Do mental processes share a domain-general resource?

What determines success and failure in dual-task situations? Many theories propose that the extent to which two activities can be performed concurrently depends on the nature of the information involved in the activities. In particular, verbal and visuospatial activities are thought to be fueled by distinct resources, so that interference occurs between two verbal activities or two visuospatial activities, but little or no interference occurs between verbal and visuospatial activities. The current study examined trade-offs in four dual-task situations in which participants maintained verbal or visuospatial information while concurrently processing either verbal or visuospatial information. We manipulated the cognitive load of concurrent processing and assessed recall performance in each condition. Results revealed that both verbal and visuospatial recall performance decreased as a direct function of increasing cognitive load, regardless of the nature of the information concurrently processed. The observed trade-offs suggest strongly that verbal and visuospatial activities compete for a common domain-general pool of resources.