According to Piaget, the first responses that infants make in the world occur by chance, so infants discover the reponses that they can perform by chance. Shortly after this period, children will begin experimenting with new ways of doing things that will satisfy their curiousity. The result of that experimentation will be that children develop an ability for inner experimentation, where they can perform an activity in their head before doing it in the world. Others have suggested that the ability to perform deferred imitation appears earlier. There is evidence that 14 month olds can imitate the actions of live models as much as a week after seeing them.
Object permanence is also a part of the sensorimotor stage.
Object permanence is the idea that an object is permanently in the world, even if it is removed from view. Infants start out believing that objects placed out of sight are out of existence, and gradually acquire the belief that out of sight does not mean out of this world. Infants start life as egocentrics, as they are unable to think of another person's point of view. This egocentrism can explain why children may appear selfish, as they are unable to think of others viewpoint. The notion of egocentrism is related to the idea of whether children can think symbolically.