A Prior for Global Convexity in Local Shape-from-Shading

Langer, Michael; Bülthoff, HH

doi:10.1068/p3178

Cited by 132 publications

(97 citation statements)

References 18 publications

(15 reference statements)

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“…We found that observers' interpretations were systematically biased (difference from 50%, p Ͻ 10 Ϫ5 , bootstrap significance test, 20,000 iterations), with a zero disparity Mach card reported as convex (66%) more frequently than concave (34%). Consistent with previous reports (Langer and Bülthoff, 2001;Liu and Todd, 2004), this suggests that observers have a bias for convex shape interpretations. By adding binocular disparity to the Mach card stimulus, we changed the perceived 3D shape systematically (Fig.…”

Section: Fmri Selective Adaptation For the Ambiguous Mach Card Stimulussupporting

confidence: 81%

Adaptive Estimation of Three-Dimensional Structure in the Human Brain

Preston¹,

Kourtzi²,

Welchman³

2009

J. Neurosci.

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Perceiving the three-dimensional (3D) properties of the environment relies on the brain bringing together ambiguous cues (e.g., binocular disparity, shading, texture) with information gained from short-and long-term experience. Perceptual aftereffects, in which the perception of an ambiguous 3D stimulus is biased away from the shape of a previously viewed stimulus, provide a sensitive means of probing this process, yet little is known about their neural basis. Here, we investigate 3D aftereffects using psychophysical and functional MRI (fMRI) adaptation paradigms to gain insight into the cortical circuits that mediate the perceptual interpretation of ambiguous depth signals. Using two classic bistable stimuli (Mach card, kinetic depth effect), we test aftereffects produced by 3D shapes defined by binocular (disparity) or monocular (texture, shading) depth cues. We show that the processing of ambiguous 3D stimuli in dorsal visual cortical areas (V3B/KO, V7) and posterior parietal regions is modulated by adaptation in line with perceptual aftereffects. Similar behavioral and fMRI adaptation effects for the two types of bistable stimuli suggest common neural substrates for depth aftereffects independent of the inducing depth cues (disparity, texture, shading). In line with current thinking about the role of adaptation in sensory optimization, our findings provide evidence that estimation of 3D shape in dorsal cortical areas takes account of the adaptive context to resolve depth ambiguity and interpret 3D structure.

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Section: Fmri Selective Adaptation For the Ambiguous Mach Card Stimulussupporting

confidence: 81%

Adaptive Estimation of Three-Dimensional Structure in the Human Brain

Preston¹,

Kourtzi²,

Welchman³

2009

J. Neurosci.

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“…It is interesting, for example, that the illusion is stronger for upright than for inverted faces (Hill & Bruce, 1993). Moving away from the special case of faces, Langer and Bülthoff (2001) tried to compare different assumptions about 3-D shape and concluded that the convexity assumption is as strong as two other assumptions: the viewpoint from above and the light from above (but see also van Doorn, Koenderink, & Wagemans, 2011;Wagemans, Van Doorn, & Koenderink, 2010). What is important for this review is that a bias for 3-D convexity over 3-D concavity does not imply an equivalent bias for 2-D convexity over 2-D concavity, because of the difference discussed earlier in how 2-D information is information about 3-D surface curvature-namely, the fact that a concave contour is not the projection of a concave surface.…”

Section: Questionmentioning

confidence: 99%

Processing convexity and concavity along a 2-D contour: figure–ground, structural shape, and attention

Bertamini

Wagemans

2012

Psychon Bull Rev

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Interest in convexity has a long history in vision science. For smooth contours in an image, it is possible to code regions of positive (convex) and negative (concave) curvature, and this provides useful information about solid shape. We review a large body of evidence on the role of this information in perception of shape and in attention. This includes evidence from behavioral, neurophysiological, imaging, and developmental studies. A review is necessary to analyze the evidence on how convexity affects (1) separation between figure and ground, (2) part structure, and (3) attention allocation. Despite some broad agreement on the importance of convexity in these areas, there is a lack of consensus on the interpretation of specific claims-for example, on the contribution of convexity to metric depth and on the automatic directing of attention to convexities or to concavities. The focus is on convexity and concavity along a 2-D contour, not convexity and concavity in 3-D, but the important link between the two is discussed. We conclude that there is good evidence for the role of convexity information in figure-ground organization and in parsing, but other, more specific claims are not (yet) well supported.

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“…S4). By contrast, reversing the two eyes' views had no effect on the perceived depth structure for the unreliable portions of the shapes; instead, observers' judgments were consistent with the 3D shape specified by monocular shape cues in conjunction with a convexity prior (33,34). Thus, consistent with the use of intrinsic disparity markers, in locations where disparity signals are less reliable, observers' judgments of shape rely more on other sources of information about 3D shape.…”

Section: Discussionmentioning

confidence: 54%

Specular reflections and the estimation of shape from binocular disparity

Muryy

Welchman

Blake

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Binocular stereopsis is a powerful visual depth cue. To exploit it, the brain matches features from the two eyes' views and measures their interocular disparity. This works well for matte surfaces because disparities indicate true surface locations. However, specular (glossy) surfaces are problematic because highlights and reflections are displaced from the true surface in depth, leading to information that conflicts with other cues to 3D shape. Here, we address the question of how the visual system identifies the disparity information created by specular reflections. One possibility is that the brain uses monocular cues to identify that a surface is specular and modifies its interpretation of the disparities accordingly. However, by characterizing the behavior of specular disparities we show that the disparity signals themselves provide key information ("intrinsic markers") that enable potentially misleading disparities to be identified and rejected. We presented participants with binocular views of specular objects and asked them to report perceived depths by adjusting probe dots. For simple surfaces-which do not exhibit intrinsic indicators that the disparities are "wrong"-participants incorrectly treat disparities at face value, leading to erroneous judgments. When surfaces are more complex we find the visual system also errs where the signals are reliable, but rejects and interpolates across areas with large vertical disparities and horizontal disparity gradients. This suggests a general mechanism in which the visual system assesses the origin and utility of sensory signals based on intrinsic markers of their reliability.psychophysics | perception | gloss | texture | computational analysis S hiny objects such as sports cars, jewelry, and consumer electronics can be beautiful to look at. However, such objects pose a difficult challenge to the visual system: if all (or most) of the light reaching the eye comes from the reflections of other nearby objects, how does the viewer discern the object itself? This problem becomes more acute when viewing with two eyes. Unlike shading or texture markings, the positions of reflections relative to a specular (shiny) surface depend on the observer's viewpoint. This means that when the surface is viewed binocularly (i.e., from two viewpoints at the same time), corresponding reflections fall on different surface locations. In consequence, the binocular disparities created by specular reflections indicate depth positions displaced from the object's physical surface (1, 2) and the 3D shape specified by disparity can be radically different from the true shape of the object. For special cases, such as an ideal planar mirror, the visual system could not, even in principle, estimate the true depths of the surface from the reflections. However, for more complex shapes, such as a polished metal kettle, we rarely encounter problems judging shape. Most models of biological vision place heavy weight on binocular disparity cues, whereas artificial systems often rely almost exclusively ...

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A Prior for Global Convexity in Local Shape-from-Shading

Cited by 132 publications

References 18 publications

Adaptive Estimation of Three-Dimensional Structure in the Human Brain

Adaptive Estimation of Three-Dimensional Structure in the Human Brain

Processing convexity and concavity along a 2-D contour: figure–ground, structural shape, and attention

Specular reflections and the estimation of shape from binocular disparity

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