Balancing stimulus and goal-driven attentional demands: investigating the role of gamma oscillations in human early visual cortex using magnetoencephalography

"Salient events tend to capture our attention. When such events are irrelevant to something we are looking for they need to be inhibited not to distract us. Efficient allocation of attention involves balancing of attentional demands driven by both salient events and current goals. To deal with the constantly changing visual input in light of attentional goals, it is crucial that visual brain areas participate in this balancing. The aim of this thesis is to investigate the role of early visual areas in the balancing of stimulus and goal-driven attentional demands. I primarily focus on the synchronisation of oscillatory activity in the gamma band, because its role in both neural communication and visual processing makes it a prime candidate for mediating the dynamic balancing of attentional demands. In Chapter 1 I review the literature on behavioural effects and neural processing of attentional demands. In Chapter 2, I focus on how evoked responses in early visual cortex are modulated when stimulus salience and behavioural relevance compete for attentional allocation. I then address how these factors interact to modulate gamma activity in three steps. In Chapter 3, I use a strong gamma-inducing stimulus to investigate how orientation, a stimulus property strongly represented in early visual cortex, affects the gamma response. In Chapter 4, I investigate how directing voluntary attention towards or away from that optimal stimulus affects the gamma response it induces. Finally, I address how stimulus and goal-driven factors combine to influence the gamma response when they compete for attentional allocation in Chapter 5. The main findings in this thesis are that stimulus and goal-driven factors influence gamma synchronisation in early visual cortex at different frequencies, and interact to modulate the gamma response when attentional demands are actively balanced. These findings contribute to our understanding of the role of early visual cortex in both low-level and attentional visual processing. I address the implications of these findings in Chapter 6." -- Abstract.