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There appear to be three independent systems for allocating attention: space-based, feature based, and object-based. Here, we review the literature of object-based attention to determine its underlying mechanisms. First, findings from unconscious priming and cuing suggest that the pre-attentive targets of object-based attention can be fully developed object representations. Next, the control of object-based attention appears to come from ventral visual areas specialized in object analysis that project downward to early visual areas. Whether feedback from object areas can accurately target the object’s specific locations and features is controversial, but recent work in autoencoding has made this plausible. Finally, we suggest that the three classic modes of attention may not be as independent as is commonly considered, and instead could rely on object-based attention for all three modes of selection. Specifically, studies show that attention can spread over the separated members of a group – without affecting the space between them — matching the defining property of feature-based attention. At the same time, object-based attention directed to a single small item has the properties of space-based attention. Nevertheless, the evidence for a parallel, space-based selection controlled through saccade centers is also convincing. We outline the architecture for this combined system and discuss how it works in parallel with other attention pathways.

When a part of an object is cued, targets presented in other locations on the same object are detected more rapidly and accurately than are targets on other objects. Often in object-based attention experiments, cues and targets appear not only on the same object but also on the same surface. In four psychophysical experiments, we examined whether the "object" of attentional selection was the entire object or one of its surfaces. In Experiment 1, facilitation effects were found for targets on uncued, adjacent surfaces on the same object, even when the cued and uncued surfaces were oriented differently in depth. This suggests that the "object-based" benefits of attention are not restricted to individual surfaces. Experiments 2a and 2b examined the interaction of perceptual grouping and object-based attention. In both experiments, cuing benefits extended across objects when the surfaces of those objects could be grouped, but the effects were not as strong as in Experiment 1, where the surfaces belonged to the same object. The cuing effect was strengthened in Experiment 3 by connecting the cued and target surfaces with an intermediate surface, making them appear to all belong to the same object. Together, the experiments suggest that the objects of attention do not necessarily map onto discrete physical objects defined by bounded surfaces. Instead, attentional selection can be allocated to perceptual groups of surfaces and objects in the same way as it can to a location or to groups of features that define a single object.

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Have you ever searched the pages of a Where’s Waldo® book and found it difficult to find him? Your eyes jump around the page scanning for his red-and-white striped shirt, but all you seem to find are other funny characters. Maybe you keep getting distracted by a big green monster that does not look anything like Waldo. After you finally find him, you realize that you looked right at Waldo many times without noticing him. Do not worry! In this article, we explain that this is not because you are a bad detective, but because of the way the brain works when we pay attention.