The representation and processing of contour and surface in the human brain

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The visual brain has been interrogated with functional magnetic resonance imaging (fMRI) over the last twenty years, providing significant insight into its organisation. Earlier processing occurs in posterior, 'lower-level' visual brain areas, which contain explicit visual field maps. Such areas are 'mapped' by using visual stimuli that systematically move through the visual field, whilst recording the brain responses. Improvements in techniques have allowed an increasing extent of the visual brain to be mapped in this manner. An alternative method to chart the visual brain's organisation is to test for stimulus selectivity, typically by contrasting the brain's responses to two or more discrete stimulus categories. This approach has identified 'higher-level' category selective areas, for example a shape-selective region referred to as the lateral occipital complex.It was first thought that category selective regions had little or no explicit mapping of the visual field. However, as more visual field maps were discovered some were found to overlap with category selective regions, implying that the two organizations are not mutually exclusive. We will refer to these overlapping regions as 'mid-level' visual field maps. The fact that the two organizing principles intersect gives us an opportunity to understand how the visual brain transitions from low-to-high level processing. Such transitional points should yield valuable insights into the representation of 'abstract' information in higher-level areas.Despite their potential importance, little research on these mid-level regions exists. We aim to address this by focusing on understanding the roles 'mid-level' visual areas play. We have published evidence that mid-level areas can represent abstract information, but the nature of the information represented at this level and the nature of the representations themselves remain unknown. Our overarching aim, therefore, is to find out what visual information is processed and how it represented at this mid-level of the visual system.The mid-level visual areas we will focus on cluster in lateral occipital cortex. At the same time we will also assess visual field maps that lie in dorsal and ventral occipital cortex, to verify that any effects we measure are dissociable. Reassuringly, using this strategy we have already found that certain abstract representations are found in lateral, but not ventral or dorsal mid-level areas. We anticipate therefore that our work will again exhibit dissociable effects in mid-level areas.Our work implies that lateral occipital areas process aspects of contour curvature; we aim to further refine our understanding of these representations. We already have pilot data on some aspects of contour processing and believe therefore that much of the proposed work has a high chance of success. At the same time however we want to explore the processing and representation of 3D surface curvature, to determine whether such properties have shared or unique neural underpinnings. This work is higher risk, but its return could be large as it represents the first opportunity to bring together the study of contour and surface and learn how their relative contributions to our perception of objects is achieved in the human brain.We will combine perceptual measurements and fMRI to reveal how the human brain processes and represents contour and surface curvature. The perceptual experiments will reveal how our stimulus manipulations are perceived; determining which stimuli will be presented during neuroimaging experiments. Both approaches will leverage our expertise in stimulus control, which is grounded in computational methods that can generalize from contour to surface. Further, we have demonstrated that we can characterize our stimuli with perceptual and physical metrics that explain patterns of response in mid-level visual areas and this approach will be extended in the proposed work.