A general framework is outlined for describing the relationship of cognition to brain systems. The model provides for empirical investigations at many levels--computational, chronometric, spatial imaging, and cellular--and argues for the logical interrelationship of these areas of investigation. It is applied to selective visual-spatial attention studies in which specific cognitive operations have been related to regional neural systems, by studying brain-injured patients. Studies with alert monkeys are also discussed. Studies of cross-modality cuing and interference suggest that the parietal system is also related to spatial orienting, irrespective of modality and type of cue. Thus a hierarchical cognitive system of spatial attention results, in which somewhat separate modality-specific systems are organized. Patient studies suggest that spatial attention is a module within a more general system of attention that extends to other cognitive systems, such as language. While the anatomy of the more general system is unknown, the general framework does suggest the types of studies which may be useful in revealing its anatomical organization. (GDC)