Discrete resource allocation in visual working memory.

Are resources in visual working memory allocated in a continuous or a discrete fashion? On one hand, flexible resource models suggest that capacity is determined by a central resource pool that can be flexibly divided such that items of greater complexity receive a larger share of resources. On the other hand, if capacity in working memory is defined in terms of discrete storage "slots," then observers may be able to determine which items are assigned to a slot but not how resources are divided between stored items. To test these predictions, the authors manipulated the relative complexity of the items to be stored while holding the number items constant. Although mnemonic resolution declined when set size increased (Experiment 1), resolution for a given item was unaffected by large variations in the complexity of the other items to be stored when set size was held constant (Experiments 2-4). Thus, resources in visual working memory are distributed in a discrete slot-based fashion, even when interitem variations in complexity motivate an asymmetrical division of resources across items.