Cognized environment is a concept first introduced by the late anthropologist Roy Rappaport (1968), in contrast to what he called the operational environment (see Rappaport 1979:97-144, 1984:337-352). Rappaport was an ecological anthropologist, like Andrew P. Vayda, and wished to contrast the actual reality and adaptations (the operational environment) within a people's ecological niche – say, the existence of tsetse flies and their role in causing sleeping sickness among humans – with how the people’s culture understands nature (the cognized environment) – say, the belief that witches live in those areas that science knows is the habitat of the tsetse. Rappaport’s principal concern was the role of ritual in mediating the cognized and operational environments.