Central perceptual load does not reduce ipsilesional flanker interference in parietal extinction

In healthy individuals, filtering of distractors improves when the perceptual difficulty, or load, of a central task increases. Following an earlier study by Lavie and Robertson (2001), this study examined whether increasing the perceptual load of a visual discrimination task attenuates the influence of ipsilesional and contralesional distractors in patients with spatial extinction. The authors used a flanker task in which participants identified a central target letter flanked by congruent, incongruent, or neutral distractors in the left and right hemifields. Perceptual load was manipulated by positioning the central target letter above or below a hash mark (#) in the low-load condition, or a letter ("R") in the high-load condition. Target identification was significantly more difficult under high load than low load. Despite this difference in task difficulty, the interference from incongruent flankers was equivalent across the two load conditions, for both contralesional and ipsilesional flankers. Our results suggest that perceptual load does not attenuate the distracting influence of ipsilesional stimuli. Rather, selectivity is strongly influenced by the strength of representations in brain areas that code salience across the visual field.