Cognitive development is a field of study in neuroscience and psychology focusing on a child's development in terms of information processing, conceptual resources, perceptual skill, language learning, and other aspects of brain development and cognitive psychology compared to an adult's point of view. In other words, cognitive development is the emergence of the ability to think and understand.[1] A large portion of research has gone into understanding how a child imagines the world. Jean Piaget was a major force in the establishment of this field, forming his "theory of cognitive development". Piaget proposed four stages of cognitive development: the sensorimotor, preoperational, concrete operational and formal operational period.[2] Many of his theoretical claims have since fallen out of favor. However, his description of the more prominent changes in cognition with age (e.g., that it moves from being dependent on actions and perception in infancy to an understanding of the more observable aspects of reality in childhood to capturing the underlying abstract rules and principles in adolescence) is generally still accepted today. Perhaps equally importantly, Piaget identified and described many cognitive changes that must be explained, such as object permanence in infancy and the understanding of logical relations and cause-effect reasoning in school age children. The many phenomena he described still attract the interest of many current researchers.In recent years however, alternative models have been advanced, including information-processing theory, neo-Piagetian theories of cognitive development, which aim to integrate Piaget's ideas with more recent models and concepts in developmental and cognitive science, theoretical cognitive neuroscience, and social-constructivist approaches.A major controversy in cognitive development has been "nature versus nurture", that is, the question if cognitive development is mainly determined by an individual's innate qualities ("nature"), or by their personal experiences ("nurture"). However, it is now recognized by most experts that this is a false dichotomy: there is overwhelming evidence from biological and behavioral sciences that from the earliest points in development, gene activity interacts with events and experiences in the environment.[3]