Attentional load modulates subconscious orientation processing

Abstract

In load theory of attention (Lavie, 1995, 2005), competition between task-relevant and task-irrelevant stimuli for limited-capacity attention does not depend on conscious perception of the irrelevant stimuli. Here we examine whether the level of perceptual load in a relevant task would determine unconscious processing of invisible stimuli. Subjects performed an RSVP task at fixation under conditions of low perceptual load (detecting color targets) or high perceptual load (detecting conjunctions of color and shape). A task-irrelevant tilted grating was also presented monocularly in the periphery, and was suppressed from awareness by continuously flashing a mask stimulus at the same peripheral location in the other eye. Increasing the perceptual load of the fixation task reduced orientation-specific adaptation to the irrelevant and effectively invisible tilted grating. We conclude that even unconcious perception of orientation depends on the availability of spare attentional capacity from a foveal task. These results extend load theory to account for unconscious perception and rule out claims that attentional effects are restricted to conscious representations(Lamme, 2003; Block, 1996).