Electrophysiological and behavioral "costs" and "benefits" during sustained visual-spatial attention.

Event-related potentials and reaction times were recorded to stimuli flashed to the left and right visual hemifields under different conditions of covert spatial attention. In different blocks, subjects were instructed to allocate attention primarily to either the left or to the right stimulus locations, or to divide attention equivalently between left and right locations (i.e., neutral condition). Regardless of attention condition, however, speeded motor responses were required to stimuli in both visual fields. In comparison to the neutral attention condition, reaction times were slower for targets at unattended locations (costs) and faster for the targets at attended locations (benefits), however, only costs were statistically significant. Significant attention-related enhancements were observed for both early and late ERP components. Cost/benefit analysis of the ERPs revealed ERP benefits in the amplitudes of the early sensory-evoked cortical component P1 (100-160 ms). In contrast, ERP costs appeared only at a relatively late stage of perceptual processing (200-280 ms latency post-stimulus). The relationship between RT and ERP costs and benefits is discussed with respect to models of spatial attention.