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 efficiency in the processing of targets and the number of intervening distracters. Ln five experiments, observers judged whether the Vertices of two relevant shapes were of the same height. Experiments I and 2 manipulated observers' perceptual set so that identical stimulus displays were perceived as containing either intervening or flanking distracters. The observers mere faster when the distracters were flanking rather than intervening between the targets. Experiments 3-5 varied the number of intervening distracters directly. The observers' response latencies correlated positively with the distracter set-size. Because the distracters were highly discriminable from the targets and the spatial separation between the targets and their interactions with the adjacent distracters were held constant, it was unlikely that the differential reaction times across the conditions were caused by lateral inhibition or response competitions from the distracters. The results suggest the existence of an object-based filtering cost. The implications of the present data for attentional selection over noncontiguous regions are also discussed.