Recent research has shown that an ecqlogical interface for a simulated pasteurization plant leads to most effective failure diagnosis pe?formance only if the interface is supported by an adequate set of sensors. In this investigation we examine the effect of interface on control performance, focusing especially on between-subjects variability in contiol actions taken and state variable values. Results provide some support for the idea that when the interface is supported by an adequate set of sensors, an ecological interface produces less between-subjects variability in the values of higher-order state variables, but more between-subjects variability in the number of control actions taken. We interpret these findings to indicate that when goals and higher-order properties of a system are revealed through effective interface design, the degrees of freedom for action at lower levels are more fullv exuloited, which is all the better to achieve the higher-order purposes of control. , A

This paper discusses the use of Rasmussen's abstraction hierarchy (AH) in performing an analysis of the work domain of a Pasteurization plant. Our goal is to examine the strengths and weakness of ecological interface design (EID) for systems in which critical variables are unreliable, faulty, or not measurable. In this paper we report our use of AHs to analyze the functioning of a pasteurization plant and the impact of unreliable or faulty sensors on the intelligibility of information available to the human operator. Although there is considerable current interest in EID, building thorough AHs for complex systems is a large task and there are currently very few detailed published examples to help human factors professionals wishing to take this approach. In this paper we present details of how we built the Pasteurization plant AH and show we are using the AH in our research. We argue that because AHs can indicate information that should be displayed for a process to be intelligible, techniques like EID that use AHs are in a position to bring about a profoundly user-centered approach to system design-an approach in which the ultimate information needs of human controllers will drive the engineering agenda of sensor and instrumentation design in a feedforward manner.

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In this paper we use sensor-annotated abstraction hierarchies (Reising & Sanderson, 1996, 2002a to show that unless appropriately instrumented, configural displays designed according to the principles of ecological interface design (EID) might be vulnerable to misinterpretation when sensors become unreliable or are unavailable. Building on foundations established in Reising and Sanderson (2002a) we use a pasteurization process control example to show how sensor-annotated AHs help the analyst determine the impact of different instrumentation engineering policies on a configural display that is part of an ecological interface. Our analyses suggest that configural displays showing higher-order properties of a system are especially vulnerable under some conservative instrumentation configurations. However, sensor-annotated AHs can be used to indicate where corrective instrumentation might be placed. We argue that if EID is to be effectively employed in the design of displays for complex systems, then the information needs of the human operator need to be considered while instrumentation requirements are being formulated. Rasmussen's abstraction hierarchy}and particularly its extension to the analysis of information captured by sensors and derived from sensors}may therefore be a useful adjunct to up-stream instrumentation design. #

Console operators in process plants have to maintain a high level of situation awareness to operate the plant safely, effectively, and efficiently. An overview display is one of the primary displays in a control room that operators monitor to gain and maintain an understanding of the plant. In this study, the authors evaluated operator performance using two overview display formats. The first format, characterized as a functional design, included qualitative, graphical indicators for process parameters and organized the position of the indicators on the basis of functional relations of the process equipment. The second format, characterized as a traditional schematic display, showed connecting process lines between equipment and numerical fields to present process information. Both displays contained the same indicator values. Eighteen plant operators used both display formats to monitor a crude unit process for process parameters that deviated from normal values. We measured operators' situation awareness using think-aloud protocols and situation awareness global assessment technique, subjective workload, and usability ratings. Results indicated that operators' situation awareness was significantly higher when they monitored the process on a functional display compared with a schematic display. Their subjective workload and usability ratings also favored the functional overview display format. Implications of the findings for continuous process control and overview display design are discussed.