Jean Piaget, the 19th- and 20th-century Swiss philosopher and psychologist, developed a well-noted cognitive theory of child development. Piaget’s theory incorporated linguistic and conceptual development, mathematical and scientific reasoning, and moral development into a theory that explained how infants and children think. Piaget postulated that four different stages of cognitive development exist in children and adolescents, the first of which covered birth to 2 years. He called this the sensorimotor stage, although now people sometimes refer to this as the sensory-motor stage.
Piaget developed four stages of cognitive development in a child. The first stage is the sensorimotor stage, which happens from birth to 2 years. In this stage, the infant is born with reflexes, but as he progresses through infancy, he begins to seek sensation. He then develops object permanence, in which he knows that an object exists even if he cannot see the object. The second stage is the preoperational stage, which happens between ages 2 and 7. In this stage, the child classifies objects in simple ways by physical features rather than in abstract or conceptual ways. The third stage is the concrete operations stage, which happens between ages 7 and 12. In this stage, the child begins to think abstractly and to conceptualize. The fourth stage is the formal operations stage, which begins at age 12 and continues through the end of childhood. In this stage, the child will be able to make decisions based on deductive and hypothetical reasoning, and his abstract thinking is very similar to that of an adult’s.
During the sensorimotor stage, but not beyond, infants perform certain motor-based reflexes. Parents will see newborns show the rooting reflex, in which babies turn their heads to the side and open their mouths after a parent or caretaker has stroked a baby’s cheek or mouth. This helps infants with feeding, as does the sucking reflex. When the roof of a newborn's mouth is touched, she will begin sucking. Newborns should also have the Moro reflex (sometimes known as the startle reflex), which causes newborns to throw their heads back, push out their arms and legs, and to cry when startled. Parents should also expect to see the Babinski reflex, in which the big toe bends toward the top of the foot and the other toes fan out after a parent or caretaker has firmly stroked the sole of the foot.
Though newborns love cuddling, it is not until around 4 months old that infants start seeking sensation. During this stage, infants learn to repeat actions that give them pleasure. A parent might see her infant accidentally stick her thumb in her mouth, and then see the infant repeat the action because sucking her thumb felt pleasurable. As an infant moves toward her first birthday, she gets better at deliberately searching for and finding positive sensations. At 5 months old, an infant might cuddle a soft blanket you give her; at 10 months old, an infant will crawl across the room to cuddle her favorite stuffed animal.
Object permanence also develops during infancy. When infants have reached this stage, they understand that just because an object disappears does not mean that the object has ceased to exist. A 4 month old will not look for a toy his parents hid. If the infant cannot see the toy, it ceases to exist for him. However, somewhere between 8 and 12 months old, a normally developing infant will start looking for the toy his parents hid. He will understand that the toy did not disappear but that it still exists. This is important because an infant who has reached the stage of object permanence knows that when his mother leaves his side and goes to the next room that his mother did not disappear but that she is somewhere – just not at his side.