passive element. We will begin to understand human-machine systems only when we begin to understand the adaptive interplay of practitioner and tools in the course of meeting task demands. Unfortunately, this demands, like Gibson demanded of the minimalist tachistoscopic school of work in perception, a paradigm shift for work on human-machine systems. It demands that researchers examine problem solving in situ -- in complex settings, in which significant information processing tools are available to support the practitioner and in which domain-knowledgeable people are the appropriate study participants ( Woods, 1993a).
The parallel to Gibson and ecological perception can be overdrawn with respect to the study of human-machine systems. The agent-environment mutuality assumption is (or should be) common to both endeavors. It is fairly easy to draw analogies between concepts in ecological perception and the ideas of some researchers in human-machine systems: the user as an active adaptive practitioner, the shift in the sense of what is informative, the search for meaning as a fundamental parameter in human-computer interaction, the need for a new way to characterize problem-solving habitats, the equivalent of an ecological physics, the multiplicity of cues available in natural problem-solving habitats, and the need to take into account the dynamism of real problems. But at another level the appeal of the term ecology of human-machine systems is based on the perceived need for a paradigm shift in human-machine systems -- a parallel to the Gibsonian paradigm shift in research on perception and action. The paradigm shift is an abandonment of the context-free approach and methods in the study of human-machine systems and a commitment to the methods and agenda of a context- bound approach.