Abstract
Working memory is commonly understood as consisting of two distinct sub-systems: a ‘visuospatial sketchpad’ and a ‘phonological loop’. Studies of visual working memory often deliberately ignore the phonological loop, using stimuli that cannot be easily verbally encoded (e.g., oriented lines). But how do these two seemingly distinct systems interact? Here, we ask whether (and how) task-irrelevant spatial structure influences working memory. Observers were introduced to a novel working memory task in which they saw a series of 5-7 shapes that appeared (a) in one of four colors and (b) in one of four locations (quadrants). They were explicitly told that they had to recall only (a) the shapes that they saw and (b) the order they saw them in — not color or location. On some trials, space was structured so that any shape appearing multiple times appeared in the same location and no other shape appeared in that location (whilst color was randomized); on other trials, color was structured (whilst location was randomized). This task therefore had two key components: (1) both color and location information were task-irrelevant; (2) the to-be-remembered information (shape names) could be rehearsed. Despite this (and frequent participant reports of a rehearsal strategy), we observed a robust memory advantage in the space-structured condition. We replicate this general pattern across several experiments, and further show that these findings (a) should be understood as a space-advantage rather than a color-decrement, and (b) this benefit occurs because of the consistency for location within object (rather than the lack of overlap between objects). In other words, it appears that spatial information (ostensibly invoking the ‘visuospatial sketchpad’) benefits working memory, even when observers explicitly use a rehearsal strategy — suggesting a prioritization of spatial information. These findings also address how task-irrelevant spatial information influences working memory in the first place.