Visual attention, the mechanism by which observers select relevant or important information from scenes, can be deployed to locations in space or to spatially invariant object representations. Studies have examined both the modulatory effects of attention on the strength of extrastriate cortical representations, and the control of attention by parietal and frontal cortical circuits. Subregions of parietal and frontal cortex are transiently active when attention is voluntarily shifted between spatial locations or object representations. This transient activity may reflect an abrupt shift in the attentional set of the observer, complementing sustained signals that are thought to maintain a given attentive state.