The perceptual consequences of the attentional bias: evidence for distractor removal.

A fundamental question of attentional research concerns the perceptual consequences of attention. Spatial attention can enhance stimuli within the focus of attention relative to stimuli outside; or attention can remove the influence of distracting stimuli and other forms of external noise inside the focus of attention. It is known that both strategies apply depending on how attention is cued to a location in space. Here we asked which strategy applies in an uncued situation in which people show a spontaneous bias of attention to the left side. To measure bias, we used a gratingscales task with stimuli corrupted by pixel noise. If biased attention resulted in biased stimulus enhancement its effect should be largest when there is little noise or few distractors within the attended region, and bias should decline with increasing noise. If, however, bias caused distractors to be removed asymmetrically, larger bias should show up with noisy stimuli. We found that bias rose exponentially as noise increased, in agreement with the external noise removal model, and we found evidence that noise modified interhemispheric competition between attentional systems. Our data offer new insights into the neural mechanisms of the right-hemisphere dominance in spatial and attentional tasks.