Which stage is characterized by object permanence?

Concept: In Jean Piaget's theory of cognitive development, object permanence is the understanding that a thing continues to exist even when it is no longer seen, heard or touched. Piaget treated it as the first great achievement of infancy: before a child can use symbols or reason logically, it must first grasp that objects are separate from its own actions and endure independently of them.

Application: The stem asks which of Piaget's four stages is characterised by that achievement. It belongs to the sensorimotor stage, from birth to roughly two years, in which the infant knows the world only through sensation and movement. Piaget's hidden-object task marks the transition: before about eight months an infant stops reaching for a toy the moment a cloth covers it, as though the toy had ceased to exist; from about eight to twelve months the infant lifts the cloth and retrieves it. By the close of the stage, at roughly eighteen to twenty-four months, the child holds a stable mental image of an absent object; that stable image is what allows deferred imitation to appear at the very end of this same stage, and it is the basis on which symbolic and pretend play expand in the stage that follows.

Cross-check: Setting all four stages side by side shows that no later stage is defined by this achievement — each later stage is defined by a further advance that already takes it for granted.

Object permanence therefore characterises the sensorimotor stage.