# Brain development (maturation & critical periods)

> IB Psychology · IB Psychology 2027 First Assessment
> Source: https://www.owlsprep.com/study/ib-psychology-hd-brain-development-maturation-and-critical-periods/

The role of brain maturation in human development. The extent to which critical periods explain human development. The role of neuroplasticity in human development.

## Learning objectives

- The role of brain maturation in human development. The extent to which critical periods explain human development. The role of neuroplasticity in human development.

## How often is this tested?

Based on OwlsPrep's analysis of official CIE IB_PSYCH P2 past papers (2019–2025): **Brain development (maturation & critical periods)** appears **10 times** in the last 7 years — **3.5%** of all P2 questions (10 of 288).

Most-tested forms: Essay: Discuss (22 marks) (5), Essay: To what extent (22 marks) (3), Essay: Evaluate (22 marks) (2).

## 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.

## 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.*

## 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.

## Scope

> **note**
>
> The maturation–plasticity–critical-period story of the developing brain is the focus. The general mechanism of neuroplasticity lives in the biological approach (BIO_8); the molecular route from early experience to lasting change is HD_8.

## Common pitfalls

- **Wrong:** A 'critical period' is a hard deadline that applies to all learning, and a window once missed can never be recovered.
  - Why it fails: A frequently penalised misconception in IB Psychology exams.
  - Correct: 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.

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