Behavioral studies of visual attention have suggested two complementary modes of selection. In a space-based mode, locations in the visual field are selected; in an object-based mode, organized chunks of visual information-roughly, objects-are selected, even if the objects overlap in space or are spatially discontinuous. Although the two modes are distinct, they can operate in concert to influence the allocation of attention. This chapter presents key experimental results on space-and

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... ed attention and their interaction, and sketches a theoretical framework in which the two attentional modes can be unified. This chapter also discusses alternative notions of objectbased attention, from perceptual grouping of low-level features in a retinotopic reference frame to construction of structural descriptions, and argues that the data are consistent with the former-a simple, low-level mechanism. Neurobiology of Attention