Attentional inhibition of visual processing in human striate and extrastriate cortex.

Allocating attention to a spatial location in the visual field is associated with an increase in the cortical response evoked by a stimulus at that location, compared to when the same stimulus is unattended. We used event-related functional magnetic resonance imaging to investigate attentional modulation of the cortical response to a stimulus probe at an attended location and to multiple probes at unattended locations. A localizer task and retinotopic mapping were used to precisely identify the cortical representations of each probe within striate (V1) and extrastriate cortex (V2, VP, V3, V4v, and V3A). The magnitude and polarity of attentional modulation were assessed through analysis of event-related activity time-locked to shifts in spatial attention. Attentional facilitation at the attended location was observed in striate and extrastriate cortex, corroborating earlier findings. Attentional inhibition of visual stimuli near the attended location was observed in striate cortex, and attentional inhibition of more distant stimuli occurred in both striate and extrastriate cortex. These findings indicate that visual attention operates both through facilitation of visual processing at the attended location and through inhibition of unattended stimulus representations in striate and extrastriate cortex.