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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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Luminance histograms and amplitude spectra of the stimuli used in the main experiment. (A) Luminance histograms averaged over all 11 shapes (the error bars indicate standard deviations [SDs]) of 3D shaded, center-shaded, and shaded-blob stimuli. Yellow bars indicate the luminance of the uniform-luminance stimuli and the arrows indicate the light and dark gray values for each of the unshaded-blob shapes (see Materials and Methods). (B) Amplitude spectra averaged over the 11 shapes (the error bars indicate SDs). Upper panel: spectra of 3D shaded (black line), center-shaded (orange line), shaded-blob (dark red), and unshaded-blob (light red) shapes; lower panel: spectra of 3D shaded (black line), uniform luminance (yellow line), and pixel scrambled (olive line). The stars indicate frequencies at which spectra differed significantly (1-way ANOVA, P < 0.05) between 3D shaded stimuli and the 2D controls (orange: center shaded; olive: pixel scrambled). Notice that the amplitude spectra were not calculated on the interior of the shapes but on the central 15.4° x 14.5° part of the display.
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fig2: Luminance histograms and amplitude spectra of the stimuli used in the main experiment. (A) Luminance histograms averaged over all 11 shapes (the error bars indicate standard deviations [SDs]) of 3D shaded, center-shaded, and shaded-blob stimuli. Yellow bars indicate the luminance of the uniform-luminance stimuli and the arrows indicate the light and dark gray values for each of the unshaded-blob shapes (see Materials and Methods). (B) Amplitude spectra averaged over the 11 shapes (the error bars indicate SDs). Upper panel: spectra of 3D shaded (black line), center-shaded (orange line), shaded-blob (dark red), and unshaded-blob (light red) shapes; lower panel: spectra of 3D shaded (black line), uniform luminance (yellow line), and pixel scrambled (olive line). The stars indicate frequencies at which spectra differed significantly (1-way ANOVA, P < 0.05) between 3D shaded stimuli and the 2D controls (orange: center shaded; olive: pixel scrambled). Notice that the amplitude spectra were not calculated on the interior of the shapes but on the central 15.4° x 14.5° part of the display.

Mentions: In the SfS experiment (Fig. 1B and Fig. S1), the surfaces in the 3D shaded condition (Fig. S1) were illuminated by a rectangular area light at a 22° angle directly above the line of sight, and they were rendered using a standard Blinn reflectance model, in which the shading at each point is determined as a linear combination of its ambient, diffuse and specular components (mean luminance 367 cd/m2). In the main experiment the reflectance was Lambertian, with no specular component. A number of control conditions were included in which the patterns of shading did not produce a compelling perception of a 3D surface, yet they had luminance histograms and/or Fourier amplitude spectra that were closely matched to those of the 3D displays (Fig. 2). The first method we employed for eliminating the appearance of depth in the (2D) pixel-scrambled condition was to randomly reposition the pixels (2.3 × 2.3 minarc) within the boundary of each object. The luminance histograms in these displays were identical to those in the 3D shaded condition, but the local luminance gradients were quite different. Note in Figure 2 that the 3D shaded stimuli contained relatively large regions of nearly uniform luminance. The 2D uniform-luminance condition was designed to create flat looking stimuli that shared this aspect of the 3D displays. The stimuli in that condition included 11 silhouettes of different uniform luminance covering the same luminance range as in the 3D shaded condition (Fig. 2A, vertical straight yellow bars). Two additional control conditions were created that attempted to mimic the pattern of shading gradients in the 3D displays without eliciting the appearance of a 3D surface. In the center-shaded condition, all stimuli had a luminance pattern that increased radially from the center of each silhouette. In the (2D) shaded-blob condition each silhouette contained 3–5 randomly shaped ovals with blurred edges on a light background. A 1-way analysis of variance (ANOVA) revealed that the luminance histograms in these latter 2 conditions did not differ significantly from that of the 3D condition. Finally, a 2D unshaded-blob condition was included that was identical to the shaded blobs, except that all of the smooth luminance gradients were eliminated. This was achieved by thresholding the image intensities to contain just 2 possible luminance values. In all shading conditions, the 11 different stimuli were presented ranging in size from 5° to 15° (Fig. S1).


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

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

Luminance histograms and amplitude spectra of the stimuli used in the main experiment. (A) Luminance histograms averaged over all 11 shapes (the error bars indicate standard deviations [SDs]) of 3D shaded, center-shaded, and shaded-blob stimuli. Yellow bars indicate the luminance of the uniform-luminance stimuli and the arrows indicate the light and dark gray values for each of the unshaded-blob shapes (see Materials and Methods). (B) Amplitude spectra averaged over the 11 shapes (the error bars indicate SDs). Upper panel: spectra of 3D shaded (black line), center-shaded (orange line), shaded-blob (dark red), and unshaded-blob (light red) shapes; lower panel: spectra of 3D shaded (black line), uniform luminance (yellow line), and pixel scrambled (olive line). The stars indicate frequencies at which spectra differed significantly (1-way ANOVA, P < 0.05) between 3D shaded stimuli and the 2D controls (orange: center shaded; olive: pixel scrambled). Notice that the amplitude spectra were not calculated on the interior of the shapes but on the central 15.4° x 14.5° part of the display.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig2: Luminance histograms and amplitude spectra of the stimuli used in the main experiment. (A) Luminance histograms averaged over all 11 shapes (the error bars indicate standard deviations [SDs]) of 3D shaded, center-shaded, and shaded-blob stimuli. Yellow bars indicate the luminance of the uniform-luminance stimuli and the arrows indicate the light and dark gray values for each of the unshaded-blob shapes (see Materials and Methods). (B) Amplitude spectra averaged over the 11 shapes (the error bars indicate SDs). Upper panel: spectra of 3D shaded (black line), center-shaded (orange line), shaded-blob (dark red), and unshaded-blob (light red) shapes; lower panel: spectra of 3D shaded (black line), uniform luminance (yellow line), and pixel scrambled (olive line). The stars indicate frequencies at which spectra differed significantly (1-way ANOVA, P < 0.05) between 3D shaded stimuli and the 2D controls (orange: center shaded; olive: pixel scrambled). Notice that the amplitude spectra were not calculated on the interior of the shapes but on the central 15.4° x 14.5° part of the display.
Mentions: In the SfS experiment (Fig. 1B and Fig. S1), the surfaces in the 3D shaded condition (Fig. S1) were illuminated by a rectangular area light at a 22° angle directly above the line of sight, and they were rendered using a standard Blinn reflectance model, in which the shading at each point is determined as a linear combination of its ambient, diffuse and specular components (mean luminance 367 cd/m2). In the main experiment the reflectance was Lambertian, with no specular component. A number of control conditions were included in which the patterns of shading did not produce a compelling perception of a 3D surface, yet they had luminance histograms and/or Fourier amplitude spectra that were closely matched to those of the 3D displays (Fig. 2). The first method we employed for eliminating the appearance of depth in the (2D) pixel-scrambled condition was to randomly reposition the pixels (2.3 × 2.3 minarc) within the boundary of each object. The luminance histograms in these displays were identical to those in the 3D shaded condition, but the local luminance gradients were quite different. Note in Figure 2 that the 3D shaded stimuli contained relatively large regions of nearly uniform luminance. The 2D uniform-luminance condition was designed to create flat looking stimuli that shared this aspect of the 3D displays. The stimuli in that condition included 11 silhouettes of different uniform luminance covering the same luminance range as in the 3D shaded condition (Fig. 2A, vertical straight yellow bars). Two additional control conditions were created that attempted to mimic the pattern of shading gradients in the 3D displays without eliciting the appearance of a 3D surface. In the center-shaded condition, all stimuli had a luminance pattern that increased radially from the center of each silhouette. In the (2D) shaded-blob condition each silhouette contained 3–5 randomly shaped ovals with blurred edges on a light background. A 1-way analysis of variance (ANOVA) revealed that the luminance histograms in these latter 2 conditions did not differ significantly from that of the 3D condition. Finally, a 2D unshaded-blob condition was included that was identical to the shaded blobs, except that all of the smooth luminance gradients were eliminated. This was achieved by thresholding the image intensities to contain just 2 possible luminance values. In all shading conditions, the 11 different stimuli were presented ranging in size from 5° to 15° (Fig. S1).

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
Related in: MedlinePlus