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The extraction of 3D shape from texture and shading in the human brain.

Georgieva SS, Todd JT, Peeters R, Orban GA - Cereb. Cortex (2008)

Bottom Line: The results of both passive and active experiments reveal that the extraction of 3D SfT involves the bilateral caudal inferior temporal gyrus (caudal ITG), lateral occipital sulcus (LOS) and several bilateral sites along the intraparietal sulcus.Additional results from psychophysical experiments reveal that this difference in neuronal substrate cannot be explained by a difference in strength between the 2 cues.These results underscore the importance of the posterior part of the lateral occipital complex for the extraction of visual 3D shape information from all depth cues, and they suggest strongly that the importance of shading is diminished relative to other cues for the analysis of 3D shape in parietal regions.

View Article: PubMed Central - PubMed

Affiliation: Laboratorium voor Neuro- en Psychofysiologie, Katholieke Universiteit Leuven School of Medicine, Campus Gasthuisberg, B-3000 Leuven, Belgium.

ABSTRACT
We used functional magnetic resonance imaging to investigate the human cortical areas involved in processing 3-dimensional (3D) shape from texture (SfT) and shading. The stimuli included monocular images of randomly shaped 3D surfaces and a wide variety of 2-dimensional (2D) controls. The results of both passive and active experiments reveal that the extraction of 3D SfT involves the bilateral caudal inferior temporal gyrus (caudal ITG), lateral occipital sulcus (LOS) and several bilateral sites along the intraparietal sulcus. These areas are largely consistent with those involved in the processing of 3D shape from motion and stereo. The experiments also demonstrate, however, that the analysis of 3D shape from shading is primarily restricted to the caudal ITG areas. Additional results from psychophysical experiments reveal that this difference in neuronal substrate cannot be explained by a difference in strength between the 2 cues. These results underscore the importance of the posterior part of the lateral occipital complex for the extraction of visual 3D shape information from all depth cues, and they suggest strongly that the importance of shading is diminished relative to other cues for the analysis of 3D shape in parietal regions.

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(A and C) Activity profiles plotting percent MR signal change compared with fixation condition in the main 3D SfS sensitive regions (L and R caudal ITG) when the same visual stimuli were presented with Lambertian (A) and specular (C) shading surfaces (fixed effect, n = 4). (B and D) Examples of a 3D shape with, respectively, Lambertian (B) and specular (D) shading.
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fig12: (A and C) Activity profiles plotting percent MR signal change compared with fixation condition in the main 3D SfS sensitive regions (L and R caudal ITG) when the same visual stimuli were presented with Lambertian (A) and specular (C) shading surfaces (fixed effect, n = 4). (B and D) Examples of a 3D shape with, respectively, Lambertian (B) and specular (D) shading.

Mentions: In the main experiment, the shading patterns were almost entirely diffuse (i.e., Lambertian) (Fig. S1). A first control experiment, in which 4 of the subjects participated, aimed at comparing the neural substrates for 3D SfS for Lambertian and specular reflectances. Therefore, in the 3D shaded condition, surface reflectance included a 30% specular component (mean luminance 309 cd/m2) (Fig. 12D). The control stimuli for this experiment were built following the same procedure described in the main shading experiment, but matched to 3D shaded condition with specular surfaces. In these 4 subjects, 8 time series were tested in a single scan session, in order to be compared with the 8 series obtained in the main experiment. Subjects were required only to fixate the fixation target. Subjects made on average 4 or 5 saccades per block in the specular and Lambertian shading runs, respectively. The number of saccades was not significantly different amongst conditions (both 1-way ANOVAs P > 0.8).


The extraction of 3D shape from texture and shading in the human brain.

Georgieva SS, Todd JT, Peeters R, Orban GA - Cereb. Cortex (2008)

(A and C) Activity profiles plotting percent MR signal change compared with fixation condition in the main 3D SfS sensitive regions (L and R caudal ITG) when the same visual stimuli were presented with Lambertian (A) and specular (C) shading surfaces (fixed effect, n = 4). (B and D) Examples of a 3D shape with, respectively, Lambertian (B) and specular (D) shading.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2536698&req=5

fig12: (A and C) Activity profiles plotting percent MR signal change compared with fixation condition in the main 3D SfS sensitive regions (L and R caudal ITG) when the same visual stimuli were presented with Lambertian (A) and specular (C) shading surfaces (fixed effect, n = 4). (B and D) Examples of a 3D shape with, respectively, Lambertian (B) and specular (D) shading.
Mentions: In the main experiment, the shading patterns were almost entirely diffuse (i.e., Lambertian) (Fig. S1). A first control experiment, in which 4 of the subjects participated, aimed at comparing the neural substrates for 3D SfS for Lambertian and specular reflectances. Therefore, in the 3D shaded condition, surface reflectance included a 30% specular component (mean luminance 309 cd/m2) (Fig. 12D). The control stimuli for this experiment were built following the same procedure described in the main shading experiment, but matched to 3D shaded condition with specular surfaces. In these 4 subjects, 8 time series were tested in a single scan session, in order to be compared with the 8 series obtained in the main experiment. Subjects were required only to fixate the fixation target. Subjects made on average 4 or 5 saccades per block in the specular and Lambertian shading runs, respectively. The number of saccades was not significantly different amongst conditions (both 1-way ANOVAs P > 0.8).

Bottom Line: The results of both passive and active experiments reveal that the extraction of 3D SfT involves the bilateral caudal inferior temporal gyrus (caudal ITG), lateral occipital sulcus (LOS) and several bilateral sites along the intraparietal sulcus.Additional results from psychophysical experiments reveal that this difference in neuronal substrate cannot be explained by a difference in strength between the 2 cues.These results underscore the importance of the posterior part of the lateral occipital complex for the extraction of visual 3D shape information from all depth cues, and they suggest strongly that the importance of shading is diminished relative to other cues for the analysis of 3D shape in parietal regions.

View Article: PubMed Central - PubMed

Affiliation: Laboratorium voor Neuro- en Psychofysiologie, Katholieke Universiteit Leuven School of Medicine, Campus Gasthuisberg, B-3000 Leuven, Belgium.

ABSTRACT
We used functional magnetic resonance imaging to investigate the human cortical areas involved in processing 3-dimensional (3D) shape from texture (SfT) and shading. The stimuli included monocular images of randomly shaped 3D surfaces and a wide variety of 2-dimensional (2D) controls. The results of both passive and active experiments reveal that the extraction of 3D SfT involves the bilateral caudal inferior temporal gyrus (caudal ITG), lateral occipital sulcus (LOS) and several bilateral sites along the intraparietal sulcus. These areas are largely consistent with those involved in the processing of 3D shape from motion and stereo. The experiments also demonstrate, however, that the analysis of 3D shape from shading is primarily restricted to the caudal ITG areas. Additional results from psychophysical experiments reveal that this difference in neuronal substrate cannot be explained by a difference in strength between the 2 cues. These results underscore the importance of the posterior part of the lateral occipital complex for the extraction of visual 3D shape information from all depth cues, and they suggest strongly that the importance of shading is diminished relative to other cues for the analysis of 3D shape in parietal regions.

Show MeSH