Neural dynamics of surface perception: boundary webs, illuminants, and shape-from-shading
Computer Vision, Graphics, and Image Processing
Adaptive Nonlocal Filtering: A Fast Alternative to Anisotropic Diffusion for Image Enhancement
IEEE Transactions on Pattern Analysis and Machine Intelligence
A neuromorphic model for achromatic and chromatic surface representation of natural images
Neural Networks - 2004 Special issue Vision and brain
A Neural Model of Smooth Pursuit Control and Motion Perception by Cortical Area MST
Journal of Cognitive Neuroscience
Disambiguating Visual Motion by Form-Motion Interaction--a Computational Model
International Journal of Computer Vision
Motion Segmentation and Depth Ordering Using an Occlusion Detector
IEEE Transactions on Pattern Analysis and Machine Intelligence
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Freezing is an effective defense strategy for some prey, because their predators rely on visual motion to distinguish objects from their surroundings. An object moving over a background progressively covers (deletes) and uncovers (accretes) background texture while simultaneously producing discontinuities in the optic flow field. These events unambiguously specify kinetic occlusion and can produce a crisp edge, depth perception, and figure-ground segmentation between identically textured surfaces - percepts which all disappear without motion. Given two abutting regions of uniform random texture with different motion velocities, one region appears to be situated farther away and behind the other (i.e., the ground) if its texture is accreted or deleted at the boundary between the regions, irrespective of region and boundary velocities. Consequently, a region with moving texture appears farther away than a stationary region if the boundary is stationary, but it appears closer (i.e., the figure) if the boundary is moving coherently with the moving texture. A computational model of visual areas V1 and V2 shows how interactions between orientation- and direction-selective cells first create a motion-defined boundary and then signal kinetic occlusion at that boundary. Activation of model occlusion detectors tuned to a particular velocity results in the model assigning the adjacent surface with a matching velocity to the far depth. A weak speed-depth bias brings faster-moving texture regions forward in depth in the absence of occlusion (shearing motion). These processes together reproduce human psychophysical reports of depth ordering for key cases of kinetic occlusion displays.