Symmetry as a cue to object and scene representations in human visual cortex

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The human visual system must convert the 2D image arriving at the retina into a 3D representation of the visual scene that we can use to perceive and interact with the world. Visual symmetry is an important cue to this process and has been found to elicit strong responses in visually responsive brain areas. Most studies of symmetry in the context of visual perception have used a limited range of stimulus parameters: (1) Reflection rather than other types of symmetry, (2) symmetry axes at a single image location, and (3) symmetries in the fronto-parallel image plane. The proposed research program builds on recent advances in order to address these limitations and enhance our understanding of symmetry as a cue to object and scene perception. Project 1 will explore how sensitivity to symmetry is modulated by symmetry type, tiling and skew. My prior work shows that visual brain areas are sensitive to symmetries other than reflection, and that textures in which symmetries are tiled across the plane produce robust visual responses, but it is unclear how tiling and symmetry type modulate activity across brain areas. The skew manipulation is motivated by the fact that although symmetries commonly occur in the natural world, symmetrical image-plane projections onto the retina rarely occur under natural viewing. It is thus natural to ask to what extent the visual system can overcome distortions introduced when symmetries in the world produce "skewed" projections onto the retina. To address the hypothesis that these manipulations differentially drive distinct symmetry-sensitive sub-networks in human visual cortex, I will use brain imaging methods to measure the amplitude, timing and cortical sources of responses to symmetry with high temporal and spatial precision. This project will provide a more complete characterization of symmetry tuning in the visual system and has the potential to connect distinct branches of the literature. Project 2 will address the hypothesis that sensitivity to symmetry is the result of learning as infants and young children are exposed to symmetries in their visual environment, and that responses to symmetry in human visual cortex should therefore change over early development. I will test this by comparing symmetry responses in infants and adults. To our knowledge, this will be the first brain imaging study to investigate symmetry perception in infants or young children. This study will reveal any sensitivity to symmetry that may exist in early visual development, and provide cues as to how encoding of symmetry changes with exposure to the natural world. This research program addresses an important gap between the symmetry and 3D object and scene perception literatures using well-controlled stimuli combined with state-of-the-art brain imaging techniques. The findings have the potential to deepen our understanding of the role of symmetry in natural vision, and inform related research in visual neuroscience and computer vision.