Brain development (maturation & critical periods)
IB Psychology· Human development· 14 min read
1. Core concept
The developing brain is built by biological maturation and then sculpted by experience. Early in life it over-produces neural connections; those that are used are strengthened and those that are not are pruned away, so experience physically shapes the wiring (neuroplasticity). Some abilities depend on the right input arriving during a limited window — a critical or sensitive period — after which they are much harder, or impossible, to acquire. Development is therefore neither purely 'nature' nor purely 'nurture' but the timed interaction of the two.
2. Key studies
IB Psychology answers must be supported by named studies. Learn these to cite as evidence:
Werker et al. (1981)
Infants of any language background could discriminate non-native (Hindi) speech sounds that English-speaking adults could no longer tell apart. — Evidence for experience-driven pruning on a maturational timetable — an early ability narrowed during a sensitive period.
Curtiss et al. (1974)
The case study of Genie, deprived of language exposure throughout childhood, found she did not acquire normal language (especially grammar) despite later intervention. — Illustrates a critical period — input missed during the developmental window could not later be fully made up.
3. Evaluation (AO3)
Strength — converging animal and human evidence — Human developmental data (Werker), deprivation cases (Genie) and controlled animal work (Blakemore & Cooper's kittens) point the same way, so the plasticity/critical-period account is well supported.
Limitation — 'critical' is often too strong, and cases don't generalise — Many windows are better described as sensitive (softer edges, some later recovery) than strictly critical; and a single confounded case like Genie — abuse, malnutrition, possible prior disability — cannot on its own prove a language critical period.
4. Scope
5. Common Pitfalls
Wrong move:
A 'critical period' is a hard deadline that applies to all learning, and a window once missed can never be recovered.
Why:
A frequently penalised misconception in IB Psychology exams.
Correct move:
Most developmental windows are sensitive periods with softer edges — learning is easiest then but not strictly impossible afterwards. Strict 'critical' periods (no later recovery) apply to only a few systems.
Going deeper
- Neuroplasticityneuroplasticity — pruning and experience-dependent change (Blakemore & Cooper) — is the biological-approach concept HD applies to development.
- Childhood experiences & epigeneticshow experience leaves lasting biological traces is developed as childhood experiences & epigenetics (HD_8).