The ecological approach owes much to the thinking of Gibson (1950, 1966, 1979). From the ecological perspective, the activities of an individual are assumed to always be constrained by an interaction between the individual’s capabilities and the properties of the environment that envelops that individual. In order to understand the individual’s activities and to design artifacts that meet the individual’s needs, it is necessary to understand the ways in which that individual’s capabilities interact with the surrounding environment. From an ecological perspective, the individual and his or her environment is conceived of as an inseparable pair, in the sense that one cannot be defined, let alone understood, without reference to the other. It is easy to appreciate the fact that the individual simply could not exist without an environment, but it is equally true, although perhaps not as obvious, that the environment, insofar as it exists as a niche for a specific individual, could not be defined without the individual that it environs or surrounds (Gibson, 1979).