Maintenance of Bound or Independent Features in Visual Working Memory is Task-dependent

Conflicting findings exist regarding whether features of an object are stored separately or bound together in visual working memory. This controversy is based on an implicit assumption about a default, or fixed, mode of working memory storage. In contrast, here we asked whether the anticipated task might determine the format in which information is maintained in working memory, consistent with its task-oriented function. To test this flexible maintenance hypothesis, we recorded EEG while subjects performed a delayed (Yes/No) recognition task with different requirements and loads. Across three experiments, we compared event-related potentials (ERPs) in conditions with and without the necessity of maintaining conjunctions between features, while controlling for differences in visual stimulation. In Experiment 1 (N=24), involving color-location conjunctions, we identified a delay-period effect characterized by a positive potential shift in central-parietal channels when conjunction was not required by the task. This pattern, distinct from the effect caused by an increased working memory load, was confirmed in Experiment 2 (N=23) with an independent group of subjects using a similar paradigm, while also controlling for the physical appearance of probes. Finally, the observation of color and location conjunction in Experiments 1 and 2 was extended to Color and Orientation conjunction in Experiment 3 (N=22). Collectively, these three experiments provided reliable evidence demonstrating that the maintenance of feature conjunctions in working memory, whether spatial (location) or non-spatial (non-location), depends on the task goal.