Final answer:
Object permanence is the understanding that objects continue to exist even when not perceived, while egocentrism is the belief that everyone thinks as you do. Object permanence develops in the sensorimotor stage, whereas egocentrism is characteristic of the preoperational stage.
Step-by-step explanation:
The concept in question is object permanence, which is the understanding that objects continue to exist even when they are not visible. Research by developmental psychologist Jean Piaget demonstrated that very young children do not show object permanence, which is a hallmark of the sensorimotor stage of development. By contrast, egocentrism is a characteristic of the preoperational stage, where children are unable to take the perspective of others and believe that everyone sees and thinks as they do. As they grow older and transition through later stages of cognitive development, children overcome egocentrism and develop a more refined understanding of others' perspectives, a concept known as theory of mind (TOM).