An object-based cost of visual filtering
Although evidence for object-based attention has been reported in a variety of paradigms, few studies have examined directly the relationship between the processing efficiency of the targets and the number of intervening distractors. In five experiments, observers judged whether the vertices of two relevant shapes were of the same height. Experiments 1 and 2 manipulated observers' perceptual set so that identical stimulus displays were perceived as containing either intervening or flanking distractors. Observers were faster when the distractors were flanking rather than intervening the targets. Experiments 3 to 5 varied the number of intervening distractors directly. Observers' response latencies correlated positively with the distractor set-size. Because distractors were highly discriminable from targets, the spatial separation between the targets and their interactions with the adjacent distractors were held constant, the differential reaction times across the conditions were unlikely to be caused by lateral inhibition or response competitions from the distractors. The results suggest the existence of an object-based filtering cost. Implications of the present data on attentional selection over noncontiguous regions are also discussed.