Attending to quadrants and ring-shaped regions: ERP effects of visual attention in different spatial selection tasks

Attentional modulations of event-related brain potentials (ERPs) were measu red when subjects were cued to attend to a visual quadrant or to a ring-sha ped region of visual space to detect infrequently presented targets within the attended region. Spatial attention directed to quadrants was reflected in modulations of sensory-evoked P1 and N1 components at lateral posterior sites and enhanced negativities (Nds) at midline electrodes that started ar ound 150 ms poststimulus. When attention was directed to ring-shaped region s, no modulations of P1 and N1 amplitudes were found, and Nd effects observ ed at midline electrodes were delayed by about 50 ms. These findings indica te that behavioral effects observed both when attention is directed to cont iguous regions and to general areas of visual space may be caused by differ ent underlying processes. Intraperceptual "sensory gating" mechanisms opera ting in a way suggested by the notion of an attentional "zoom-lens" may be responsible for the selection of single regions, quadrants, or hemifields. When relevant regions are more complex, spatial selectivity will affect pri marily postperceptual processes.