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Area summation in human vision at and above detection threshold.

Meese TS, Summers RJ - Proc. Biol. Sci. (2007)

Bottom Line: To overcome this confound, a novel stimulus class is designed where: (i) the observer operates on a constant retinal area, (ii) the target area is controlled within this summation field, and (iii) the pedestal is fixed in size.Using this arrangement, substantial summation is found along the entire masking function, including the region of facilitation.Our analysis shows that PS and uncertainty cannot account for the results, and that suprathreshold summation of contrast extends over at least seven target cycles of grating.

View Article: PubMed Central - PubMed

Affiliation: School of Life and Health Sciences, Aston University, Birmingham B47ET, UK. t.s.meese@aston.ac.uk

ABSTRACT
The initial image-processing stages of visual cortex are well suited to a local (patchwise) analysis of the viewed scene. But the world's structures extend over space as textures and surfaces, suggesting the need for spatial integration. Most models of contrast vision fall shy of this process because (i) the weak area summation at detection threshold is attributed to probability summation (PS) and (ii) there is little or no advantage of area well above threshold. Both of these views are challenged here. First, it is shown that results at threshold are consistent with linear summation of contrast following retinal inhomogeneity, spatial filtering, nonlinear contrast transduction and multiple sources of additive Gaussian noise. We suggest that the suprathreshold loss of the area advantage in previous studies is due to a concomitant increase in suppression from the pedestal. To overcome this confound, a novel stimulus class is designed where: (i) the observer operates on a constant retinal area, (ii) the target area is controlled within this summation field, and (iii) the pedestal is fixed in size. Using this arrangement, substantial summation is found along the entire masking function, including the region of facilitation. Our analysis shows that PS and uncertainty cannot account for the results, and that suprathreshold summation of contrast extends over at least seven target cycles of grating.

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Related in: MedlinePlus

Area summation results from experiment 1 and model predictions (thick curves). Error bars show ±1 s.e. The inset shows the weighting function of the filter used in the modelling. The abscissa refers to the area bounded by the outer edge of the stimulus plateau. The dotted lines are fiducial contours with slopes of −1/2 and −1/4. The thin curve beneath the open squares is described in the Discussion.
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fig2: Area summation results from experiment 1 and model predictions (thick curves). Error bars show ±1 s.e. The inset shows the weighting function of the filter used in the modelling. The abscissa refers to the area bounded by the outer edge of the stimulus plateau. The dotted lines are fiducial contours with slopes of −1/2 and −1/4. The thin curve beneath the open squares is described in the Discussion.

Mentions: The filled circles in figure 2 show area summation for the full stimulus, which is a bowed function of stimulus area. The initial part of the function approximates a slope of m′=−1/2 on these double-log coordinates. The intermediate region is shallower and approximates a slope of m′=−1/4, but becomes asymptotic thereafter. This general form is similar to that found in previous studies, where area summation has been measured in the central visual field (Tootle & Berkley 1983; Garcia-Perez 1988; Rovamo et al. 1993; Foley et al. 2007).


Area summation in human vision at and above detection threshold.

Meese TS, Summers RJ - Proc. Biol. Sci. (2007)

Area summation results from experiment 1 and model predictions (thick curves). Error bars show ±1 s.e. The inset shows the weighting function of the filter used in the modelling. The abscissa refers to the area bounded by the outer edge of the stimulus plateau. The dotted lines are fiducial contours with slopes of −1/2 and −1/4. The thin curve beneath the open squares is described in the Discussion.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2211515&req=5

fig2: Area summation results from experiment 1 and model predictions (thick curves). Error bars show ±1 s.e. The inset shows the weighting function of the filter used in the modelling. The abscissa refers to the area bounded by the outer edge of the stimulus plateau. The dotted lines are fiducial contours with slopes of −1/2 and −1/4. The thin curve beneath the open squares is described in the Discussion.
Mentions: The filled circles in figure 2 show area summation for the full stimulus, which is a bowed function of stimulus area. The initial part of the function approximates a slope of m′=−1/2 on these double-log coordinates. The intermediate region is shallower and approximates a slope of m′=−1/4, but becomes asymptotic thereafter. This general form is similar to that found in previous studies, where area summation has been measured in the central visual field (Tootle & Berkley 1983; Garcia-Perez 1988; Rovamo et al. 1993; Foley et al. 2007).

Bottom Line: To overcome this confound, a novel stimulus class is designed where: (i) the observer operates on a constant retinal area, (ii) the target area is controlled within this summation field, and (iii) the pedestal is fixed in size.Using this arrangement, substantial summation is found along the entire masking function, including the region of facilitation.Our analysis shows that PS and uncertainty cannot account for the results, and that suprathreshold summation of contrast extends over at least seven target cycles of grating.

View Article: PubMed Central - PubMed

Affiliation: School of Life and Health Sciences, Aston University, Birmingham B47ET, UK. t.s.meese@aston.ac.uk

ABSTRACT
The initial image-processing stages of visual cortex are well suited to a local (patchwise) analysis of the viewed scene. But the world's structures extend over space as textures and surfaces, suggesting the need for spatial integration. Most models of contrast vision fall shy of this process because (i) the weak area summation at detection threshold is attributed to probability summation (PS) and (ii) there is little or no advantage of area well above threshold. Both of these views are challenged here. First, it is shown that results at threshold are consistent with linear summation of contrast following retinal inhomogeneity, spatial filtering, nonlinear contrast transduction and multiple sources of additive Gaussian noise. We suggest that the suprathreshold loss of the area advantage in previous studies is due to a concomitant increase in suppression from the pedestal. To overcome this confound, a novel stimulus class is designed where: (i) the observer operates on a constant retinal area, (ii) the target area is controlled within this summation field, and (iii) the pedestal is fixed in size. Using this arrangement, substantial summation is found along the entire masking function, including the region of facilitation. Our analysis shows that PS and uncertainty cannot account for the results, and that suprathreshold summation of contrast extends over at least seven target cycles of grating.

Show MeSH
Related in: MedlinePlus