Watching where you look: modulation of visual processing of foveal stimuli by spatial attention.

Two experiments investigated the effect of sustained selective spatial attention upon the perceptual analysis of stimuli within the center of gaze. Spatial attention has typically been studied in relation to peripheral stimuli, and its relevance to the processing of central stimuli has remained relatively ignored. Here, behavioral measures in normal human volunteer participants showed that focused spatial attention can also influence responses to central stimuli, over and beyond the advantage conferred by their foveation. Event-related potentials (ERPs) showed that the action of attention upon foveal stimuli included the modulation of perceptual processing in extrastriate visual areas. Surprisingly, the visual modulation revealed an intriguing and consistent pattern of hemispheric asymmetry, in both experiments. These findings show that in addition to the established right hemisphere dominance of the brain areas that direct attention, the consequences of directed attention may also be asymmetrical.