In other words, at each successive stage, it's not just a matter of doing something better, but of doing a different thing altogether. The function of cognitive growth is to produce increasingly powerful cognitive structures that permit the individual to act on the environment with greater flexibility. The sensorimotor period ranges from birth to about age 2. Infants learn mostly through trial and error learning. Children initially rely on reflexes, eventually modifying them to adapt to their world.
Behaviors become goal directed, progressing from concrete to abstract goals.
For example, if you place a toy under a blanket, the child who has achieved object permanence knows it is there and can actively seek it. Before this stage, the child behaves as if the toy had simply disappeared. The attainment of object permanence generally signals the transition to the next stage. The preoperational period ranges from about ages 2 to 7. They are able to focus on only one aspect or dimension of problems.