Functional MRI reveals spatially specific attentional modulation in human primary visual cortex

Selective visual attention can strongly influence perceptual processing, ev en for apparently low-level visual stimuli, Although it is largely accepted that attention modulates neural activity in extrastriate visual cortex, th e extent to which attention operates in the first cortical stage, striate v isual cortex (area V1), remains controversial. Here, functional MRI was use d at high field strength (3 T) to study humans during attentionally demandi ng visual discriminations. Similar, robust attentional modulations were obs erved in both striate and extrastriate cortical areas. Functional mapping o f cortical retinotopy demonstrates that attentional modulations were spatia lly specific, enhancing responses to attended stimuli and suppressing respo nses when attention was directed elsewhere, The spatial pattern of modulati on reveals a complex attentional window that is consistent with object-base d attention but is inconsistent with a simple attentional spotlight. These data suggest that neural processing in V1 is not governed simply by sensory stimulation, but, like extrastriate regions, V1 can be strongly and specif ically influenced by attention.