Attentional suppression spreads throughout the visual field

Visual attentional selection enhances the neural response to relevant features and suppresses the response to competing irrelevant features. Feature-based enhancement is known to operate across the visual field, and here we use fMRI in human observers to determine if attentional suppression is restricted to the currently attended spatial location or if attentional suppression also operates in a spatially global manner. On one side of fixation, two moving-dot apertures were presented (e.g. one to the upper right and one to the lower right of fixation) and each aperture contained two orthogonal directions of motion (e.g. leftward and upward motion in one aperture, rightward and downward in the other). Observers monitored the speed of the dots moving in one direction in one of the two apertures (e.g. monitor leftward motion in the upper aperture). We then measured the BOLD response evoked by an additional to-be-ignored unidirectional motion stimulus presented on the other side of a fixation. Consistent with previous reports, the BOLD response was larger when the ignored stimulus matched the currently attended direction compared to when it matched any of the unattended directions. However, the BOLD response was lowest when the ignored stimulus matched the irrelevant direction of motion that was presented in the same aperture as the target compared to one of the other unattended directions. We suggest that the presence of irrelevant features within the focus of spatial attention triggers an attentional suppression mechanism that attenuates the response to the suppressed feature across the entire visual field.