September 2017
Volume 17, Issue 10
Open Access
Vision Sciences Society Annual Meeting Abstract  |   August 2017
The fusional range of the periphery
Author Affiliations
  • Saeideh Ghahghaei
    The Smith-Kettlewell Eye Research Institute
  • Suzanne McKee
    The Smith-Kettlewell Eye Research Institute
  • Preeti Verghese
    The Smith-Kettlewell Eye Research Institute
Journal of Vision August 2017, Vol.17, 1058. doi:10.1167/17.10.1058
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      Saeideh Ghahghaei, Suzanne McKee, Preeti Verghese; The fusional range of the periphery. Journal of Vision 2017;17(10):1058. doi: 10.1167/17.10.1058.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

We investigated how the fusional range scales with eccentricity. Specifically, we measured the fusional range in the fovea and at 10 degrees below fixation. The limits of Panum's area are usually measured by increasing the disparity until the target appears "fuzzy". This is a poor method for the periphery as targets often appear fuzzy, even when presented with zero disparity. Here, we used a more rigorous method to determine the uppermost limit of fusion. At long durations, the two half-images that define a large disparity appear as two isolated targets in the same flat plane; small incremental changes in disparity produce changes in the separation between the half-images and disparity magnitude can be judged on the basis of separation, just like a monocular width judgment. The fusion limit is the point at which the threshold for judging dichoptic separation between the half-images is equal to the width threshold for monocular targets with the same separation. The targets were two patches of dynamic random dots. For dichoptic viewing, the reference target was presented in the fixation plane while the test target had a standing pedestal disparity. Participants made incremental judgments of disparity around this pedestal. For monocular presentation, two patches were shown to one eye and participants judged the width between the targets. Thresholds for incremental disparity and width discrimination were plotted as a function of the pedestal disparity or width. For both fovea and periphery, dichoptic thresholds initially increased with pedestal and then decreased until they matched the monocular thresholds. The fusional range at 10 degrees was a factor of 2-4 times larger than the fovea - smaller than eccentricity scaling for cortical magnification (5-6) or for hyperacuity (10 – 15). Our estimate is consistent with Ogle's (1954)'s estimate of fusion at 10 deg along the horizontal meridian.

Meeting abstract presented at VSS 2017

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