Abstract
In addition to attending to continuous regions of space, we also attend to discrete visual objects. A foundational result in this domain is that attention "spreads" within an object: If we attend to one portion of an object, we can't help but attend to the rest of it, as revealed by facilitated probe detection for other within-object locations. But what can be the objects of object-based attention? In particular, is this process limited only to the here and now, or can we also attend to objects that don't yet exist but merely *could* exist at some future time? Here, we explore how attention spreads not only to other locations within a single, present object, but also to disconnected object-parts that could combine with a presently attended object to create a new object. We designed stimulus triplets consisting of one puzzle-piece-like central shape and two nearby puzzle-piece-like shapes, one of which could neatly combine with the central shape and one of which could not (as determined by the presence of certain protrusions and indentations). Shortly after stimulus onset, two letters appeared, one on the central shape and another on one of the two smaller parts: either the "combinable" piece or the "non-combinable" piece. Subjects simply decided whether the two letters were the same or different. We found that subjects were faster to evaluate letter-similarity when the two letters appeared on shapes that could combine into one, rather than on two shapes that could not — even without any differences in accuracy (ruling out a speed-accuracy tradeoff). Follow-up experiments ruled out mere similarity as a driver of this effect, isolating combinability per se. We suggest that attention can select not only actual objects that are present now, but also "possible" objects that may be present in the future.