Attentional modulations in the visual cortex in the absence of visual stimulation

Every day we perceive visual scenes filled with different stimuli. Visual attention allows us to select the information that is most relevant to ongoing behaviour. The aim of this thesis is to explore how top-down modulations of activity in the human visual cortex affect perception and how attention interacts with visual processing in the brain. Specifically, we investigate the role of the modulation that occurs after a cue to attend but before onset of a visual stimulus, referred to in the literature as pre-stimulus attentional modulation, using fMRI methods alongside behavioural measurements. The main focus of the first three experiments is on the interactions between pre-stimulus attentional modulation and modulation by attention of the stimulus-evoked response. Results overall suggest that pre-stimulus activity is correlated with the effects of attention on the stimulus-evoked response and that the two attentional effects may therefore reflect a single process. The aim of the fourth experiment is to study the interaction of spatial and feature-based attention, and the results suggest that when both are engaged together, visual cortical areas do not benefit in an additive way, suggesting either that one dominates or that attentional resources saturate. The fifth experiment investigates the interaction of pre-stimulus activity with the speed and accuracy of saccade movements, and the results suggest no relation between those two processes. Finally the last two experiments focus on the role of pre-stimulus attentional modulation in perceptual learning, and the results strongly suggest that attentional modulation is involved in this process. Based on the results of these experiments, the role of pre- stimulus attentional modulation in visual processing is discussed