This chapter presents three premises of an ecological approach to human-machine systems. The first premise is that human-machine systems are dynamic, closed-loop systems that require a circular view of causality. The second premise is that the behaviour of these dynamic systems can best be understood in terms of the constraints in the functional workspace. These constraints include design intentions (e.g., functional goals), physical laws, organizational structure, and physical process and form. The final premise is that the explicit representation of the workspace constraints in the interface will greatly facilitate performance and will enhance the overall stability of the human-machine system.
Despite incredible advances in the development of automated control systems that are capable of closing many of the inner loops in complex work domains (e.g., energy production, advanced manufacturing, or aviation) human operators are ultimately responsible for controlling these work processes. That is, a human operator must monitor the system, compare the state of the system to normative expectations and functional objectives, and ultimately intervene in a way that will compensate for any deviations that are observed. At some level (more likely at multiple levels) the loop is closed through one or more human operators. Thus, stability of the system depends, in part, on the humans’ ability to perceive deviations and to act appropriately to correct those deviations. Thus, whenever a system breaks down, it will almost always be possible to trace back and find that human actions were on the error path. That is, the human made an incorrect action, failed to detect a significant deviation, or failed to diagnose the deviation (i.e., correctly compensate for the deviation). Thus, it is tempting to identify human error as the “cause” in many accidents. However, since error trajectories are often unique, it is difficult, based on analysis of the time histories (causal trajectories) of these events, to draw general principles that will help in the design of safer systems. An ecological approach attempts to take a broader holistic view that looks beyond activities (behavioural trajectories) to consider the landscape (i.e., ecology) that shapes trajectories within a work domain.
This chapter will consider some of the premises that motivate an ecological approach to the analysis of work domains and to the design of interfaces. The chapter is organized into three major sections. The first section considers the nature of the coupling between perception and action. The second section discusses the identification of constraints as a fundamental goal of analysis and as the semantic foundation for building interfaces. The third section discusses the specification of constraints within representations as a critical factor for skilled control.
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