-in Substage 1, babies suck, grasp, and look in much the same way, no
matter what experiences they encounter
Repeating Chance Behaviours - around 1 month, as babies enter
Substage 2, they start to gain voluntary control over their actions through
the primary circular reaction, by repeating chance behaviours largely
motivated by basic needs; babies in this substage also begin to vary their
behaviour in response to environmental demands.
During Substage 3, from 4 to 8 months, infants sit up and become skilled
at reaching for and manipulating objects - motor achievements that
strengthen the secondary circular reaction, through which they try to
repeat interesting events in the surrounding environment that are cuased
by their own actions.
Intentional Behaviour - in Substage 4, 8- to 12-month-olds combine
schemes into new, more complex action sequences; 8- to 12-month-olds
can engage in intentional, or goal-directed, behaviour, coordinating
schemes deliberately to solve simple problems.
Object permanence - the understanding that objects continue to exist
when they are out of sight; this awareness is not yet complete; babies still
make the A-not-B search error: if they reach several times for an object
at one hiding place (A), then see it moved to another (B), they still search
for it in the first hiding place (A).
In Substage 5, from 12 to 18 months, the tertiary circular reaction, in
which toddlers repeat behaviours with variation, emerges.
Mental Representation - in Substage 6, sensorimotor development
culminates in mental representation; one sign of this capacity is that 18- to
24-month-olds arrive at solutions to problems suddenly rather than
through trial-and-error behaviour, apparently experimenting with actions
inside their heads - evidence that they can mentally represent experiences.
Representaiton also enables older toddlers to solve advanced object-
permanence problems involving invisible displacement; second, it permits
deferred imitation - the ability to remember and copy the behaivour of
models who are not present; it makes possible make-believe-play, in
which children act out everyday and imaginary activities.
Follow-Up Research on Infant Cognitive Development
-to discover what infants know about hidden objects and other aspects of
physical reality, researchers often use the violation-of-expectation