Area summation in human vision at and above detection threshold


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. © 2007 The Royal Society.

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Divisions: College of Health & Life Sciences > School of Optometry > Optometry
College of Health & Life Sciences > Clinical and Systems Neuroscience
College of Health & Life Sciences > School of Optometry > Centre for Vision and Hearing Research
Uncontrolled Keywords: contrast gain control,dipper function,psychophysics,spatial summation,suppression,Agricultural and Biological Sciences(all),Agricultural and Biological Sciences (miscellaneous)
Publication ISSN: 1471-2954
Last Modified: 13 Feb 2024 08:04
Date Deposited: 10 Nov 2010 13:20
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Related URLs: http://www.scop ... tnerID=8YFLogxK (Scopus URL)
http://rspb.roy ... /1627/2891.full (Publisher URL)
PURE Output Type: Article
Published Date: 2007-11-22
Authors: Meese, Timothy S. (ORCID Profile 0000-0003-3744-4679)
Summers, Robert J, (ORCID Profile 0000-0003-4857-7354)



Version: Published Version

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