  Two prominent strategies that the human visual system uses to reduce incoming
information are spatial integration and selective attention. Although spatial
integration summarizes and combines information over the visual field,
selective attention can single it out for scrutiny. The way in which these
well-known mechanisms, with rather opposing effects, interact remains largely
unknown. To address this, we had observers perform a gaze-contingent search
task that nudged them to deploy either spatial or feature-based attention to
maximize performance. We found that, depending on the type of attention
employed, visual spatial integration strength changed either in a strong and
localized or a more modest and global manner compared with a baseline
condition. Population code modeling revealed that a single mechanism can
account for both observations: Attention acts beyond the neuronal encoding
stage to tune the spatial integration weights of neural populations. Our study
shows how attention and integration interact to optimize the information flow
through the brain.
