The electrophysiological locus of the redundant target effect on visual discrimination in a dual singleton search task.

Task performance can be enhanced by the addition of extra information to a visual environment in which observers search for a target stimulus. One example of such information is the repetition of the searched-for stimulus; a form of target redundancy. In the present study, the electrophysiological correlates of such target redundancy were investigated in a visual discrimination task. Observers were asked to look for targets in displays that always contained two salient singletons (tilted lines; targets and/or nontargets) against a background of vertical distractor lines. Displays contained either two redundant targets, two nontargets, or a single target and nontarget, at opposite sides of the visual field. Search was most efficient when two targets were shown, and effects of target redundancy were observed on the event-related potential as well. Target redundancy modulated the anterior N2, and the P3 in both an early and a late window. The results are compatible with models of visual attention that support a relatively late (i.e., central or decisional) locus of redundancy processing.