
• Literary Studies
• Materials Sciences
• Mathematics
• Social Sciences
• Sports and Recreation
• Theology and Religion
• Publish your article
• The role of authors
• Promoting your article
• Abstracting & indexing
• Publishing Ethics
• Why publish with De Gruyter
• How to publish with De Gruyter
• Our book series
• Our subject areas
• Your digital product at De Gruyter
• Contribute to our reference works
• Product information
• Tools & resources
• Product Information
• Promotional Materials
• Orders and Inquiries
• FAQ for Library Suppliers and Book Sellers
• Repository Policy
• Free access policy
• Open Access agreements
• Database portals
• For Authors
• Customer service
• People + Culture
• Journal Management
• How to join us
• Working at De Gruyter
• Mission & Vision
• De Gruyter Foundation
• De Gruyter Ebound
• Our Responsibility
• Partner publishers

Your purchase has been completed. Your documents are now available to view.

The Age Factor in Second Language Acquisition

• Edited by: David Singleton and Zsolt Lengyel
• X / Twitter

Please login or register with De Gruyter to order this product.

• Language: English
• Publisher: Multilingual Matters
• Copyright year: 1995
• Audience: College/higher education;
• Main content: 168
• Keywords: Language acquisition ; Language learning: specific skills
• Published: August 15, 1995
• ISBN: 9781800418240

An official website of the United States government

The .gov means it’s official. Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

The site is secure. The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

• Publications
• Account settings
• My Bibliography
• Collections
• Citation manager

Save citation to file

Email citation, add to collections.

• Create a new collection
• Add to an existing collection

Add to My Bibliography

Your saved search, create a file for external citation management software, your rss feed.

• Search in PubMed
• Search in NLM Catalog
• Add to Search

Critical evidence: a test of the critical-period hypothesis for second-language acquisition

Affiliation.

• 1 Stanford University, CA 94305, USA. [email protected]
• PMID: 12564751
• DOI: 10.1111/1467-9280.01415

The critical-period hypothesis for second-language acquisition was tested on data from the 1990 U.S. Census using responses from 2.3 million immigrants with Spanish or Chinese language backgrounds. The analyses tested a key prediction of the hypothesis, namely, that the line regressing second-language attainment on age of immigration would be markedly different on either side of the critical-age point. Predictions tested were that there would be a difference in slope, a difference in the mean while controlling for slope, or both. The results showed large linear effects for level of education and for age of immigration, but a negligible amount of additional variance was accounted for when the parameters for difference in slope and difference in means were estimated. Thus, the pattern of decline in second-language acquisition failed to produce the discontinuity that is an essential hallmark of a critical period.

PubMed Disclaimer

• Using census data to test the critical-period hypothesis for second-language acquisition. Stevens G. Stevens G. Psychol Sci. 2004 Mar;15(3):215-6. doi: 10.1111/j.0956-7976.2004.01503012.x. Psychol Sci. 2004. PMID: 15016295 No abstract available.

Similar articles

• How well do children who are internationally adopted acquire language? A meta-analysis. Scott KA, Roberts JA, Glennen S. Scott KA, et al. J Speech Lang Hear Res. 2011 Aug;54(4):1153-69. doi: 10.1044/1092-4388(2010/10-0075). Epub 2011 Feb 4. J Speech Lang Hear Res. 2011. PMID: 21297167 Review.
• The effects of late acquisition of L2 and the consequences of immigration on L1 for semantic and morpho-syntactic language aspects. Scherag A, Demuth L, Rösler F, Neville HJ, Röder B. Scherag A, et al. Cognition. 2004 Oct;93(3):B97-108. doi: 10.1016/j.cognition.2004.02.003. Cognition. 2004. PMID: 15178380 Clinical Trial.
• First-language acquisition in adolescence: evidence for a critical period for verbal language development. Grimshaw GM, Adelstein A, Bryden MP, MacKinnon GE. Grimshaw GM, et al. Brain Lang. 1998 Jun 15;63(2):237-55. doi: 10.1006/brln.1997.1943. Brain Lang. 1998. PMID: 9654433
• Critical period effects in second language learning: the influence of maturational state on the acquisition of English as a second language. Johnson JS, Newport EL. Johnson JS, et al. Cogn Psychol. 1989 Jan;21(1):60-99. doi: 10.1016/0010-0285(89)90003-0. Cogn Psychol. 1989. PMID: 2920538
• Hearing parents learning American Sign Language with their deaf children: a mixed-methods survey. Lieberman AM, Mitchiner J, Pontecorvo E. Lieberman AM, et al. Appl Linguist Rev. 2022 May 23;15(1):309-333. doi: 10.1515/applirev-2021-0120. eCollection 2024 Jan. Appl Linguist Rev. 2022. PMID: 38221976 Free PMC article.
• Language of instruction in schools in low- and middle-income countries: A systematic review. Nakamura P, Molotsky A, Zarzur RC, Ranjit V, Haddad Y, De Hoop T. Nakamura P, et al. Campbell Syst Rev. 2023 Oct 3;19(4):e1351. doi: 10.1002/cl2.1351. eCollection 2023 Dec. Campbell Syst Rev. 2023. PMID: 37795423 Free PMC article. Review.
• Home language and societal language skills in second-generation bilingual adults. Giguere D, Hoff E. Giguere D, et al. Int J Billing. 2020 Oct-Dec;24(5-6):1071-1087. doi: 10.1177/1367006920932221. Epub 2020 Jun 19. Int J Billing. 2020. PMID: 37465566 Free PMC article.
• The labor market outcomes of bilinguals in the United States: Accumulation and returns effects. Churkina O, Nazareno L, Zullo M. Churkina O, et al. PLoS One. 2023 Jun 29;18(6):e0287711. doi: 10.1371/journal.pone.0287711. eCollection 2023. PLoS One. 2023. PMID: 37384633 Free PMC article.
• Integration of visual context in early and late bilingual language processing: evidence from eye-tracking. Abashidze D, Schmidt A, Trofimovich P, Mercier J. Abashidze D, et al. Front Psychol. 2023 Apr 26;14:1113688. doi: 10.3389/fpsyg.2023.1113688. eCollection 2023. Front Psychol. 2023. PMID: 37179896 Free PMC article.

Publication types

• Search in MeSH

Related information

Linkout - more resources, full text sources.

• Ovid Technologies, Inc.

• Citation Manager

NCBI Literature Resources

MeSH PMC Bookshelf Disclaimer

The PubMed wordmark and PubMed logo are registered trademarks of the U.S. Department of Health and Human Services (HHS). Unauthorized use of these marks is strictly prohibited.