What is the critical period hypothesis for language development, and what are two lines of evidence supporting it?

What is the critical period hypothesis for language development, and what are two lines of evidence supporting it?

• A. A proposed window in early childhood during which language acquisition occurs most easily; evidence includes poorer outcomes after late L1 exposure and robust findings in late L1/L2 learners and sign language.
• B. A theory that language can only be learned before age 5; supported by adult learners.
• C. The idea that language is learned best after puberty; supported by L2 success.
• D. The notion that language is purely genetic with no critical window.

Answer: (A)

The critical period hypothesis for language development says there’s a window in early childhood during which language learning happens most easily and naturally, and after that window, acquiring native-like proficiency becomes much harder, with outcomes that are often poorer in grammar, pronunciation, and overall competence. One line of evidence comes from late exposure to a first language. When children miss the early period and are exposed to a first language only after infancy, they typically show lasting difficulties in core aspects of language, such as grammar and syntax, and their pronunciation often never reaches native-like levels. This pattern suggests that missing the early window can lead to persistent language deficits. A second line of evidence comes from studies of late exposure to language more generally, including second-language learners and sign-language learners. Across these cases, earlier exposure tends to yield higher ultimate proficiency, especially in phonology and grammar, while starting later is associated with persistent differences from native speakers. Sign language studies reinforce this idea by showing that individuals without early exposure to a natural language—even in a different modality—often struggle to acquire fully native-like proficiency, pointing to a timing effect that spans languages and modalities. Together, these lines of evidence support the view that a period in early childhood is particularly conducive to achieving native-like language mastery, with later exposure making it much more challenging to reach that level.

The critical period hypothesis for language development says there’s a window in early childhood during which language learning happens most easily and naturally, and after that window, acquiring native-like proficiency becomes much harder, with outcomes that are often poorer in grammar, pronunciation, and overall competence.

One line of evidence comes from late exposure to a first language. When children miss the early period and are exposed to a first language only after infancy, they typically show lasting difficulties in core aspects of language, such as grammar and syntax, and their pronunciation often never reaches native-like levels. This pattern suggests that missing the early window can lead to persistent language deficits.

A second line of evidence comes from studies of late exposure to language more generally, including second-language learners and sign-language learners. Across these cases, earlier exposure tends to yield higher ultimate proficiency, especially in phonology and grammar, while starting later is associated with persistent differences from native speakers. Sign language studies reinforce this idea by showing that individuals without early exposure to a natural language—even in a different modality—often struggle to acquire fully native-like proficiency, pointing to a timing effect that spans languages and modalities.

Together, these lines of evidence support the view that a period in early childhood is particularly conducive to achieving native-like language mastery, with later exposure making it much more challenging to reach that level.