Directing spatial attention within an object: altering the functional equivalence of shape descriptions.

Three experiments extended the demonstrated effects of spatial attention to a new area, the perceptual organization of objects. We manipulated observers' fixation location, their spatial attention location, and their intentions to hold one alternative of a Necker cube that had been altered in one region to favor one of the alternative interpretations (the biased region) and measured reports about the perceived organization of the cube over 30-s trials. Regardless of fixation location, responses showed obligatory effects of the bias only when observers attended to the biased region of the cube and not when they attended to the unbiased region of the cube, even when the biased region lay between fixation and the attended unbiased region. On the basis of these experiments, we argue that spatial attention operates through mechanisms of facilitation and inhibition to determine the functional nature of the structural description of an object.