Psychology 101 – Development I: Physical and Cognitive Development



Piaget was fascinated with children…

The first psychologist to trace cognitive development systematically was Jean Piaget (1896-1980). Piaget had a keen interest in epistemology, the branch of philosophy concerned with the nature of knowledge. The British empiricist philosophers, such as John Locke, argued that all knowledge comes from experience. To know what a dog is like, a person has to examine a number of dogs, experience them with the senses and come to some conclusions about their common properties. In contrast, German philosopher Immanuel Kant argued that some forms of knowledge do not come from observation, but are innate. Kant’s ideas were the starting point for Piaget’s life work. He believed that Kant was both right and wrong with his theories. Kant was right, in the sense that people’s understanding of time, space and logic is not simply formulated from experience, but he was wrong, Piaget thought, in that people were born with this knowledge. Piaget (1970) proposed that children develop knowledge by inventing or constructing reality out of their own experience, mixing what they observe with their own ideas about how the world works.

Assimilation and Accommodation – Piaget viewed intelligence as the individual’s way of adapting to new information about the world. He asserted that children cognitively adapt to their environment through two interrelated processes, assimilation and accommodation. Assimilation involves interpreting actions or events in terms of one’s present schemas – that is, fitting reality into one’s existing ways of understanding. According to Piaget, a schema is an organised, repeatedly exercised pattern of thought or behaviour. If humans only assimilated information into existing schemas, no cognitive development would take place. The second process, called accommodation, is the modification of schemas to fit reality. For Piaget, the driving force behind cognitive development is equilibration – that is, balancing assimilation and accommodation to adapt to the world. When a child comes across something he does not understand, he finds himself in a state of cognitive disequilibrium that motivates him to make sense of what he has encountered. He may attempt to fit it into existing schemas (assimilation) or he may combine schemas or construct an entirely new schema to fit the new reality (accommodation). For example, an infant who is brought in front of a mirror by his father, will have trouble coming to terms with the fact that the baby in the mirror is actually him and that he doesn’t have two fathers – the one holding him and the one holding another baby in front of him. Eventually he constructs the understanding that a mirror is a special kind of surface that reflects images, and he will accommodate this into a new schema.

Stages of Cognitive Development


Approximate Ages (years)




Thought and action are virtually identical, as the infant explores the world with its senses and behaviours; object permanence develops, the child is completely egocentric.



Symbolic thought develops; object permanence is firmly established; the child cannot coordinate different physical attributes of an object or different perspectives.

Concrete Operational


The child is able to perform reversible mental operations on representations of objects; understanding of conservation develops; the child can apply logic to concrete situations.

Formal Operational


The adolescent or adult can apply logic more abstractly; hypothetical thinking develops.

Sensorimotor Stage (0-2) – The sensorimotor stage, in which infants think with their hands, mouths and senses, lasts from birth to about two years of age. Sensorimotor thought primarily takes the form of action, as infants learn about the world by mouthing, watching and manipulating objects. According to Piaget, the practical knowledge infants develop during this period forms the basis for their later ability to represent things mentally. The term sensorimoter emphasises that infants are bound by their sensations and actions and are capable of little explicit reasoning beyond what they are sensing and doing.

object permanenceA major achievement of the sensorimotor stage is the development of object permanence, the recognition that objects exist in time and space independent of the child’s observations or actions towards the object. According to Piaget, before the age of about 12 months, an object such as a ball exists for an infant only when it is in sight; if it is hidden from view, it no longer exists! When a child acquires object permanence, he will look for the ball, even when it is hidden from view, and he will be delighted to find it. Piaget suggested that the attainment of object permanence lies behind infants’ endless fascination with games such as peek-a-boo, which confirm their new understanding. During the sensorimotor stage, children are extremely egocentric, they are thoroughly embedded in their own point of view. When an infant closes her eyes, the whole world becomes dark; when a ball is no longer in view, it ceases to exist. In a way they see themselves as little Gods. For Piaget, development entails gradual movement away from egocentrism towards a recognition of alternate points of view, particularly the points of view of others.

Preoperational Stage (2-7) – The preoperational stage begins roughly around age two and lasts until ages five to seven. It is characterised by the emergence of symbolic thought – the ability to use symbols to represent concepts. Once children learn to manipulate symbols and mental images, thought becomes detachable from action. To put it in another way, when children can play with the world in their minds, then no longer have to think exclusively with their hands and mouths. Symbolic thought allows preschool children to converse with other people and to imagine solutions to problems before actually doing anything physically. A limitation of preoperational thought is centration, the tendency to centre their focus on one perceptually striking feature of an object without considering other features that might be relevant. Children in this stage are still fairly ecocentric, but significantly less so than in the sensorimotor stage; they no longer think the world revolves around them, but are still unable to view things from another person’s perspective.

Concrete Operational Stage (7-12) – The third stage of cognitive development, called the concrete operational stage, occurs roughly between the ages of 7 to 12. At this point, children are capable of mentally manipulating internal representations of concrete objects in ways that are reversible. In other words, children can imagine altering a set of objects, and can then mentally put them back to the way they found them. For example, school age children are able to imagine different ways of explaining why they haven’t done their homework, picture the likely consequence of each excuse, and pick the one with the highest perceived chance of acceptance. In contrast, younger children will either blurt out a ridiculous lie or tell the truth, much to the amusement of cognitively superior adults.

The major achievement of the concrete operational stage is the child’s ability to understand the concept of conservation, that basic properties of an object or situation remain stable even though superficial properties may change. For example, a child in this stage knows that liquid being poured from a small but thick glass into a tall and thin glass of the same volume, is the same liquid with the same volume, even though the glasses appear to be of different sized. Similarly, a child can squash a ball of clay or play dough, and understand that the clay is still the same clay, it is just a different shape after being squashed.

Formal Operational Stage (12+) – Piaget’s fourth and final stage begins roughly around ages 12-15. The formal operational stage is characterised by the ability to manipulate abstract as well as concrete objects, events and ideas mentally. Another hallmark of the formal operational stage is the new ability to be able to think about and manipulate hypothetical scenarios, ‘what if’ situations that elaborate on made up situations and their consequences. It is during this stage that children become fascinated by questions such as, ‘would you rather be eaten quickly – by a lion, or very slowly – by ants?’ Or maybe that was just me…
And that about covers this part on human development.

Check Out Part 7 of Psychology 101: Development II – Social Development!

Other guides in the Psychology 101 series:

6 thoughts on “Psychology 101 – Development I: Physical and Cognitive Development

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