One of the main contributors to the cognitive perspective are psychologists Jean Piaget, Piaget develops the theory of cognitive development and the stages of cognitive development. Overall, the cognitive perspective is based on internal mental states that behaviorists simply ignore. For example, internal states include confidence, desires, thoughts, and inspiration. Although internal mental states cannot observe any behavior, but they can obtain information that is perceived, processed, stored, retrieved and forgotten and includes perception, categorization, memory, knowledge representation, language and thinking