Working Memory’s Workload Capacity

We examined the role of dual-task interference in working memory using a novel dual 2-back task that requires a redundant-target response (i.e., that neither the auditory nor visual stimulus occurred two back vs. one or both occurred two back) on every trial. Comparisons with performance on single 2-back trials (i.e., with only auditory or only visual stimuli) showed dual-task demands reduced both speed and accuracy. Our task design enabled a novel application of Townsend and Nozawa’s (1995) workload-capacity measure, which revealed that the decrement in dual 2-back performance was mediated by sharing of a limited amount of processing capacity. Relative to most other single and dual n-back tasks, performance measures for our task were more reliable, due to the use of a small stimulus set that induced a high and constant level of proactive interference. For a version of our dual 2-back task that minimized response bias, accuracy was also more strongly correlated with a complex span than has been found for most other single and dual n-back tasks