Differential EEG Markers of Selective Attention and Feature Binding in Visual Search

Previous studies have identified reliable electrophysiological markers of attentional processing within visual search tasks. However, none have identified markers that specifically reflect processes supporting feature binding within objects. This study aims to identify distinct EEG markers that are differentially sensitive to the feature binding and selective attention demands within a visual search paradigm. EEG was recorded while two conjunctive visual search tasks identical in their selective attention demands but differing in the demands placed on cross-cortical interactions were administered to 29 young adults (Mean Age=20.17, 22F). Participants were required to integrate a target’s motion with either its luminance contrast (black or white) or its isoluminant color (red or green) to identify its location (left or right) among 0, 2, or 4 distractor items. Given that luminance and motion information are processed within the same dorsal cortical stream whereas color information is processed within the ventral cortical stream, the motion/color integration task places greater demands on cross-cortical interactions than does the motion/luminance integration task. Thus, these two search tasks differ only in terms of their feature binding demands. Both perceptual (P2, N2) and attentional markers (N2pc, P3b) were compared across conditions in posterior-occipital regions. Response times increased with set size but did not differ across conditions. Similarly, the magnitude of the P2 and N2 (complex pattern and motion-specific markers) and the N2pc (target selection marker) were modulated with set size but did not differ across tasks. In contrast, the contralateral P3b (a marker of top-down attentional enhancement) was unaffected by set size, but modulated across tasks, such that the amplitude was greater in the motion/color condition than in the motion/luminance condition. We believe that this modulation reflects increased reentrant attentional demands needed to maintain feature binding within the target in the across-stream binding condition.