Infancy

Cognition, comprised of mental processes such as conceiving, reasoning, memory, and symbolization, organizes humans' action in and perception of the world and is the foundation of humans' status as psychological beings. Speculation over the developmental origin of cognition has fueled philosophical inquiry for millennia. The modern study of infant cognitive development takes its own origin from the theory and research of Swiss psychologist Jean Piaget.

According to Piaget, infants are born with no mental framework in place and only gradually construct a conceptualization of the world through their experience with it. The experience of the infant is initially bound by the immediacy of perception and action, a "sensorimotor intelligence." Piaget argued that newborns have no concept of self or object and simply experience a wash of sensations. Only rudimentary schemas for interacting with the world are available to them. They will, for example, grasp objects placed in their hands, suck on objects that contact their mouths, and visually track moving objects. As infants apply these and other basic perception-action schemas to different objects and situations, they gradually adjust their action to the vast complexity of the world, increasingly accounting for specific objects and events. In the process, a more generalized and abstract sense of the world and infants' place in it emerges. By the end of infancy, the child has built a primitive understanding of objects and events as independently existing in time and space. For Piaget, a consequence of the infant period is an emerging representational ability, captured in the consolidation by eighteen to twenty-four months of an "object concept," which allows the child to conceive of an object's existence even when it is no longer available to the senses (e.g., out of view).

The study of representation in general—and the object concept in particular—has remained at the forefront of research in infant cognition. Examining infant search behavior, Piaget established six developmental stages through which infants pass before establishing a mature object concept. For example, during the third stage, around four to eight months, infants will search out a partially covered toy. But if the toy is completely hidden, infants will not search for it, as if it no longer exists. By the fourth stage, around eight to twelve months, infants will search for a completely covered toy, but when the toy is then hidden in another location, infants search exclusively at the initial hiding site, as if the toy's existence coincided with that particular location in space. More recent studies, using infant looking behavior, suggest that even younger infants have formed certain expectations about objects and their physical properties. For example, infants expect an object to stop moving when it contacts a solid barrier and expect that two inanimate objects must come in contact with one another for one object to set the other in motion. Young infants seem to apply these expectations even to events that occur out of view. When three-month-olds see a ball roll behind a screen, and then the screen is lifted to reveal a barrier to the ball's path, they look much longer, as if surprised, at the event when the ball is revealed resting at the other end of the barrier, having seemingly moved through the solid barrier. Whether these expectations constitute conceptual understanding of objects has been a source of debate.

Studies of infant imitation and memory have further contributed to the understanding of infant representational ability. Newborns will imitate the action of an adult sticking out his tongue, even though they cannot see themselves imitate the action. Some psychologists have argued that newborns must possess an abstract representational system for linking their unseen facial movements with what they see the adult doing. Around nine months, representation is clearly in place as infants, having only observed an adult play with a toy in a particular way, will imitate the adult when given a chance twenty-four hours later to play with the toy. In this deferred imitation, infants must represent what they have seen twenty-four hours earlier and must recall from memory the representation. Prior to nine months, infants can retain memories for weeks or even months, but they retrieve those memories only if sufficient cues are present to allow them to recognize the familiarity of an event.