Kanizsa subjective figures can act as occluding surfaces at parallel stages of visual search

Four experiments examined whether Kanizsa subjective figures can induce amodal completion of a notched circle at parallel stages of visual search. Search for the notched circle among full circles was slow and inefficient when the notched circle appeared stereoscopically behind an abutting subjective surface, as if occluded by it. However, search became efficient and parallel when the notched and completed circles appeared nearer so that the subjective figures could not act as occluders. Control studies ruled out explanations in terms of low spatial frequencies, grouping of aligned edges, or the depth of the circles per se. Multiple Kanizsa subjective figures can be coded in parallel as occluding surfaces; such coding is obligatory because it arises even when highly detrimental to performance.