On data-limited and resource-limited processes

This paper analyzes the effect on performance when several active processes compete for limited processing resources. The principles discussed show that conclusions about the interactions among psychological processes must be made with caution, and some existing assumptions may be unwarranted. When two (or more) processes use the same resources at the same time, they may both interfere with one another, neither may interfere with the other, or one may interfere with a second without any interference from the second process to the first. The important principles are that a process can be limited in its performance either by limits in the amount of available processing resources (such as memory or processing effort) or by limits in the quality of the data available to it. Competition among processes can affect a resource-limited process, but not a data-limited one. If a process continually makes preliminary results available even before it has completed all its operations, then it is possible to compute performance-resource operating characteristics that show how processes interact. A number of experiments from the psychological literature are examined according to these processing principles, resulting in some new interpretations of interactions among competing psychological processes.