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 ®elds in di erent 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 di ered according to the predicted target location
starting ca. 160 ms, and di erences persisted until the occurrence of the target stimuli. Multiple processes were linked to shifting
spatial attention during the cue-target interval. The earliest e ects consisted of enhanced negative potentials over the posterior
scalp contralateral to the cued location. Later e ects were concentrated over the right anterior scalp sites, where activity
associated with shifts to the right visual ®eld 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.