A Very Brief Introduction to Developmental Psychology
Developmental Psychology is the study of how humans (and other animals)
change as they age. Most developmental psychologists study infants and children, but
some study adults. Some developmental psychologists study nonhuman animals in the
hope of finding general principles that apply to humans as well as to nonhuman
Cognitive Development: The Theory of Jean Piaget
Piaget emphasized that mental development results from the child actively
interacting with the physical environment – sucking things, grasping things,
manipulating things, and so on. From these experiences the child develops schemes,
mental representations of how things work. For example, the infant quickly develops a
scheme for nipples, that is, things to suck.
The development of schemes involves two contrasting processes, assimilation
and accommodation. In assimilation the child incorporates new experiences into its
existing cognitive structure, just like the digestive system extracts from what we eat the
components that can be incorporated into our bodies.
In accommodation the new experience does not fit in well with the existing
cognitive structure, so that structure is modified so the new experience can fit. Consider
a child who already has a “building blocks” scheme. It knows that you can stack blocks
one on top of another – but now it tries to put a block on top of a open box (a block with
no top). The block falls into the box. Hmm, that does fit neatly into the existing
cognitive structure, so the child accommodates by adding a “one thing inside another
Piaget proposed that there are four stages of cognitive development, and that
one cannot get to a later stage without going through all of the earlier stages.
The first stage is the Sensorimotor Stage, from birth to about 2 years of age. In
this stage the schemes are related to objects that are here now. They can be sucked,
banged, grasped, twisted, dropped, thrown, and so on – but when out of sight, they are
out of mind.
Next comes the Preoperational Stage, from about 2 years of age to 7 years of
age. The child in this stage has schemes for objects that are not present here and now.
Schemes are based on the appearances of objects rather than more abstract principles.
For example, children in this stage understand that wider things and taller things have
more stuff than narrow things and short thing, but they have not acquired the principle of
conservation of matter. Take two identical balls of clay. Verify that the child sees them
as being the same size. Now roll one out long and thin. Ask the child which one has
more clay. The child may respond that the long one has more or may respond that the
wide one has more.
Next comes the Concrete Operational Stage, from about 7 to 12 years of age.
Schemes have become more complex, but are still closely tied to experiences with
concrete objects in the physical world. For example, matter is conserved in this stage,
but that idea is closely tied to actual experiences – for example, the child has learned
that you can roll out a ball of clay, making it look different, but you can then roll it back
into a ball of the same size it was earlier.
Finally comes the Formal Operational Stage, starting about 13 years of age, if
ever. Schemes become yet more abstract. For example, the idea of conservation of
matter is adopted as a general principle, applying to all matter, not just to those objects
with which one has interacted. Theoretical thinking emerges in this stage.
Personality Development: Neo-Freudian Theory of Erik Erickson
Erickson was trained as a psychoanalyst, in Vienna. Rather than adopting
Sigmund Freud’s “theory” of five stages of psychosexual development, Erickson
developed his own theory with eight stages. Each stage is associated with a particular
conflict which must be resolved before advancing to the next stage, and they extend
across the entire lifespan – that is, personality development continues throughout life.
These conflicts, from earliest to latest, are”
1. Trust vs. Mistrust. Infancy. Can you rely on others (your parents)?
2. Autonomy vs. Shame/Doubt. Toddlerhood. Can you explore the world on your
3. Initiative vs. Guilt. Kindergarten. Can you plan your own activities, or should you
feel guilty about not asking your parents what to do?
4. Industry vs. Inferiority. Age 6 to puberty. Are you worthy or not compared to
5. Identity vs. Role Confusion. Teenage years. Who am I? How do I fit in? What
should I do with my life?
6. Intimacy vs. Isolation. Young adulthood. Do I want to settle down with someone,
and if so, whom?
7. Generativity vs. Stagnation. Mid-Life. Have I helped the younger generation
grow or not.
8. Ego Integrity vs. Despair. Old age. Am I happy with what I have accomplished
in life or do I despair at not having accomplished what I wish I had.
Social Development: Basic Research with Monkeys
Harry Harlow studied the development of attachment in infant rhesus monkeys.
As you know, monkeys are closely related to humans (both are primates), and the
processes of attachment in monkeys is expected to be similar to that in humans. With
certain types of research there would be greater ethical and other problems doing the
research with human infants than with monkey infants, so Harlow studied the monkeys
instead of humans.
In one study Harlow raised infant monkeys in individual cages, all alone, except
for the presence of two “surrogate” mother. One of the surrogate mothers was made of
hardware cloth and the other surrogate was covered with terry cloth. For half of the
infants hardware cloth surrogate had nipple from which the infant could feed, but the
terry cloth surrogate had no nipple. For the other half of the infants it was the terry cloth
surrogate which had the nipple.
To which of these two surrogates do you think that the infant monkeys became
One could argue that they should become attached to the surrogate that gave it
milk – after all, food is a primary reinforcer, and the basic laws of conditioning would
predict that the surrogate with the nipple should acquire secondary reinforcing power.
Harlow operationalized attachment as the amount of time the infants spent
clinging to the surrogates and which surrogate did the infant run to when frightened.
Here is a summary of the results:
As you can see, regardless of which surrogate had the nipple, the infants spent
most of their time clinging to the soft surrogate covered with terry cloth.
In addition, when frightened it was the terry cloth surrogate to which the infants
ran, regardless of whether it had the nipple or not.
Harlow also found that when exploring a new area, the infants were more
adventuresome when the cuddly surrogate was with them than when the wire surrogate
was with them. The secondary reinforcing value of the cuddly surrogate was confirmed
by showing that the infants would learn to press a lever to open a window allowing them
to see, briefly, the cuddly surrogate.
So, what was the primary reinforcer provided by the cuddly surrogate. To make
his results fit in with learning theory, Harlow proposed that the cuddly surrogate
provided “contact comfort” as a primary reinforcer. One could just as well say that infant
monkeys’ brains are born with the knowledge that Mom is cuddly.
Harlow could not have done this research with human infants, but what he
learned from studying monkeys made an important contribution to our understanding of
the development of attachment in primates, including monkeys and humans.