On the Economy of the Human Processing System: A Model of Multiple Capacity.

Abstract

An approach to human performance which is based on economic concepts is proposed. This approach hinges on the idea that the human processing system has a number of mechanisms each having its own capacity. Those capacities can at any moment be allocated among several processes. Since tasks may differ with respect to the types of mechanisms they call for and the demands they pose for the use of those mechanisms, it is argued that the hope to find single measures for system capacity and mental load may be groundless. Different pairs of time-shared tasks may conflict with each other to a variable degree, which is difficult to predict without knowing the overlap in their demand for various mechanisms. The amount and specific nature of trade-off between time-shared tasks can be displayed by means of performance operating characteristics. The effects of a number of properties of the system and of the tasks on the shape and interpretation of performance operating characteristics are discussed. The analysis in this paper also serves to elucidate the notion of resources brought forward by previous authors, to elaborate on the distinction between demand for and supply of resources, to discuss possible interactions between the effects of supply of resources and situation parameters on performance, and to conjecture about the way by which allocation policy depends on the value of outcomes of different allocations.