Attention switching in depth using random-dot autostereograms: attention gradient asymmetries.

Random-dot autostereograms (RDASs) were used to investigate attention shifts along the sagittal plane in distractor-free tasks of high perceptual load. In three experiments using a same/different comparison task, the shape of the gradient over five different depths was examined and the conditions under which the gradient is and is not observed were compared. When the target set consisted of five similar objects, a robust asymmetric depth gradient was observed. When the target set consisted of two dissimilar objects, no gradient was observed. The results support a hypothesis of a viewer-centered asymmetric attention gradient in the depth plane that is dependent on perceptual or attentional load defined by target-set discriminability.