Jean Piaget, Swiss cognitive theorist (his doctorate was in Biology), put forth a highly influential framework of child development which is well-respected in education to this day. His developmental stages are predicated upon the idea that children mature into readiness for learning and thinking tasks in a predictable pattern. The first stage, called Sensorimotor, is comprised of infancy through age two, and is divided into six substages based upon age. The primary cognitive relationship during this stage is the interaction of the infant with her environment through the medium of action. Piaget's theory is based upon his assertion that "to know an object is to act upon it" which he terms "operation in his paper Development and Learning.
Infants are in the first substage of Piaget's Sensorimotor Development from birth to one month of age. During this time, innate reflexes are manifested. At the beginning of this stage, your baby grasps whatever is placed in her palm--your finger, a lock of your hair. Infants begin to adapt these reflexes to voluntary movement as age approaches one month. At this point he no longer relies on a simple grasping reflex but begins to exercise choice.
Between one and four months of age, your baby becomes aware of objects through his senses. He begins to discriminate, preferring, for example, the scent of his mother over the scent of a stranger. Motor movement at this stage is egocentric, meaning that it is focused on the baby's own body and comfort. Object permanence has not developed. For example, if you show your baby a bright toy or pacifier and then move it out of his field of vision, it simply goes away in his perception, ceasing to exist.
Object Permanence and Imitation
As your baby reaches sub-stage three, from four to eight months old, she will come to understand that objects you hide or take away will come back because they still exist. Peek-a-boo is a big hit during this stage. She will imitate you now, especially facial expressions and waving. Repetition will be very popular for your baby as she is enjoying a new stage of capability and can do a great deal more than she could previously. Playtime is a favorite during the object permanence stage.
As your baby nears one year old, he enters substage four. He will hunt for a hidden object, knowing that it still exists and seeking it out. He is now able to see that actions cause things to happen such as the fact that throwing a toy into the floor from his high chair puts it out of his reach. He will begin to set goals such as finding a hidden toy or imitating your actions and movements to be like you. This is the beginning of goal directed behavior, which occurs between eight and twelve months of age.
From ages twelve to eighteen months, your baby becomes more mobile and curious. She experiments with new objects and movements and may put everything she finds into her mouth. As she explores, she figures out how to make toys work and how to make noises by banging on things. While still largely nonverbal, she finds ways to communicate with those around her and learns to see people as agents of cause, meaning that she can get them to do things and bring her things. A tiny tyrant at this stage, your baby is figuring out how to perform early operations on her surroundings to achieve a goal.
Between eighteen and twenty-four months of age, your infant is in the final substage of Piaget's sensorimotor development. She begins to make sounds and say words spontaneously. She has a memory bank of imitations and actions that she can call forth and do without being prompted. She may delay imitating you when you want her to make a certain face or say a particular word--making you wait. She will now get creative and develop strategies to get what she wants--this often involves climbing. Much more sophisticated in her thinking now, your baby will make and execute plans now.