Regarded as the foremost developmental psychologist of the 20th century, Piaget developed a theory of “genetic epistemology,” a natural timetable for the development of the child’s ability to think, in which he traced four stages—the sensorimotor (ages 0–2), preoperational or symbolic (2–7), concrete operational (7–12), and formal operational (12 and up)—each marked by increased cognitive sophistication and ability to use symbols. What specific developments occur in each stage? Discuss