Mental Work-load as a Function of Demand, Capacity, Strategy and Skill

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Abstract
An attempt is made to outline a conceptual framework in which to view the problems of defining and measuring mental work-load. This is treated in terms of the demands made by tasks, the capacities the subject brings to meet these demands, and the strategies he uses to relate the first to the second. Two types of demand are distinguished: the amount of data to be handled at a particular moment, and the amount to be dealt with during a particular period of time. Each type is considered in relation to the main central functions of perception, decision and choice, phasing and coordination of action, memory, and motivation. Capacity, and the effects of various factors upon it, are considered in relation to concepts of signal-to-noise ratio in the central nervous system. Three main types of strategy are outlined: coding and programming, methods of search, and balancing conflicting factors such as speed and accuracy or errors of omission and commission. Skill is discussed in terms of efficiency of strategy and a model is proposed to account for the attainment of skill with experience. Two basic approaches to the measurement of work-load are compared: the synthetic, in which the load imposed by the task as a whole is calculated from the loads imposed by its components; and the analytic, in which the task is studied as a whole, and components are analysed from the whole performance. Chronic stress and emotion are briefly discussed as long-term factors liable to affect work-load.