IELTS Reading 128: The Closing Window

Adapted from arXiv / Scientific American / Frontiers in Psychology (2025-2026). IELTS Reading Section 3 difficulty, approximately 1,050 words. Source: https://www.scientificamerican.com/article/babies-brains-recognize-foreign-languages-they-heard-before-birth/

🎧 Audio

Reading Passage

A. The ease with which a small child picks up a language — any language, several at once — has puzzled linguists for centuries. A toddler does not study grammar; she absorbs it from the speech around her, producing novel sentences no adult has ever taught her, by the age of three or four already wielding a phonological system that adult learners spend decades chasing. In 1967, Eric Lenneberg proposed that this effortless ability reflected a biologically determined window: the brain, he argued, was uniquely plastic for language during childhood, and that window closed around puberty, after which full native-like mastery became effectively impossible. The Critical Period Hypothesis became one of the most influential ideas in twentieth-century linguistics, shaping everything from classroom foreign-language teaching to debates over immigration and bilingual education. But half a century later, the picture it painted is turning out to be both more nuanced and more interesting than Lenneberg imagined. The modern debate is no longer whether a critical period exists — that is not disputed — but when exactly it ends, which aspects of language it constrains, and what happens to the adult learner's brain when the window begins to close.

B. The first challenge came from infants themselves. A study published in Nature Communications Biology in 2025, led by researchers in Montreal, used brain imaging to show that newborns who had heard short stories in foreign languages while still in the womb processed those languages in ways indistinguishable from their mother tongue. Fetuses, it turns out, are already listening: by the third trimester, the auditory system is functional, and the rhythms, intonation contours and familiar cadences of the maternal voice are encoded in memory before birth. After birth, infants continue as universal listeners — able to distinguish phonemic contrasts from every human language until roughly six to twelve months of age, when perceptual narrowing begins: they lose the ability to reliably tell apart sounds that do not occur in their native environment. This sensitive period for phonetic learning is one of the earliest developmental milestones, and infant performance at six to twelve months predicts later language trajectories up to school entry.

C. The second challenge came from the far end of the lifespan. If the critical period ended at puberty, then adults who learned a second language after puberty should systematically fail to reach native-like intuition, regardless of effort. Yet large-scale studies of late bilinguals have found that motivated adults can — though rarely do — achieve near-native pronunciation and grammar, and that the adult brain itself undergoes measurable structural and functional reorganization when acquiring a new language, even in middle age. A 2025 review in Frontiers in Human Neuroscience concluded that neuroimaging studies continue to detect changes in frontal and temporal white matter even in older second-language learners, undermining the claim that adult language acquisition is fundamentally different in kind. A more radical revision came from a 2026 analysis of syntactic attainment, which found that the capacity for optimal grammar learning does not terminate abruptly at puberty but persists almost to the late teens — declining gradually after about 17.4 years of age, rather than shutting off on a single developmental date. The distinction matters: a gradual decline means that late starters can still reach high levels with sufficient motivation and practice, whereas a hard cutoff would imply that adult learning is inherently futile.

D. Why should the window close at all? One recent computational explanation, published on arXiv in 2025, attributes the decline not to some mysterious loss of brain plasticity but to the maturation of working memory. Young children, the model argues, hold fewer items in memory at once, which forces them to extract structural regularities rather than memorising individual sentences. As working memory expands during adolescence, learners can compensate for weak implicit grammatical knowledge with explicit memorisation — a strategy that gets them by but prevents the deep, automatic encoding that produces native-like intuition. On this view, the critical period is not a barrier that puberty erects; it is a side-effect of cognitive development that makes adult learning harder, not impossible. A separate longitudinal study of autistic children, reported on medRxiv in 2025, found that upward transitions in language-comprehension phenotypes became rare after about ten years of age, consistent with a developmental boundary that applies across typical and atypical development alike. On this computational view, the critical period is not a biological gift that puberty withdraws but a trade-off built into the architecture of learning: children's limited memory capacity forces abstraction, and adolescents' expanding memory capacity permits shortcuts that are faster but shallower.

E. What does this mean for teaching? If Lenneberg's sharp cut-off is wrong, then postponing foreign-language instruction until secondary school — as many education systems do — is not the catastrophic loss once assumed, though early exposure clearly confers an advantage in pronunciation and accent. Adult learners benefit from explicit grammar instruction, deliberate practice and immersive environments in ways that children do not require, and they can still reach functional fluency quickly. But the evidence also suggests that the best way to produce native-like intuition is simply to start young and stay long: motivation, immersion and consistent practice matter at every age, but they cannot entirely manufacture the automatic phonetic calibration that happens between six months and three years. The modern view, then, is not that language learning is a race with a hard finish line, but that different skills — phonology, grammar, vocabulary — mature at different rates, and that no single age neatly separates "successful" from "impossible" acquisition. This revised picture has practical consequences for immigration and education policy: it suggests that adult immigrants who never fully erase their foreign accent are not failing at learning — they are behaving exactly as the mature brain is expected to behave, and can still reach functional fluency well within the normal range of human communication.

Questions 1-4

Choose the correct heading for paragraphs B, C, D and E from the list of headings below.

List of Headings i. The fetal and infant origins of language perception ii. Why the window closes: working memory and cognitive development iii. Challenges from adult bilinguals and the revised timeline iv. Implications for language teaching v. Lenneberg's original hypothesis vi. How infants distinguish all human languages vii. The role of genetics in bilingualism

1. Paragraph B: ____
2. Paragraph C: ____
3. Paragraph D: ____
4. Paragraph E: ____

Questions 5-8

Choose the correct letter, A, B, C or D.

5. According to Lenneberg's original hypothesis, when did the language learning window close? A. At birth. B. Around puberty. C. At age five. D. Never.

6. What did the 2025 Montreal study find about newborns? A. They cannot hear in the womb. B. They processed foreign languages heard in the womb like their native tongue. C. They preferred English over all other languages. D. They learned no language before birth.

7. According to the 2026 syntactic attainment analysis, when does optimal grammar learning end? A. At about 17.4 years of age. B. At puberty, around 12. C. At age five. D. It never ends.

8. What does the working-memory model suggest? A. Children have better working memory than adults. B. Expanding working memory allows memorisation but prevents deep grammatical encoding. C. Adults should stop learning languages. D. Language ability is purely genetic.

Questions 9-13

Do the following statements agree with the claims of the writer?

Write:

• TRUE if the statement agrees with the information
• FALSE if the statement contradicts the information
• NOT GIVEN if there is no information on this

9. Infants under six months can distinguish phonemic contrasts from all human languages.
10. Adults who learn a second language can never achieve any level of proficiency.
11. The sensitive period for phonetic learning is between six and twelve months of age.
12. The autistic children study found that language phenotype transitions became more common after age ten.
13. Bilingualism improves IQ significantly.

Questions 14-15

Complete the summary below using NO MORE THAN TWO WORDS from the passage.

The Critical Period Hypothesis originally proposed that full language mastery became impossible after (14) __________. Recent research revises this, suggesting that the optimal window for grammar learning extends to about 17.4 years and that (15) __________ memory maturation may explain why.

Answers & Explanations

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