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Steven Cholewiak, Romain Vergne, Benjamin Kunsberg, Steven Zucker, Roland Fleming; Distinguishing between texture and shading flows for 3D shape estimation. Journal of Vision 2015;15(12):965. doi: 10.1167/15.12.965.
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© ARVO (1962-2015); The Authors (2016-present)
The visual system can infer 3D shape from orientation flows arising from both texture and shading patterns. However, these two types of flows provide fundamentally different information about surface structure. Texture flows, when derived from distinct elements, mainly signal first-order features (surface slant), whereas shading flow orientations primarily relate to second-order surface properties. It is therefore crucial for the brain to identify whether flow patterns originate from shading or texture to correctly infer shape. One possible approach would be to use 'surface appearance' (e.g. smooth gradients vs. fine-scale texture) to distinguish texture from shading. However, the structure of the flow fields themselves may indicate whether a given flow is more likely due to first- or second-order shape information. Here we test these two possibilities. We generated irregular objects ('blobs') using sinusoidal perturbations of spheres. We then derived two new objects from each blob: One whose shading flow matched the original object's texture flow, and another whose texture flow matched the original's shading flow. Using high and low frequency environment maps to render the surfaces, we were able to manipulate surface appearance independently from the flow structure. This provided a critical test of how appearance interacts with orientation flow when estimating 3D shape and revealed some striking illusions of shape. In an adjustment task, observers matched the perceived shape of a standard object to each comparison object by morphing between the generated shape surfaces. In a 2AFC task, observers were shown two manipulations for each blob and indicated which one matched a briefly flashed standard. Performance was compared to an orientation flow based model and confirmed that observers' judgments agreed with texture and shading flow predictions. Both the structure of the flow and overall appearance are important for shape perception, but appearance cues determine the inferred source of the observed flowfield.
Meeting abstract presented at VSS 2015
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