A critical period for language acquisition: let’s get critical

Ever heard that kids are naturals when it comes to learning a language? Or maybe you know someone who gets easily discouraged from attending a second language course because they say they’re too old. Whatever you might have heard about this, whether you can remember or not, I’m positive it’s related to one of the most famous linguistics debates, which has been around since the 1960s.

You see, this idea that there is a certain period of maximal language acquisition, and that it is essential to be exposed to language before this window closes, is still a matter of controversy.  But before we delve into the particularities of this debate, we must understand what language consists of, how we acquire or learn it, and, mainly, what this period might look like.

In the 1960s, the father of modern linguistics, Noam Chomsky (1965) proposed that humans must have some sort of internal mechanism, which he called the Language Acquisition Device (LAD), responsible for implicitly “picking up” language. Since babies are in a poor environment in terms of language stimuli (because parents oversimplify their language output) and still develop language quite automatically to fluency, this LAD must work regardless of the language being acquired. For that to be true, languages need to have generalizable grammatical rules and, thus, be formed by the same linguistic categories (such as verbs, nouns, adjectives, etc). This he called the Universal Grammar (UG).

Skinner (1957), on the other hand, had already proposed a theory to explain how humans acquire language through operant conditioning, specifically positive reinforcement. Basically, when a baby tries to say something and realizes that parents respond positively to that behavior and give them what they want, they do more and more of it.

Another theory is that babies “take statistics” of phonemes in their native language and start recognizing certain patterns that they use to acquire it (Kuhl et al. 2014).

Be it as it may, one thing is undeniable: humans have achieved an unparalleled level of complex language capable of expressing the most abstract thoughts like no other species. Teach a dog or a monkey as much as you want, but they will never learn language to the degree we have mastered it (some would argue they don’t even have language). Therefore, it is safe to assume that we learn language not only due to nature, but also nurture. And nature is what interests us now.

What might be some of the biological processes behind language acquisition? A very widely accepted, however still controversial, notion is that there is a maturational period for languages to develop. This is called the Critical Period Hypothesis (CPH) (Lenneberg, 1967).  Lenneberg popularized Penfield’s (1959) work and used its influences of animal experiments to suggest that, like many other biological systems and functions, language must be acquired before a certain age or it will be severely impaired. Hubel and Wiesel (1959) had already demonstrated that cats have around a 3-month window of opportunity to develop vision when adequately exposed to environmental stimuli (in this case, light). If they cannot open their eyes during this period, they will be virtually blind for the rest of their lives.

Based on this notion of a critical period, said to end at age 12 (Lenneberg, 1967), educators, policymakers, and parents around the globe can make very important decisions about language courses and children. However, how certain is science about this critical period? How can it be tested? What about people who have successfully learned a language after this period? Well, based on this ongoing linguistics debate, let’s try to answer some of these questions below:

1. Is language acquisition and language learning the same?

You might have noticed that at times I use the word acquisition and then learning. Krashen puts the difference quite simply: acquisition = more implicit, subconscious effort; learning = more explicit, conscious effort. According to a study done in Israel (Ferman & Karni, 2010), kids use more implicit mechanisms while adults use more explicit mechanism for language learning (or should I say acquisition?). Nevertheless, Ferman and Karni found no evidence that kids are better than young adults, they actually found the opposite.

2. How long does this critical period last?

Different authors have come to different conclusions. It could be anywhere between 5 and 18 years old. Nevertheless, one thing authors seem to agree on is that there might be different critical periods for different aspects of a language. Pronunciation, for instance, might have a critical period that ends before 1-year-old (Kuhl et al. 2014). It’s worth mentioning that a very large study was conducted by Hartshorne, Tenenbaum, and Pinker (2018) on almost 700 thousand people from all over the world and they believe our ability to learn a language starts declining after 17 yo. Now, whether this decline is exclusively maturational or due to a sudden loss of interest in language learning, substantial social life change, like going to university or work, remains unclear. Also, this large study didn’t test phonology.

3. Is it impossible (or nearly impossible) to learn a language after the critical period?

Again, there’s plenty of evidence out there supporting the fact that we can learn languages at any age. Some authors like Norrman and Bylund (1995) prefer to use the Montessorian notion of sensitive periods instead of critical because at the end of a critical period there should be a sharp decline in the acquisition of a function, which doesn’t seem to happen for language.

4. How can researchers test it?

It would be unethical to deprive kids of language exposure for many years and then do it to study if they’re still able to acquire this language. That’s why researchers look into second language acquisition as a proxy. However, studies with feral children (Curtiss, 1977) suggest that there is a critical period for first language acquisition. Genie was a 12yo girl found locked in a room who had never learned the written or spoken language. Her father constantly abused her and when a psychologist and linguist tried to teach her English, which would be her first language, she was unable to master it, using an excessively fragmented language filled with grammatical errors. The question is: was that because she had passed the critical period or a consequence of psychological trauma?

5. What are some of the possible gaps in Second Language Acquisition research?

Many studies don’t analyze the four abilities in language that we know based on the Common European Framework of Reference for Languages (CEFR). Most of the seminal studies focused on multiple-choice grammar-reading tests and disregarded oral fluency for instance. Another issue is that these studies normally create their own language tests and don’t use any official guideline necessarily. Of course, we must take into account that there is probably a linguist on the research team or that they referred to Johnson and Newport (1989)’s grammar test, however, one could argue that the lack of standardization is exactly of makes the results so divergent.

6. What about technology? Can it help end this debate?

Some neuroimaging studies (Andrews et al. 2013, Abutalebi, 2008) have suggested that the age of acquisition is not as important as the duration of exposure or proficiency levels. Early brain scans showed very distinct activations in the brain when the subjects used L1 versus when they used L2. However, these studies tested, for the most part, subjects that were not fluent. When advanced subjects were tested in a Functional Magnetic Resonance Imaging machine (fMRI), they were able to demonstrate that both L1 and L2 use very similar neuronal networks (same areas are activated) suggesting that the ultimate attainment (fluency level) of a second language can be quite similar to L1 and, thus, depend more on level of proficiency. Nonetheless, we cannot make bold claims and say that the debate is over.

7. Is it truly harder for adults to learn a second language when compared to kids and teens?

As language teachers, we might feel like jumping to that conclusion. But we must ask ourselves: how long does it take a kid to get to the C2 level? Is it faster than an adult learner? To me, it’s quite clear that adults can learn quite quickly at the beginning (faster than kids), especially if you think of how much vocabulary and grammar they can take in throughout a semester. But kids and teens might have a couple of advantages: 1) more exposure to L2 outside the classroom; 2) less interference of L1 on L2; 3) less fear of exposure in class; 4) less say in whether they will study an L2 or not (they don’t usually have a choice). Learners who started before the end of the critical period (as kids or teens) also seem to have more native-like pronunciation. The question is: which native?


Whether there is a critical period (or several) for language acquisition or not will remain a matter of debate for some time. What research knows for a fact is that there is compelling evidence for a decline in the ability to learn languages after a certain period of our lives. This decline may have biological reasons, no doubt, but it might also be related to social aspects or, the way I see it, both. Language is a social construct and it does not depend solely on the exposure to environmental stimuli. It requires social interaction, implicit and explicit efforts, reflection and persistence. We must also look at the other side of this story and see how many successful learners are out there who started learning a language in their 30s, 40s, 50s or older.

If there’s any disadvantage to starting a second language after what might be a critical period I’d say it’s not acquiring a native-like pronunciation. The thing is, I don’t think having a native-like pronunciation is such a big deal. Some native speakers of English have accents that might be easier or harder to understand and life goes on. I think we should embrace diversity and sound intelligible enough so that we can communicate with people.

I suppose my final message here is: don’t make this critical period hypothesis become a self-fulfilling prophecy. Not starting a second language course because you believe you’re way past the time to actually learn it is probably the biggest reason why will never learn it. Don’t take it from me, though, take it from 92yo Mary Hobson, who started studying Russian at 56 because of her passion for the literature, got a Ph.D. in Russian Literature, became an official translator of Aleksander Pushkin’s work and won a medal by the Russian government in recognition of her excellent work. Watch the video below with her 8 tips 🙂




Abutalebi J (2008) Neural aspects of second language representation and language control. Acta Psychol 128: 466–478.

Andrews, E., Frigau, L., Voyvodic-Casabo, C., Voyvodic, J., & Wright, J. (2013). Multilingualism and fMRI: Longitudinal Study of Second Language Acquisition. Brain sciences, 3(2), 849-76. doi:10.3390/brainsci3020849

Chomsky, N. (1965). Aspects of the theory of syntax / Noam Chomsky. (Special technical report / MIT Research Laboratory of Electronics ; no.11). Cambridge, Mass.: M.I.T. Press.

Curtiss. (Perspectives in neurolinguistics and psycholinguistics). New York [etc.] ; London:Academic Press.

Ferman, S., Karni, A. (2010). No childhood advantage in the acquisition of skill in using an artificial language rule. PLoS ONE, 5(10), E13648.

Hartshorne, Tenenbaum, & Pinker. (2018). A critical period for second language acquisition:Evidence from 2/3 million English speakers. Cognition, 177, 263-277.

Hubel, D., & Wiesel, T. (1959). Receptive fields of single neurones in the cat’s striate cortex. The Journal of Physiology, 148, 574-91.

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

Krashen, S. (1973). Lateralization, language learning, and the critical period. Language
Learning, 23, 63–74.

Kuhl PK, Ramírez RR, Bosseler A, Lin JF, Imada T. (2014). Infants’ brain activity in response to speech.


Norrman, G., & Bylund, E. (2016). The irreversibility of sensitive period effects in language development: Evidence from second language acquisition in international adoptees. Developmental Science, 19(3), 513-520.

Penfield, W. (1959). The Interpretive Cortex. Science, 129(3365), 1719-1725.

Skinner, B. (1957). Verbal behavior / B.F. Skinner. (The Century psychology series). New York: Appleton-Century-Crofts.

5 thoughts on “A critical period for language acquisition: let’s get critical”

  1. Pingback: Neuromyths and potential classroom implications: Part 4 – Language Window and Left or Right-brained – Education Development Courses

  2. Andre,

    I think that your first question in the article – Is language acquisition and language learning the same? – is confusing and untimely. Dr. Krashen answered this question about half a century ago: there is a great distinction between language acquisition and language learning.

    According to Krashen, there are two independent systems of second language performance: ‘the acquired system’ and ‘the learned system’. The ‘acquired system’ or ‘acquisition’ is the product of a subconscious process very similar to the process children undergo when they acquire their first language. It requires meaningful interaction in the target language – natural communication – in which speakers are concentrated not in the form of their utterances, but in the communicative act. The result of language acquisition, acquired competence, is also subconscious.

    The ‘learned system’ or ‘learning’ is the product of formal instruction and it comprises a conscious process which results in conscious knowledge ‘about’ the language, for example, knowledge of grammar rules. According to Krashen, talking (output) is not practicing; speaking in the target language does not result in language acquisition!

    A deductive approach in a teacher-centered setting produces ‘learning’, while an inductive approach in a student-centered setting leads to ‘acquisition’. According to Krashen ‘learning’ is less important than ‘acquisition’.

  3. Pingback: COVID-19, Remote Teaching, and the School Ecosystem: A Delicate Relationship – Education Development Courses

Leave a Reply

%d bloggers like this: