Usability Questionnaire Results - Institute of Aviation - University of ...

complexity of the power system and its real time dynamics while dealing with high levels ofworkload.Moray (1997) sums up many of the human factors challenges that occur in processcontrol. Some of these include designing control rooms to support safe and economic operation,shifting from physical skills to cognitive skills due to increased use of automation (supportingdecision making), the design and evaluation of advanced interfaces, and the identification of agood balance between prescribed activities and creative intervention.One important role of operators in a process control system is to monitor the state of thesystem. Operators have a particular interest in detecting faults within a system and being able todiagnose the underlying cause of the failures. These two important tasks will be examined in thecontext of process control.2.1.1 DetectionThe detection of abnormal and fault conditions in a process control setting such asnuclear power or power systems is often a complex and difficult task. Detection of faults inprocess control is guided by research in signal detection (Green & Swets, 1966; Swets & Pickett,1982; Wickens & Hollands, 2000) and vigilance (Mackworth, 1948; Davies & Parasuraman,1982; Wickens & Hollands, 2000). Signal detection in its most basic terms consists of twostages: Collecting evidence as to whether a signal is present or absent, and then making adecision about whether the evidence indicates a signal or not. Four outcomes result from signaldetection. A hit indicates that a signal was correctly indicated, a miss means that a signal wasnot indicated, a false alarm indicates a signal was detected when in fact there was none, and acorrect rejection means a signal was not indicated when there was not a signal. Factors affectingsignal detection include sensitivity (the level of discriminability of the signal from noise) and theresponse bias (conservative vs. risky strategy). An example of response bias can be seen bylooking at a nuclear power plant operator. An operator monitoring a nuclear power plant wouldwant to catch all faults that occur due to the severe consequences of missing a failure. Therefore,the operator may have a more liberal response bias and detect more false alarms while detectingmost failures.In the control of power systems, operators may have different response biases dependingon their tasks or instructions. If an operator who monitors a power system has been told by asupervisor not to shut down portions of a grid unnecessarily since it can be quite costly, theoperator may be more conservative when detecting power grid faults and therefore not catch asmany faults. The basis of the research on vigilance has found that the ability to detect signalsdecreases over time, and the steady-state level of detecting signals in vigilance tasks is less thandesirable.Key differences exist from the detection in simulated environments of the classic researchexperiments and process control environments (Wickens & Hollands, 2000). Operators inprocess control do not wait passively for failures but instead are engaged in other monitoring andcontrol tasks (Moray & Rotenberg, 1989). This means that arousal can be maintained and thisreduces the vigilance decrement. Second, failures in process control are normally accompaniedby alarms. This provides a salient feature that draws operator’s attention and aids detection.7