What are the neuronal correlates and dynamics of gist processing, and what is its role in the interplay of two modes of visual attention?

The ability for humans to extract information from their environment with no more than brief glimpse is well-establish in vision science. This is known as ‘gist extraction’, and is the product of the first feed-forward sweep of information from the eye, through the visual cortex, and into higher-order cognitive control areas in the frontal lobes. This process results in ‘sparse’ attention, which contains multiple elements including gist. The first aim of this thesis was to more clearly define gist in terms of its neuronal locations and time signatures, including observing the effects of multiple gists destructively colliding (in which the presence of more than one relevant image causes participants to be unable to identify the presence of a cued target). The second aim of the thesis was to explore the relationship between sparse attention and focused attention. As established by the data, sparse attention represents a broad ‘vision at a glance’ understanding of the visual environment. Focused attention represents a narrow mode of attention. The following novel findings were identified in this thesis: 1. Processing of target category gist can be observed neuronally using fMRI techniques in category-selective cortex; these selective areas show different % BOLD signal responses to their preferred targets. Place-selective areas show a greater % BOLD signal change in a perceptually-driven manner, and face- selective regions show a greater BOLD change in a manner requiring both the actual presence and the subjective perception of the target. 2. Destructive interference is a decisional, not a perceptual process; it is associated with the N300 and D220 ERPs, which are indicative of greater resources being allocated to a difficult task, conflict resolution, and decision-making. 3. Sparse and focused attention operate in a serial manner, with the first feed- forward sweep (including gist) producing the conscious percept of the world