Which group provides robust evidence for the critical period hypothesis?

Which group provides robust evidence for the critical period hypothesis?

• A. Early bilinguals who spoke from birth.
• B. Children with no exposure to language.
• C. Late L1/L2 learners and sign language users.
• D. Non-human primates.

Answer: (C)

The main idea being tested is that there is a limited window in development during which language can be acquired with native-like proficiency, especially for pronunciation and grammar. The strongest evidence for this comes from people who start learning a language after this window has closed: late L1/L2 learners and late sign language users. Across both spoken and signed languages, these learners often reach communicative competence but struggle to achieve native-like accuracy in phonology and syntax, showing persistent non-native patterns even with extensive exposure and effort. This pattern supports the notion of a biologically bounded period of high plasticity for language learning, after which attaining native-like mastery becomes much harder. In contrast, individuals who begin language very early tend to reach native-like levels, those with no language exposure cannot develop language, and data from non-human primates do not map neatly onto human language development, making late human learners the most informative group for this question.

The main idea being tested is that there is a limited window in development during which language can be acquired with native-like proficiency, especially for pronunciation and grammar. The strongest evidence for this comes from people who start learning a language after this window has closed: late L1/L2 learners and late sign language users. Across both spoken and signed languages, these learners often reach communicative competence but struggle to achieve native-like accuracy in phonology and syntax, showing persistent non-native patterns even with extensive exposure and effort. This pattern supports the notion of a biologically bounded period of high plasticity for language learning, after which attaining native-like mastery becomes much harder. In contrast, individuals who begin language very early tend to reach native-like levels, those with no language exposure cannot develop language, and data from non-human primates do not map neatly onto human language development, making late human learners the most informative group for this question.