The dynamics of shifting visuospatial attention revealed by event-related potentials

We developed a behavioral task for spatial orienting of attention in which the same physical stimulus cued covert peripheral shifts of attention to either the left or the right visual fields in different conditions. The design enabled us to record the brain activity engaged during spatial shifts of covert attention that was independent from the physical characteristics of the cueing stimulus using event-related potentials (ERPs). ERPs elicited by foveal cues differed according to the predicted target location starting ca. 160 ms, and differences persisted until the occurrence of the target stimuli. Multiple processes were linked to shifting spatial attention during the cue-target interval. The earliest effects consisted of enhanced negative potentials over the posterior scalp contralateral to the cued location. Later effects were concentrated over the right anterior scalp sites, where activity associated with shifts to the right visual field elicited larger positive potentials. The results extend our understanding of the neural system that orients spatial attention by providing valuable information about the temporal dynamics and hemispheric asymmetries of activity within its posterior and anterior regions.