3.4 Cognitive Development Across the Lifespan

Jean Piaget argued that children aren't just less-informed adults; they think in qualitatively different ways. They build schemas, mental frameworks for understanding the world, through assimilation (fitting new experiences into existing schemas) and accommodation (changing schemas to fit new experiences). A toddler who calls a zebra a 'horse' is assimilating; learning that zebras are different is accommodating. Piaget saw both continuous growth (schemas gradually refined) and discontinuous change (distinct stages).

Concrete operational children handle real, concrete problems well but struggle with abstract, systematic thinking, such as testing every combination in a science problem. Formal operational thinkers can reason about hypotheticals ('What if...?') and abstract ideas like justice. Piaget believed not everyone reaches formal operations. Later research suggests children often reach some milestones earlier than he thought, and that development is more gradual and varies more across cultures than strict stages imply.

• Object permanence (sensorimotor): knowing that objects still exist when out of sight. Before it develops, a baby stops searching for a toy hidden under a blanket.
• Egocentrism (preoperational): difficulty taking another person's point of view. A 3-year-old may hold up a drawing to show you over the phone.
• Animism (preoperational): believing that objects are alive and have feelings, such as thinking the moon is following you.
• Conservation: understanding that quantity stays the same when shape changes. A preoperational child thinks a tall, thin glass holds more juice than a short, wide one, even after watching the same juice poured between them.
• Reversibility: understanding that an action can be undone, like pouring the juice back. Its absence is part of why preoperational children fail conservation tasks.
• Theory of mind: understanding that other people have their own thoughts, beliefs and feelings, which may differ from yours. It typically develops in the preoperational years, around age 4 or 5.

Lev Vygotsky emphasized that children learn through interaction with other people within their culture. The zone of proximal development (ZPD) is the range between what a child can do alone and what they can do with help from a more skilled person. Scaffolding is the temporary support an adult or more skilled peer gives within that zone, like hints, demonstrations or breaking a task into steps, which is gradually removed as the child gains skill. A parent holding the back of a bike seat, then letting go for longer and longer stretches, is scaffolding.

Crystallized intelligence is your accumulated knowledge and verbal skill, like vocabulary and facts. It stays stable or even grows through most of adulthood. Fluid intelligence is your ability to reason quickly and solve new problems, and it tends to decline gradually with age. That's why older adults often do well on vocabulary tests but slower on speed-based puzzles.

Dementia is a decline in memory and other thinking abilities severe enough to interfere with daily life. It is not a normal part of aging. Alzheimer's disease (2.5) is its most common cause.