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Effects of spatial and feature attention on disparity-rendered structure-from-motion stimuli in the human visual cortex.

Ip IB, Bridge H, Parker AJ - PLoS ONE (2014)

Bottom Line: Here we test whether this non-spatial component can co-select individual features that are perceptually bound into a coherent object.Our study used binocular disparity and visual motion to define disparity structure-from-motion (dSFM) stimuli.Our results demonstrate that feature and global feature attention effects are variable across participants, suggesting that the feature attention system may be limited in its ability to automatically select features within the attended object.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Anatomy & Genetics, University of Oxford, Oxford, United Kingdom; Nuffield Department of Clinical Neurosciences, The Oxford Centre for Functional Magnetic Resonance Imaging of the Brain, University of Oxford, Oxford, United Kingdom.

ABSTRACT
An important advance in the study of visual attention has been the identification of a non-spatial component of attention that enhances the response to similar features or objects across the visual field. Here we test whether this non-spatial component can co-select individual features that are perceptually bound into a coherent object. We combined human psychophysics and functional magnetic resonance imaging (fMRI) to demonstrate the ability to co-select individual features from perceptually coherent objects. Our study used binocular disparity and visual motion to define disparity structure-from-motion (dSFM) stimuli. Although the spatial attention system induced strong modulations of the fMRI response in visual regions, the non-spatial system's ability to co-select features of the dSFM stimulus was less pronounced and variable across subjects. Our results demonstrate that feature and global feature attention effects are variable across participants, suggesting that the feature attention system may be limited in its ability to automatically select features within the attended object. Careful comparison of the task design suggests that even minor differences in the perceptual task may be critical in revealing the presence of global feature attention.

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Stimuli and experimental paradigm.A: Structure-from-motion cylinders disambiguated by binocular disparity are perceived as rotating counter-clockwise (bottom left) or clockwise (bottom right) as controlled by the disparity of the right and left-wards moving surfaces (adapted from Dodd et al., 2001). B: Schematic diagram of the behavioral task used in the MRI-scanner, illustrating an example trial where attention is cued to the right side. For cued cylinders, participants reported whether the speed of rotation in the 1st and 2nd interval was different, while uncued cylinders were ignored.
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pone-0100074-g001: Stimuli and experimental paradigm.A: Structure-from-motion cylinders disambiguated by binocular disparity are perceived as rotating counter-clockwise (bottom left) or clockwise (bottom right) as controlled by the disparity of the right and left-wards moving surfaces (adapted from Dodd et al., 2001). B: Schematic diagram of the behavioral task used in the MRI-scanner, illustrating an example trial where attention is cued to the right side. For cued cylinders, participants reported whether the speed of rotation in the 1st and 2nd interval was different, while uncued cylinders were ignored.

Mentions: Stimuli were structure-from-motion cylinders, each composed of a 5°×5° field of 125 white (57.5 cd/m2) and black (1.9 cd/m2) dots (0.2° size, anti-aliased for sub-pixel resolution) moving at a sinusoidal velocity and disparity profile in opposite directions around a vertical axis on a gray background (17.8 cd/m2). Cylinders were centered ±5.5° either side of the vertical midline and 4.5° below the horizontal fixation plane. The peak velocity and binocular disparity was at the midline of the cylinder and decreased towards the edges. A center-to-front disparity of 0.09° describes the absolute difference in degrees of visual angle between the nearest or farthest point of the cylinder to the fixation plane amounting to 0.09° positive and 0.09° negative disparity. A positive disparity corresponds to the rightwards surface moving in front of the fixation point and the leftwards surface behind. When viewed from the top, this generates the perception of counter-clockwise rotation. The reversed parameters generate clockwise rotation. Average angular rotation speed of cylinders ranged between 100°/s–177°/s, i.e. a dot would require between 2–3.6 s to complete a 360° rotation around the central axis. When a dot reached the edge of the cylinder, it was redrawn with the matching disparity and velocity gradient for dots moving in the opposite direction. Dots were plotted in randomly distributed positions: vertical positions were chosen homogenously along the height of the cylinder, and each dot position was slightly perturbed to prevent the appearance of a regular pattern of dots; horizontal positions were chosen to be homogenously distributed along 0–360° around the axis of the cylinder. The lifetime of individual dots was kept short to facilitate SFM-perception through motion and depth cues [10], [18], [19], [20]. On each video frame, 2% of the dots disappeared and were re-plotted in a random location on each video frame with a velocity appropriate to the new location. The dots of the cylinders were in new positions from one trial to the next. A schematic diagram of the experimental stimuli and the resulting perceptual interpretations are presented in Fig. 1A.


Effects of spatial and feature attention on disparity-rendered structure-from-motion stimuli in the human visual cortex.

Ip IB, Bridge H, Parker AJ - PLoS ONE (2014)

Stimuli and experimental paradigm.A: Structure-from-motion cylinders disambiguated by binocular disparity are perceived as rotating counter-clockwise (bottom left) or clockwise (bottom right) as controlled by the disparity of the right and left-wards moving surfaces (adapted from Dodd et al., 2001). B: Schematic diagram of the behavioral task used in the MRI-scanner, illustrating an example trial where attention is cued to the right side. For cued cylinders, participants reported whether the speed of rotation in the 1st and 2nd interval was different, while uncued cylinders were ignored.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4061053&req=5

pone-0100074-g001: Stimuli and experimental paradigm.A: Structure-from-motion cylinders disambiguated by binocular disparity are perceived as rotating counter-clockwise (bottom left) or clockwise (bottom right) as controlled by the disparity of the right and left-wards moving surfaces (adapted from Dodd et al., 2001). B: Schematic diagram of the behavioral task used in the MRI-scanner, illustrating an example trial where attention is cued to the right side. For cued cylinders, participants reported whether the speed of rotation in the 1st and 2nd interval was different, while uncued cylinders were ignored.
Mentions: Stimuli were structure-from-motion cylinders, each composed of a 5°×5° field of 125 white (57.5 cd/m2) and black (1.9 cd/m2) dots (0.2° size, anti-aliased for sub-pixel resolution) moving at a sinusoidal velocity and disparity profile in opposite directions around a vertical axis on a gray background (17.8 cd/m2). Cylinders were centered ±5.5° either side of the vertical midline and 4.5° below the horizontal fixation plane. The peak velocity and binocular disparity was at the midline of the cylinder and decreased towards the edges. A center-to-front disparity of 0.09° describes the absolute difference in degrees of visual angle between the nearest or farthest point of the cylinder to the fixation plane amounting to 0.09° positive and 0.09° negative disparity. A positive disparity corresponds to the rightwards surface moving in front of the fixation point and the leftwards surface behind. When viewed from the top, this generates the perception of counter-clockwise rotation. The reversed parameters generate clockwise rotation. Average angular rotation speed of cylinders ranged between 100°/s–177°/s, i.e. a dot would require between 2–3.6 s to complete a 360° rotation around the central axis. When a dot reached the edge of the cylinder, it was redrawn with the matching disparity and velocity gradient for dots moving in the opposite direction. Dots were plotted in randomly distributed positions: vertical positions were chosen homogenously along the height of the cylinder, and each dot position was slightly perturbed to prevent the appearance of a regular pattern of dots; horizontal positions were chosen to be homogenously distributed along 0–360° around the axis of the cylinder. The lifetime of individual dots was kept short to facilitate SFM-perception through motion and depth cues [10], [18], [19], [20]. On each video frame, 2% of the dots disappeared and were re-plotted in a random location on each video frame with a velocity appropriate to the new location. The dots of the cylinders were in new positions from one trial to the next. A schematic diagram of the experimental stimuli and the resulting perceptual interpretations are presented in Fig. 1A.

Bottom Line: Here we test whether this non-spatial component can co-select individual features that are perceptually bound into a coherent object.Our study used binocular disparity and visual motion to define disparity structure-from-motion (dSFM) stimuli.Our results demonstrate that feature and global feature attention effects are variable across participants, suggesting that the feature attention system may be limited in its ability to automatically select features within the attended object.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Anatomy & Genetics, University of Oxford, Oxford, United Kingdom; Nuffield Department of Clinical Neurosciences, The Oxford Centre for Functional Magnetic Resonance Imaging of the Brain, University of Oxford, Oxford, United Kingdom.

ABSTRACT
An important advance in the study of visual attention has been the identification of a non-spatial component of attention that enhances the response to similar features or objects across the visual field. Here we test whether this non-spatial component can co-select individual features that are perceptually bound into a coherent object. We combined human psychophysics and functional magnetic resonance imaging (fMRI) to demonstrate the ability to co-select individual features from perceptually coherent objects. Our study used binocular disparity and visual motion to define disparity structure-from-motion (dSFM) stimuli. Although the spatial attention system induced strong modulations of the fMRI response in visual regions, the non-spatial system's ability to co-select features of the dSFM stimulus was less pronounced and variable across subjects. Our results demonstrate that feature and global feature attention effects are variable across participants, suggesting that the feature attention system may be limited in its ability to automatically select features within the attended object. Careful comparison of the task design suggests that even minor differences in the perceptual task may be critical in revealing the presence of global feature attention.

Show MeSH
Related in: MedlinePlus