Neural correlates of shape from shading

Mamassian, Pascal; Jentzsch, Ines; Bacon, Benoît A.; Schweinberger, Stefan R.

doi:10.1097/00001756-200305230-00013

Cited by 24 publications

(20 citation statements)

References 13 publications

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“…In contrast, the activity in higher visual areas (in particular in parietal areas) was not affected by lighting direction (left vs. right), but instead reflected the perceived shape (convex vs. concave). Past studies had already highlighted several regions of the shape-from-shading network, in particular early visual areas (5)(6)(7)(8)(9) and to a lesser extent higher extrastriate (10) and parietal areas (11). Our study helps delineating the functions mediated by these different cortical areas.…”

Section: Discussionmentioning

confidence: 51%

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Prior knowledge of illumination for 3D perception in the human brain

Gerardin

Kourtzi

Mamassian

2010

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

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In perceiving 3D shape from ambiguous shading patterns, humans use the prior knowledge that the light is located above their head and slightly to the left. Although this observation has fascinated scientists and artists for a long time, the neural basis of this "light from above left" preference for the interpretation of 3D shape remains largely unexplored. Combining behavioral and functional MRI measurements coupled with multivoxel pattern analysis, we show that activations in early visual areas predict best the light source direction irrespective of the perceived shape, but activations in higher occipitotemporal and parietal areas predict better the perceived 3D shape irrespective of the light direction. These findings demonstrate that illumination is processed earlier than the representation of 3D shape in the visual system. In contrast to previous suggestions, we propose that prior knowledge about illumination is processed in a bottom-up manner and influences the interpretation of 3D structure at higher stages of processing.functional MRI | multi-voxel pattern analysis | shape-from-shading | visual cortex | bottom-up processing A lthough the perception of 3D shape is critically important for actions and interactions in the environments we inhabit, most depth cues are ambiguous. As a result, the brain requires additional information based on previous experience with the environment to infer 3D shape from depth cues. In particular, the inference of 3D shape from shading patterns (i.e., using image luminance intensity variations to derive the shape of a surface) relies on the assumption that the scene illuminant is above our heads and slightly to the left (1, 2). Understanding the illumination of a visual scene has fascinated artists and scientists for a long time (3, 4), but the neural basis of this "light from above left" preference for the interpretation of 3D shape remains largely unexplored. Although the light-from-above preference is consistent with an ecological explanation, the left bias remains entirely unexplained. More generally, the light-from-above preference provides a simple example of the way the brain represents prior knowledge and opens the door for the investigation of other types of prior knowledge related to our perception of the motion, shape, and color of objects.Previous neurophysiological and imaging studies have implicated several brain regions in the processing of shape-fromshading: primary visual cortex (V1) (5-9), areas in the caudal inferior temporal gyrus (10) and the inferior parietal sulcus (11). However, the functions mediated by these different cortical areas may differ. In particular, interpreting shape-from-shading may involve at least two different stages of processing. At the first stage, the contrast polarity of edges in the image (dark or bright) is analyzed and related to the light direction so that left and right light directions can be discriminated. At the second stage, contrast edges are grouped together to form 3D shapes so that convex and concave shapes can be dis...

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Section: Discussionmentioning

confidence: 51%

“…Previous neurophysiological and imaging studies have implicated several brain regions in the processing of shape-fromshading: primary visual cortex (V1) (5)(6)(7)(8)(9), areas in the caudal inferior temporal gyrus (10) and the inferior parietal sulcus (11). However, the functions mediated by these different cortical areas may differ.…”

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confidence: 99%

Prior knowledge of illumination for 3D perception in the human brain

Gerardin

Kourtzi

Mamassian

2010

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

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“…The right hemisphere is better for a whole variety of tasks. For example, Mamassian, Jentzsch, Bacon, and Schweinberger (2003) recently showed that a shape-from-shading task activates the right hemisphere of the brain more than the left. So what is special about the right hemisphere?…”

Section: Discussionmentioning

confidence: 99%

Spatio‐temporal dynamics of face recognition in a flash: it's in the eyes

2004

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We adapted the Bubbles procedure [Vis. Res. 41 (2001) 2261] to examine the effective use of information during the first 282 ms of face identification. Ten participants each viewed a total of 5100 faces sub-sampled in space-time. We obtained a clear pattern of effective use of information: the eye on the left side of the image became diagnostic between 47 and 94 ms after the onset of the stimulus; after 94 ms, both eyes were used effectively. This preference for the eyes increased with practice, and was not solely due to the informativeness of the eyes for the task at hand. The bias for the eye on the left side of the image is explained in terms of hemispheric specialization. Although there were individual differences, most participants exhibited this pattern of effective use of information. An intriguing finding is that most participants displayed a clear sinusoïdal modulation of effective use of attention through time with a frequency of about 10.6 Hz.

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“…There are only two ERP studies that have reported relevant data. Mamassian, Jentzsch, Bacon, and Schweinberger (2003) presented ambiguously shaded patterns and examined VEPs. They found correlations bechange in voltage in the P1 latency range reflects an orientation effect over the occipital cortex in the latency range between 80 and 200 msec.…”

Section: Discussionmentioning

confidence: 99%