Critical period for first language: the crucial role of language input during the first year of life.
Level 5 - mechanism / opinion, no new human data
Narrative review synthesizing observational case reports and natural experiments
PubMed 26111432 · doi:10.1016/j.conb.2015.06.003
What was done
Narrative review evaluating language outcomes in children who missed the critical window for first-language acquisition due to social isolation, hearing impairment, or abnormal brain development from infantile thiamine deficiency.
What was found
No quantitative data or effect sizes are reported in the abstract. The authors report that the critical period for acquiring syntax in a first language ends within the first year of life, and missing this window leads to severe long-term syntactic impairments.
Why it matters
Distinguishes the strict, early developmental timeline of first-language syntax acquisition from the broader windows observed in second-language learning, emphasizing the necessity of adequate linguistic input in infancy.
Limits
As a narrative review, it lacks a systematic search protocol, meta-analytic pooling, and reported sample sizes in the abstract. The conclusions rely on extreme natural experiments (profound deprivation, deafness, metabolic deficiency) that carry substantial potential confounding from overall cognitive, neurological, and psychosocial disruption.
Cited by
- partial If a child does not acquire language during the first several years of life, they can never acquire the fundamental concept of language.