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 the developed adult brain and cognitive psychology. Qualitative differences between how a child processes their waking experience and how an adult processes their waking experience are acknowledged (such as object permanence, the understanding of logical relations, and cause-effect reasoning in school-age children). Cognitive development is defined as the emergence of the ability to consciously cognize, understand, and articulate their understanding in adult terms. Cognitive development is how a person perceives, thinks, and gains understanding of their world through the relations of genetic and learning factors. There are four stages to cognitive information development. They are, reasoning, intelligence, language, and memory. These stages start when the baby is about 18 months old, they play with toys, listen to their parents speak, they watch tv, anything that catches their attention helps build their cognitive development. Jean Piaget was a major force establishing this field, forming his "theory of cognitive development". Piaget proposed four stages of cognitive development: the sensorimotor, preoperational, concrete operational, and formal operational period. Many of Piaget's theoretical claims have since fallen out of favor. His description of the most prominent changes in cognition with age, is generally still accepted today (e.g., how early perception moves from being dependent on concrete, external actions. Later, abstract understanding of observable aspects of reality can be captured; leading to the discovery of underlying abstract rules and principles, usually starting in adolescence) 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. Another such model of cognitive development is Bronfenbrenner's Ecological Systems Theory. A major controversy in cognitive development has been "nature versus nurture", i.e, 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. Early history Jean Piaget is inexorably linked to cognitive development as he was the first to systematically study