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piaget[f85,jmc]		Piaget's stages of intelligence

reference and quote from Robert J. Sternberg, Human Intelligence: The Model
is the Message, Science, 1985 December 6, vol. 230, Number 4730, pp. 1111-1118

J. Piaget, The Psychology of Intelligence (Littlefield Adams, Totowa, N.Y. 1972)

A biological model: Intelligence as an evolving system.  Piaget's (40) theory of
intelligence is so rich and variegated that it is impossible to do justice
in a brief summary.  The theory is heavily grounded in the biological
notion that survival depends on adaptation to the environment, and hence,
that intelligent survival requires intelligent adaptation.
There are perhaps three particularly crucial aspects to Piaget's theory. 
The first is the notion of the schema, which is an organized sequence of 
mental structures and steps for accomplishing a given set of tasks.  The
second is the notion of equilibrium--that the organizm acquires cognitive
capacity through a delicate balance of two cognitive mechanisms, namely,
assimilation and accommodation. In assimilation, the organism fits new 
environmental inputs into its existing cognitive schemata.  In accommodation,
the organism transforms its cognitive schemata so as to accept the environmental
inputs.  Thus,accommodation, but not assimilation, requires restructuring of
one's cognitive system.

The third critical aspect of Piaget's theory is his concept of incremental
periods of intellectual development that build upon one another. In the
sensori-motor period (lasting from birth to approximately 2 years of age), the
infant interacts with the environment through relatively simple, overt 
sensory and motor schemata.  In the preoperational period (lasting 
roughly from age 2 to age 7) the child acquires the ability to let one
object represent another that is not present; in other words, the infant
uses advanced symbolic capacity. In the concrete-operational period
(lasting roughly from age 7 to age 12), the child can apply mental
operations to concrete objects--for example, the child may realize that if one
pours water from a tall thin vessel to a short fat one, the amount of water
is conserved and hence remains the same.  In the formal-operational period
(lasting roughly from age 12 on), the child can apply mental operations to
abstract or formal objects, realizing, for example, not only relations 
between objects but also higher order relations between relations (as in 
thinking by analogy).  Thus, the intellectual development of the child is
characterized by the maturation over time of increasingly broad and complex
cognitive function.