Electrophysiological correlates of attention-spreading in visual grouping.

This study examined event-related potentials in a sustained-attention task that involved bilateral stimulus arrays, which were connected or unconnected by a line. Spatial attention was reflected by a large amplitude of posterior event-related potentials at the hemisphere contralateral, rather than ipsilateral, to the attended hemi-field. The earliest attention effect (P1, 100-160 ms poststimulus) was not affected by connectedness. The subsequent attention effect (N2pc, 190-300 ms) was observed when the target feature appeared in the attended hemi-field, whereas this effect was not seen in the early phase (190-250 ms) in the connected condition. The results indicate that the lateralized event-related potential reflects transient attention-spreading in association with perceptual grouping.