Describe the four stages in Piaget's theory of cognitive development.What major milestones are achieved at each stage?

Piaget's first stage, the sensorimotor stage, lasts from birth to about 2 years of age.In this stage, infants construct an understanding of the world by coordinating sensory experiences with motor actions.Object permanence, the understanding that objects and events continue to exist even when they cannot directly be seen, heard, or touched, is the major milestone that is achieved toward the end of the sensorimotor stage.Piaget's second stage of cognitive evelopment, the preoperational stage, lasts from approximately 2 to 7 years of age.Preoperational thought is more symbolic than sensorimotor thought.In preschool years, children begin to represent their world with words, images, and drawings.Thus, although their thoughts begin to exceed simple connections of sensorimotor information and physical action, preoperational thought is intuitive and egocentric.Symbolic thought is the major milestone achieved in the prepoperational stage.Piaget's concrete operational stage (7 to 11 years of age) involves using operations and replacing intuitive reasoning with logical reasoning in concrete situations.Children in the concrete operational stage can successfully complete conservation tasks.Individuals enter the formal operational stage of cognitive development at 11 to 15 years of age.This stage continues through the adult years.Formal operational thought is more abstract and logical than concrete operational thought.The ability to engage in hypothetical-deductive reasoning is a major milestone of formal operational thought.