ABSTRACT
This chapter argues that both person and task concepts of effort are equally relevant to both single- and dual-task performance, a distinction made. Thus, even without direct measurement of human performance it is possible to predict the level of resource demand of some of these tasks. The secondary-task approach is based on the simple reasoning that if the primary task requires fewer resources, it will avail more resources for the secondary task, performance of which will increase accordingly. The resource demand, or difficulty, of a task is intuitive and is a strong predictor in accounting for differences in the success of divided attention, or time sharing, between tasks. The general framework for considering effort in a single-task context is that the investment of excessive mental effort, excessive physical effort, generally produces an unpleasant state that is to be avoided. The effort-saving benefit of this heuristic will grow, as the choice space expands to include both more options and more attributes.
