Cognitive and Language Development: Piaget, Vygotsky, Language, and Intelligence
Cognition and language items test stage theories, the mechanisms that drive change, and the milestones and theories of language acquisition.
Piaget's stages
- Sensorimotor (0–2): object permanence consolidates around 8–12 months. The A-not-B error (reaching to a previously correct hiding place) peaks around 8–12 months and fades near 12 months.
- Preoperational (2–7): symbolic play, egocentrism (three-mountains task), centration, irreversibility. Conservation of liquid quantity is typically failed until about age 7.
- Concrete operational (7–11): conservation, seriation, transitivity, class inclusion - but reasoning stays tied to concrete content.
- Formal operational (11+): hypothetico-deductive and abstract reasoning; not universally achieved.
- Critiques: violation-of-expectation studies suggest infants understand object permanence earlier; culture and schooling shape formal reasoning.
Vygotsky
Zone of proximal development, scaffolding, and private speech that internalizes into inner speech. Cognition is socially mediated and culturally tooled - a sharp contrast with Piaget's individual constructivism.
Language milestones
Cooing ~2 months; canonical (reduplicated) babbling ~6–7 months - deaf infants babble manually; first words ~10–15 months; vocabulary spurt around 18 months; telegraphic two-word speech ~18–24 months. Overextension (doggie for all animals) and underextension both occur. Overregularization ('goed,' 'mouses') at ~2.5–3.5 years shows rule learning, not simple imitation. In Brown's morpheme sequence, present progressive -ing appears early and irregular past forms typically precede regular -ed.
Theories
Behaviorist (Skinner: imitation and reinforcement - insufficient to explain novel utterances), nativist (Chomsky's LAD and the poverty-of-stimulus argument), and interactionist/usage-based (Bruner, Tomasello). Evidence for a sensitive period comes from Genie and from age-of-arrival effects on second-language attainment (Johnson & Newport).
Intelligence
Bayley Scales in infancy predict later IQ weakly; IQ stabilizes around age 7. The Flynn effect is the generational rise in scores. Fluid ability declines earlier than crystallized ability; the Seattle Longitudinal Study (Schaie) found many adults hold or improve into their 60s, with substantial individual variation.
Worked example
A 4-year-old says the tall narrow glass holds more juice than the short wide one. Reasoning: she centers on height and ignores width - centration - and cannot mentally reverse the pour. This is a preoperational reasoning pattern, not a counting or attention error, and it typically resolves near age 7 with concrete operations.
Traps that cost marks
- Calling the A-not-B error a failure of object permanence; it is usually a perseveration/motor-planning error.
- Reading 'egocentric' as 'selfish.'
- Treating overregularization as a mistake to be corrected rather than evidence of rule extraction.
- Assuming formal operational thinking is universal in adults.