ABSTRACT
The effect of task difficulty on dual-task performance is conceptualized within two alternative theoretical frameworks: One posits that performance depends on the use of resources from a common pool; the other views the processing system as comprised of a number of mechanisms, each having its own capacity that may be considered as a separate resource. It is shown that under the central capacity model difficulty should most often interact with resource investment in such a way that effects of resource investment on quality or speed of performance are more pronounced the easier the task is. The implication of this result to performance in dual-task situations is discussed. If multiple resources are assumed, then a difficulty manipulation may differentially affect the use of each of those resources. If in a dual-task situation a manipulation of the difficulty of one task affects the use of a mechanism that is not required by the other task, processing of the latter may remain intact in some circumstances. To obtain a complete picture of how difficulty affects dual-task performance, it is proposed to manipulate task priorities as well as difficulty parameters and to present their joint effect by families of performance operating characteristics. An application of this approach to the study of pursuit tracking is briefly described and interpreted in terms of the multiple resources approach.
