Amelia Harrison

Presentation Title

Distributing attention does not degrade stimulus representations in visual cortex

Abstract

When spatial attention is distributed across multiple visual field locations, performance in visual tasks is often impaired. This bottleneck is evident in behavioral and neural studies, especially when using complex stimuli, and is echoed in behavioral and neural measurements of visual working memory. Some studies have suggested that this is because distributing attention results in lower attentional enhancement in visual cortex compared to focused attention, while others support a bottleneck at a post-perceptual
decision-making stage. To characterize how stimulus representations in neural priority maps reflect these constraints and discriminate between these models, we scanned participants with functional magnetic resonance imaging (fMRI) while they performed a selective attention task in which they were cued on each trial to discriminate a target that appeared at the fixation point, 1 cued location, or 2 cued locations. Using a spatial inverted encoding model, we reconstructed representations of the stimuli within retinotopic brain
regions. We examined the strength of these representations when both stimuli were attended, and found that strikingly, both stimulus representations were enhanced when attended, with an equivalent increase in strength as observed with focused attention directed to a single stimulus. This pattern was consistent across retinotopic cortex, with no evidence for graded attentional enhancement in any region. Thus, our results are consistent with a model whereby fMRI signals are enhanced when a stimulus is attended, and the degree of enhancement does not wane as the number of attended stimuli increases. Such a ‘relevance’ marker may be used to identify neural populations for selective readout from relevant locations during decision-making.