Analysis Techniques For Man-Machine Systems Design
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Analysis Techniques For Man-Machine Systems Design

Analysis Techniques For Man-Machine Systems Design Analysis Techniques For Man-Machine Systems Design

ai.eecs.umich.edu
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11.07.2015 Views

NATO UNCLASSIFIEDAC/243(Panel 8)TR/7 - 88 -Volume 2on the measurement of subjective workload to verify that system performance requirements will be met. As noted inVolume 1, detailed considerations of the use of prototyping, simulation and field trials are outside the scope of thisreview. The links between analytical techniques and other approaches are discussed where possible.human tasks & task sequences,pacing times &events. & performance requirements4 -task tasks associate with high/ow tmes or erormanceanalysisredictinpf noperatoreoper \ act ignsequene \ acins \ tms/ features/Of tsks \ dictated by byh/diaeytaskF inputs & R a the between operato macoutputs, timesd o inte rface ad wo pormace d ifrequencies,\\ //performancerequirements6 -A variety of approaches are -available -to predict operator performance analytically (Meister. 1985). Most of them usethe concept of operator "workload" rather than a measure of performance itself (Hart & Wickens, 1990). Someestablished techniques such as the time Line analysis of workload (5.1) are normative, based on a single task analysissequence. Network simulations of operator tasks, such as PERT. SAINT and MicroSAINT (5.2) can be madestochastic so that the external mission events, and the task times and sequences, are drawn from a distribution oftimes and probabilities. Network simulations can link workload to system performance because they can produceestimates of task success in terms of percentage of tasks completed. or time to complete, using models of humanperformance, as well as producing estimates of operator workload (Chubb, Laughery & Pritsker, 1987). NATOAC/243 Panel 8/RSG.9 has reviewed and reported on those techniques and on a variety of models of humanperformance (McMillan et al., 1989, 1991). One specific approach, SIMWAM (5.3) is included here, because of theextensive use made of it for weapon systems development.Performance predictions can also be made using subjective workload measurement techniques (5.4). For example,although the SWAT technique (5.5) was developed for the evaluation of an existing, or simulated, system, it can beapplied pomjecavely (Pa-SWAT) to the prediction of operator workload based on a task analysis. The NASA TaskLoad Index (TLX) (5.6) can be applied projectively also.In following either a simulation modelling approach or a subjective workload approach to predicting operatorperformance, it must be remembered that the relationship between workload and performance is not straightforward.As task demands vary with time, the operators may increase or decrease their effort to compensate, or their effort maydecline due to fatigue (Fig. 5.2). Thus at the outset of a mission, the task demand may lie within an operator'sNATO UNCLASSIFIED- 88 -

NATO UNCLASSIFIED- 89 - AC/243(Panel-8)TR/7Volume 21 iniscapability, whereas at the end of a mission, the same level of task demand may exceed the operator's capability. Hart& Wickens,.(1990) discuss the Performance Resource Functions (PRF) which relate workload, performance, andoperator effort in different situations.-AC c v ~pilot capability-0.;efell tactical fligh ,en-routetransittake-offapproach & landingmission task demandsTime -At point A, pilot capability exceecs mission task demands by 25%At point B. pilot capability barely exceeds same level of task demandsFigure 5.2: Example of the relationship between mission task demandsand operator capability (after Tepper & Haakanson, 1978);e Error analysis is another aspect of performance prediction. A variety of approaches have been taken to error analysis(Lepiat et al., 1990; Rasmussen, Duncan & Lcplac, 1987). Some approaches use fault tree analysis or failure modeseffects analysis to identify those operator actions which could result in a system-critical incident or situaion. TheTechnique for Human Error Prediction (THERP) reviewed by NATO AC/243 Panel-8/RSG.9 (McMillan et al.,1991), is the most well known example. Other approaches attempt to identify design features which are associatedwith human error. In that context, many of the established human engineering design recommendations are intendedto control "design induced error." Woodson (1981) provides examples of lists of quantitative and qualitativeapproaches to analysing designs for human error. It should be noted, however, that the whole subject of operator erroris a contentious one. There are many problems with the definition and classification of human error. For example,error is context dependent and accident and incident analysis require value judgements to be made (Ridley, 1991).Because of such problems, only a simple generic approach to error analysis based on actual application is reviewedhere (5.7). The prediction of human error requires a data base for associated probabilities of occurrence. An approachwhich has been applied to the collection of data from accidents is also reviewed (5.8).IyNATO UNCLASSIFIED- 99 -

NATO UNCLASSIFIED- 89 - AC/243(Panel-8)TR/7Volume 21 iniscapability, whereas at the end of a mission, the same level of task demand may exceed the operator's capability. Hart& Wickens,.(1990) discuss the Performance Resource Functions (PRF) which relate workload, performance, andoperator effort in different situations.-AC c v ~pilot capability-0.;efell tactical fligh ,en-routetransittake-offapproach & landingmission task demandsTime -At point A, pilot capability exceecs mission task demands by 25%At point B. pilot capability barely exceeds same level of task demandsFigure 5.2: Example of the relationship between mission task demandsand operator capability (after Tepper & Haakanson, 1978);e Error analysis is another aspect of performance prediction. A variety of approaches have been taken to error analysis(Lepiat et al., 1990; Rasmussen, Duncan & Lcplac, 1987). Some approaches use fault tree analysis or failure modeseffects analysis to identify those operator actions which could result in a system-critical incident or situaion. TheTechnique for Human Error Prediction (THERP) reviewed by NATO AC/243 Panel-8/RSG.9 (McMillan et al.,1991), is the most well known example. Other approaches attempt to identify design features which are associatedwith human error. In that context, many of the established human engineering design recommendations are intendedto control "design induced error." Woodson (1981) provides examples of lists of quantitative and qualitativeapproaches to analysing designs for human error. It should be noted, however, that the whole subject of operator erroris a contentious one. There are many problems with the definition and classification of human error. <strong>For</strong> example,error is context dependent and accident and incident analysis require value judgements to be made (Ridley, 1991).Because of such problems, only a simple generic approach to error analysis based on actual application is reviewedhere (5.7). The prediction of human error requires a data base for associated probabilities of occurrence. An approachwhich has been applied to the collection of data from accidents is also reviewed (5.8).IyNATO UNCLASSIFIED- 99 -

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