Location-based effects underlie feature conjunction benefits in visual working memory

Studies of visual working memory (VWM) have reported that different features belonging to the same object (conjunctions) are better retained than the same features belonging to spatially separated objects (disjunctions). This conjunction benefit has been taken as evidence for the theory that VWM representations are object-based. However, compared to separate features, conjunctions also occupy fewer locations. Here we tested the alternative hypothesis that the conjunction benefit reflects a spatial-based rather than an object-based advantage. Experiment 1 shows a clear VWM conjunction benefit for spatially laid out displays of memory items. However, when the same items were presented sequentially at one location (i.e., location was noninformative), memory performance was equivalent for conjunction and disjunction conditions. Experiment 2 shows that only when the probe carries spatial information (i.e., it matches the location of the memory item) does a conjunction benefit occur. Taken together, these results put important boundaries on object-based theories of VWM.