Are the limits in processing and storage capacity common? Exploring the additive and interactive effects of processing and storage load in working memory

Processing and storage constitute important aspects of working memory. However, the relationship between them remains unclear. If they constitute separate, independent capacities then manipulations of processing and storage load should have independent effects on task performance. In the present research, university students (N = 84) were administered a reasoning task based on the Greco-Latin square task, in which processing (as defined by relational complexity) and storage load were orthogonally manipulated. Theoretical processing and storage load were each able to predict significant unique portions of the variance in both item difficulty and correct response time. However, no interaction term was able to significantly increase predictive power for either item difficulty or correct response time. This suggests that over the range of processing and storage load imposed by the task, processing and storage capacity are largely additive (i.e., independent). Implications for models of working memory are discussed.