Jean Piaget proposed a comprehensive theory of child cognitive development identifying four major periods or stages of cognitive development the first of these stages the sensory motor stage spans the age range from birth to two years during the sensorimotor stage infants learned to coordinate sensory information and motor activity becoming increasingly able to act purposefully on their environments and solve problems at the beginning of the sensorimotor period and infants actions are confined to innate reflexes like sucking and grasping soon however infants will begin to show what Piaget called primary circular reactions one week old Aiden moves his hand near his mouth by chance in the next few weeks he will begin to try to reproduce this pleasurable experience eventually sucking his thumb or hand purposefully Jess apena who is two months old has learned that it is interesting to open and close her own hands near her face while primary circular reactions Center on a child's own body secondary circular reactions involve making interesting things happen in the world outside one's body by chance six week old Iceland causes the toy on the side of her bouncy seat to move but quickly figures out how to keep it going and five-month old James again by chance pushes a button on his toy and causes music to play after several attempts he is able to make the music start again at his own discretion [Music] unlike primary circular reactions secondary circular reactions are not based on reflexes but represent the first acquired adaptations of new behaviors at about eight months of age children show the first signs of planned intentional behavior nine month old Haydon for example drops one toy to grasp another oh you want to eat the Frog he also figures out how to move an obstacle the exersaucer to pick up a desired toy before this secondary reactions were executed for their own sake now Haydn has learned that one secondary circular reaction can be used in the service of another Haydn now uses two previously acquired schemes in coordination to achieve a goal dropping one toy to grasp another and moving an obstacle to retrieve a toy tertiary circular reactions occur between 12 and 18 months of age at this stage infants began to actively experiment with the world to do things just to see what will happen test for example tries a number of locations for the teething ring ending up wearing it as a bracelet the development of object permanence is one of the more notable cognitive changes occurring during the sensorimotor period children younger than about four months of age are unaware that objects continue to exist when they are no longer visible two month old Josefina does not even look for the toy when it is hidden between four and eight months however infants begin to retrieve objects that are partially hidden behind a barrier as six month old Anthony demonstrates by eight to twelve months infants begin to show clearer signs of object concepts consistently looking for objects when they are hidden Tess a 20 month old reaches right around a barrier to get to a toy showing as she has achieved object permanence being able to represent objects mentally is an important cognitive change as it allows children to think about things they can't see or touch using insight and mental experimentation for solving problems instead of trial and error