Mechanisms of visual-spatial attention: resource allocation or uncertainty reduction?

Many studies have found that stimuli can be discriminated more accurately at attended locations than at unattended locations, and such results have typically been taken as evidence for the hypothesis that attention operates by allocating limited perceptual processing resources to attended locations. An alternative proposal, however, is that attention acts to reduce uncertainty about target location, thereby increasing accuracy by decreasing the number of noise sources. To distinguish between these alternatives, we conducted 6 spatial cuing experiments in which target location uncertainty was eliminated. Despite the absence of uncertainty, target discriminations were more accurate at the attended location, consistent with resource allocation models. These cue validity effects were observed under a broad range of conditions, including central and peripheral cuing, but were absent at very short cue-target delay intervals.