Feature-Specific Patterns of Attention and Functional Connectivity in Human Visual Cortex

The ability to successfully allocate attention to a particular feature in the visual world is vital for successful functioning. Attention refers to a narrowing of focus, with increased processing of an attended attribute at the expense of other non-attended dimensions. This attentional mechanism can modulate activity in the visual cortex and beyond. However, the full range of spatial scales at which attentional effects are evident in the visual cortex is still relatively little understood. This thesis aimed to investigate the effects of attentional modulation across the visual cortex at several spatial scales, examining activation at the level of mean activity in individual regions-of-interest, comparing patterns of voxel-level activity, and employing connectivity-style approaches to examine communication between multiple visual areas simultaneously. We identified little robust evidence of differing modulation as a function of attentional task at the univariate level (mean activation within an ROI). However, we note clear differences in patterns of attentional modulation as a function of task when comparing voxel-level patterns of activation in individual visual ROIs at the multivariate level. We also assessed communication between multiple visual regions simultaneously as a function of attentional task. We identify significantly greater positive connectivity during passive viewing than during directed attention tasks. We suggest this finding is representative of a visual ‘default mode’ network, at a smaller spatial scale than traditional connectivity research. Finally, we find the overall pattern of results collected with highly-controlled low-level visual stimuli, generalise relatively well to our experiment investigating attentional effects with an uncontrolled, dynamic and relatively naturalistic stimulus. In this more-naturalistic experiment, we identify little robust evidence of attentional modulation at both the univariate and multivariate levels. We also, however, demonstrate significant differences in patterns of connectivity across ROIs as a function of attentional task.