Limits...
Fovea-periphery axis symmetry of surround modulation in the human visual system.

Nurminen L, Kilpeläinen M, Vanni S - PLoS ONE (2013)

Bottom Line: We measured surround modulation of blood-oxygenation-level-dependent signal and perceived contrast with surrounds that extended either towards the periphery or the fovea from a center stimulus, centered at 6° eccentricity.This design compares the effects of two surrounds which are identical in visual field size, but differ in the sizes of their cortical representations.Although the fovea-periphery anisotropy affects nearly all aspects of spatial vision, our results suggest that in surround modulation the visual system compensates for it.

View Article: PubMed Central - PubMed

Affiliation: Brain Research Unit, O.V. Lounasmaa Laboratory, Aalto University, Espoo, Finland. lnurmin@neuro.hut.fi

ABSTRACT
A visual stimulus activates different sized cortical area depending on eccentricity of the stimulus. Here, our aim is to understand whether the visual field size of a stimulus or cortical size of the corresponding representation determines how strongly it interacts with other stimuli. We measured surround modulation of blood-oxygenation-level-dependent signal and perceived contrast with surrounds that extended either towards the periphery or the fovea from a center stimulus, centered at 6° eccentricity. This design compares the effects of two surrounds which are identical in visual field size, but differ in the sizes of their cortical representations. The surrounds produced equally strong suppression, which suggests that visual field size of the surround determines suppression strength. A modeled population of neuronal responses, in which all the parameters were experimentally fixed, captured the pattern of results both in psychophysics and functional magnetic resonance imaging. Although the fovea-periphery anisotropy affects nearly all aspects of spatial vision, our results suggest that in surround modulation the visual system compensates for it.

Show MeSH

Related in: MedlinePlus

V1 BOLD signal reduction as a function of the gap size.a) Results of the voxel-of-interest analysis. Connected data points mark the mean ± s.e.m. averaged over seven subjects. Dashed lines present suppression strength in the modeled neuronal population in which all parameters were fixed based on the area summation experiment. b) Modeled responses in the voxel-of-interest for surround stimulus displayed without the center. The gray horizontal line marks the baseline response c) Results of the region-of-interest analysis.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3585267&req=5

pone-0057906-g004: V1 BOLD signal reduction as a function of the gap size.a) Results of the voxel-of-interest analysis. Connected data points mark the mean ± s.e.m. averaged over seven subjects. Dashed lines present suppression strength in the modeled neuronal population in which all parameters were fixed based on the area summation experiment. b) Modeled responses in the voxel-of-interest for surround stimulus displayed without the center. The gray horizontal line marks the baseline response c) Results of the region-of-interest analysis.

Mentions: The purpose of the first fMRI experiment was to find out whether suppression strength is determined by visual field size rather than cortical size of the surround already at the level of V1. Figure 4a shows the results of the voxel-of-interest analysis. The analysis concerns the signals from a single voxel, situated nearest to the geometric center of the activation produced by the independent functional localizer. When the gap size was small, both the inward and the outward surrounds strongly reduced the center signal and increasing the gap size decreased BOLD signal reduction. As the gap size of the inward surround was increased from 0.1 to 1.8°, the mean BOLD signal reduction decreased from 29.9±9.0% to 3.1±5.0% (paired two-tailed t-test, t(6) = 3.48, p<0.05). For the outward surround condition, the corresponding decrease was from 25.6±9.0% to −0.7±3.8% (t(6) = 3.13, p<0.05). The BOLD signal reduction did not differ statistically significantly between the inward and the outward surrounds at any of the gap sizes (paired two-tailed t-tests, gap 0.1°, t(6) = −0.45, p = 0.67; gap 0.6°, t(6) = 0.86, p = 0.42; gap 1.8°, t(6) = −0.64, p = 0.55).


Fovea-periphery axis symmetry of surround modulation in the human visual system.

Nurminen L, Kilpeläinen M, Vanni S - PLoS ONE (2013)

V1 BOLD signal reduction as a function of the gap size.a) Results of the voxel-of-interest analysis. Connected data points mark the mean ± s.e.m. averaged over seven subjects. Dashed lines present suppression strength in the modeled neuronal population in which all parameters were fixed based on the area summation experiment. b) Modeled responses in the voxel-of-interest for surround stimulus displayed without the center. The gray horizontal line marks the baseline response c) Results of the region-of-interest analysis.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3585267&req=5

pone-0057906-g004: V1 BOLD signal reduction as a function of the gap size.a) Results of the voxel-of-interest analysis. Connected data points mark the mean ± s.e.m. averaged over seven subjects. Dashed lines present suppression strength in the modeled neuronal population in which all parameters were fixed based on the area summation experiment. b) Modeled responses in the voxel-of-interest for surround stimulus displayed without the center. The gray horizontal line marks the baseline response c) Results of the region-of-interest analysis.
Mentions: The purpose of the first fMRI experiment was to find out whether suppression strength is determined by visual field size rather than cortical size of the surround already at the level of V1. Figure 4a shows the results of the voxel-of-interest analysis. The analysis concerns the signals from a single voxel, situated nearest to the geometric center of the activation produced by the independent functional localizer. When the gap size was small, both the inward and the outward surrounds strongly reduced the center signal and increasing the gap size decreased BOLD signal reduction. As the gap size of the inward surround was increased from 0.1 to 1.8°, the mean BOLD signal reduction decreased from 29.9±9.0% to 3.1±5.0% (paired two-tailed t-test, t(6) = 3.48, p<0.05). For the outward surround condition, the corresponding decrease was from 25.6±9.0% to −0.7±3.8% (t(6) = 3.13, p<0.05). The BOLD signal reduction did not differ statistically significantly between the inward and the outward surrounds at any of the gap sizes (paired two-tailed t-tests, gap 0.1°, t(6) = −0.45, p = 0.67; gap 0.6°, t(6) = 0.86, p = 0.42; gap 1.8°, t(6) = −0.64, p = 0.55).

Bottom Line: We measured surround modulation of blood-oxygenation-level-dependent signal and perceived contrast with surrounds that extended either towards the periphery or the fovea from a center stimulus, centered at 6° eccentricity.This design compares the effects of two surrounds which are identical in visual field size, but differ in the sizes of their cortical representations.Although the fovea-periphery anisotropy affects nearly all aspects of spatial vision, our results suggest that in surround modulation the visual system compensates for it.

View Article: PubMed Central - PubMed

Affiliation: Brain Research Unit, O.V. Lounasmaa Laboratory, Aalto University, Espoo, Finland. lnurmin@neuro.hut.fi

ABSTRACT
A visual stimulus activates different sized cortical area depending on eccentricity of the stimulus. Here, our aim is to understand whether the visual field size of a stimulus or cortical size of the corresponding representation determines how strongly it interacts with other stimuli. We measured surround modulation of blood-oxygenation-level-dependent signal and perceived contrast with surrounds that extended either towards the periphery or the fovea from a center stimulus, centered at 6° eccentricity. This design compares the effects of two surrounds which are identical in visual field size, but differ in the sizes of their cortical representations. The surrounds produced equally strong suppression, which suggests that visual field size of the surround determines suppression strength. A modeled population of neuronal responses, in which all the parameters were experimentally fixed, captured the pattern of results both in psychophysics and functional magnetic resonance imaging. Although the fovea-periphery anisotropy affects nearly all aspects of spatial vision, our results suggest that in surround modulation the visual system compensates for it.

Show MeSH
Related in: MedlinePlus