The Shading Cue in Context

Wagemans, Johan; Doorn, Andrea J. van; Koenderink, Jan J.

doi:10.1068/i0401

Cited by 31 publications

(29 citation statements)

References 30 publications

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“…Studies that used complex illuminated objects with strong lighting direction cues concluded that lighting cues guide shape-from-shading (6, 7), whereas studies that used weaker lighting cues concluded that they have little effect (8)(9)(10)(11)(12). We discuss the lighting cues in previous studies in further detail in SI Discussion.…”

Section: Resultsmentioning

confidence: 99%

The human visual system's assumption that light comes from above is weak

Morgenstern

Murray

Harris

2011

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

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Every biological or artificial visual system faces the problem that images are highly ambiguous, in the sense that every image depicts an infinite number of possible 3D arrangements of shapes, surface colors, and light sources. When estimating 3D shape from shading, the human visual system partly resolves this ambiguity by relying on the light-from-above prior, an assumption that light comes from overhead. However, light comes from overhead only on average, and most images contain visual information that contradicts the light-from-above prior, such as shadows indicating oblique lighting. How does the human visual system perceive 3D shape when there are contradictions between what it assumes and what it sees? Here we show that the visual system combines the light-from-above prior with visual lighting cues using an efficient statistical strategy that assigns a weight to the prior and to the cues and finds a maximum-likelihood lighting direction estimate that is a compromise between the two. The prior receives surprisingly little weight and can be overridden by lighting cues that are barely perceptible. Thus, the light-from-above prior plays a much more limited role in shape perception than previously thought, and instead human vision relies heavily on lighting cues to recover 3D shape. These findings also support the notion that the visual system efficiently integrates priors with cues to solve the difficult problem of recovering 3D shape from 2D images.

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Section: Resultsmentioning

confidence: 99%

The human visual system's assumption that light comes from above is weak

Morgenstern

Murray

Harris

2011

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

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“…Koenderink, van Doorn, Christou, and Lappin (1996) and found that adding surfacerelated information such as shading, texture, and motion yielded only small improvements in shape judgments beyond those obtained with boundary contours alone. Wagemans, van Doorn, and Koenderink (2010) found that contour shape strongly influenced perception of shape from shading.…”

Section: Boundary Contoursmentioning

confidence: 99%

“…The important point, however, is that the image information is inherently ambiguous. Moreover, experiments have found significant variability between individuals, within individuals, strong effects of the outer contour shape, and both interactions and inconsistencies among spatially separate surface regions (Kleffner & Ramachandran, 1992;van Doorn et al, 2011;Wagemans, van Doorn, & Koenderink, 2010).…”

Section: Image Shadingmentioning

confidence: 99%

Fechner, information, and shape perception

Lappin

Norman

Phillips

2011

Atten Percept Psychophys

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How do retinal images lead to perceived environmental objects? Vision involves a series of spatial and material transformations-from environmental objects to retinal images, to neurophysiological patterns, and finally to perceptual experience and action. A rationale for understanding functional relations among these physically different systems occurred to Gustav Fechner: Differences in sensation correspond to differences in physical stimulation. The concept of information is similar: Relationships in one system may correspond to, and thus represent, those in another. Criteria for identifying and evaluating information include (a)resolution, or the precision of correspondence; (b)uncertainty about which input (output) produced a given output (input); and (c)invariance, or the preservation of correspondence under transformations of input and output. We apply this framework to psychophysical evidence to identify visual information for perceiving surfaces. The elementary spatial structure shared by objects and images is the second-order differential structure of local surface shape. Experiments have shown that human vision is directly sensitive to this higher-order spatial information from interimage disparities (stereopsis and motion parallax), boundary contours, texture, shading, and combined variables. Psychophysical evidence contradicts other common ideas about retinal information for spatial vision and object perception. The fundamental problem of vision is to understand how retinal images lead to perceived environmental objects Spatial vision is so marvelously effective that usually it is taken for granted. We perceive environmental objects but not the visual instrument by which they are revealed. Spatial vision pervades our conscious experience, but our understanding of the underlying visual mechanisms has substantial gaps.Gaps in understanding occur especially at the interfaces between visual subsystems, where information is transferred from one physical and spatial format to another. How does vision transcend vast changes in format-involving 3-D objects and spaces, 2-D optical images, neural spike trains and synaptic interactions in multiple neural areas, conscious perceptions, and behavioral actions? How do immaterial knowledge and experience arise from material objects and events? The present article offers a theoretical framework for addressing these issues-based on the concept of information, involving corresponding relational structures in physically separate domains. We describe criteria for identifying and evaluating structural correspondence and then apply these criteria to research on shape perception. Fechner' s insightIn the 19th century, Gustav Fechner struggled for years to find a scientific rationale for linking the material and mental worlds. Material objects have mass and spatial extent, but mental experience has neither. Some have concluded that mental events belong to a spiritual world. Fechner, however, believed that mind and body are inseparable and that mental events are emerg...

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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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The Shading Cue in Context

Cited by 31 publications

References 30 publications

The human visual system's assumption that light comes from above is weak

The human visual system's assumption that light comes from above is weak

Fechner, information, and shape perception

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

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