AP Psychology 3.4: Cognitive Development Across the Lifespan

Point at an airplane overhead and a toddler who has just learned the word bird may shout "bird!" Jean Piaget, who spent decades watching children reason, would say she is using a schema, a mental framework for organizing what she knows. Her bird schema says, roughly, that things flying in the sky are birds.

Piaget described two ways schemas develop. In assimilation, a child takes in new information by fitting it into a schema she already has, without changing the schema. Calling the airplane a bird is assimilation. In accommodation, the child changes the schema to fit the new information. When she learns that airplanes are machines that carry people, and starts sorting flying things into birds and planes, she has accommodated.

This kind of adjusting goes on all the time, a little at a time, so it is a continuous process. Piaget also saw moments when a child's whole way of thinking shifts, so that she reasons in a way she could not before. He called these stages, and the move from one stage to the next is discontinuous, a step rather than a slope. His theory needs both: steady adjustment of schemas within a stage, and a change in kind between stages.

Piaget's stages come in the same order for every child, though the timing varies.

• Sensorimotor stage, from infancy through toddlerhood. Babies learn through their senses and their actions. The big gain is object permanence, knowing that things still exist when out of sight. Before it, a toy hidden under a blanket is simply gone.
• Preoperational stage, from toddlerhood through early childhood. Children get good at using mental symbols, such as words and drawings, and at pretend play, where a stick becomes a sword. The stage is known as much for what children cannot yet do. They fail at conservation, understanding that an amount stays the same when its shape changes, and at reversibility, running an action backward in their heads. They show animism, giving lifeless things feelings and intentions, and egocentrism, trouble taking another person's point of view. During this stage children also begin to develop a theory of mind, the understanding that other people have thoughts and beliefs that can differ from their own.
• Concrete operational stage, from early through late childhood. Children correct those errors and think logically and realistically about concrete things. They still struggle to think systematically, such as planning how to test every possibility in turn.
• Formal operational stage, from late childhood through adulthood. People can think abstractly and hypothetically, about ideas and about what could be. Piaget proposed that not everyone reaches this stage.

Piaget pictured a child working the world out largely on her own, like a small scientist. Lev Vygotsky, a psychologist working at about the same time, put other people at the center. To him, children are social learners. They learn by interacting with parents, teachers, older siblings and friends, inside a sociocultural context: the language, tools and customs of the community around them. A child in a fishing town and a child in a big city learn different skills, because the people around them know and teach different things.

Vygotsky's best-known idea is the zone of proximal development, the range between what a child can do alone and what she can do with help from someone more skilled. A task she can already do alone teaches her little. A task far beyond her is too hard even with help. Learning happens best in between, and Vygotsky held that this zone is where teaching should aim.

The help itself is called scaffolding. Like the scaffolding around a building under construction, it is support put up while it is needed and taken down bit by bit as the learner can stand on her own. A parent teaching a child to tie her shoes might first make the loops with her, then only say "now pull it through," then only watch.

Thinking keeps changing after childhood, though not in stages. Psychologists separate two kinds of intelligence that age differently.

Crystallized intelligence is the knowledge and skill you have built up: vocabulary, facts, how to do your job, how to handle familiar kinds of problems. It remains relatively stable through adulthood. Fluid intelligence is the ability to reason quickly about problems that are new to you, such as working out a kind of puzzle you have never seen. It tends to wane as people age.

So a 70-year-old may take longer than a 25-year-old to figure out a new phone app and still know as many words as ever and explain a complicated situation more clearly. Both of those are part of typical aging.

Some changes are not. Dementia is a cognitive disorder in which memory and other thinking abilities decline far enough to interfere with everyday life, such as handling money or finding the way along a familiar route. It is caused by disease or damage in the brain, and Alzheimer's disease, which you met in the memory topics, is its most common cause. Dementia is not a normal part of growing older, and most older adults do not have it. Forgetting a name and recalling it later is ordinary; dementia is a lasting decline that usually worsens over time.