Investigating topographic signatures of global object perception and multifocal attention in human visual cortex

• Main Author: Stoll, Susanne
• Format: Dissertation
• Language: English
• Published: UCL (University College London) 2022

To organize and filter visual information across visual space, the visual system draws upon receptive fields, spatial attention, and perceptual grouping. Receptive fields refer to the portion of visual space altering a neuron's response when visually stimulated. They represent the building blocks of topographic maps in visual cortex, where receptive fields of neighboring neurons correspond to neighboring portions in the retina and visual space. This retinotopy preserves the spatial arrangement of a visual scene. However, receptive fields are not hard-wired spatial filters. Specifically, research on perceptual grouping and spatial attention showed that receptive field properties depend on the observer's perceptual-cognitive state. Spatial attention allows us to prioritize information processing at particular locations in visual space, and evidence suggests receptive fields shift towards attended locations. Perceptual grouping allows us to bind together image elements into global objects and segregate them from the background, and evidence suggests neurons increase their response when their receptive fields contain elements perceived as a figure compared to a background. Across several projects, this thesis investigated this state-dependency at the level of topographic maps in human visual cortex. To this end, an approach to back-project brain measures into visual space was developed, allowing for fine-grained read-outs of topographic signatures. The first project focused on topographic signatures of global object perception and points to a non-generic involvement of higher object-sensitive cortex in perceptual grouping and a suppressionenhancement mechanism, possibly mediating figure-ground perception. The second project investigated topographic signatures of multifocal attention and shows that changes in topographic signatures under uni- or multifocal attention conditions cannot be distinguished from changes for test-retest data. The third project investigated flaws in quantifying topographic signatures and highlights that prior summaries of topographic signatures might be contaminated by regression artifacts. Collectively, these results underscore the potentials and challenges of investigating state-dependent topographic signatures.