1. Sensorimotor stage. This stage typically lasts from birth to about two years of age. In this stage, children understand the world through their sensory perceptions and motor behaviors. In other words, children understand by perceiving and doing. The most important achievement of this stage is the capability to use mental symbols to represent objects and events. The acquisition of object permanence—

that is, knowing that objects exist even when they cannot be seen—illustrates this achievement. Early in this stage, children appear to assume that when a toy or other object is hidden (e.g., when a ball rolls under a sofa), it ceases to exist. Later in this stage, children will search under the sofa for the lost ball, demonstrating that they have come to understand that objects exist continuously.

Other cognitive developments that also depend on the development of mental representation typical of this stage include deferred imitation and language acquisition. These developments have important implications for later cognitive development and enculturation. Imitation is an important cognitive component of observational learning, and language skills are necessary to ensure proper communication of verbal socialization processes.