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Francesca Fortenbaugh, Michael Silver, Lynn Robertson; Redefining the Metric of Visual Space: Visual Field Boundaries Influence Attentional Resolution and Crowding Performance. Journal of Vision 2013;13(9):577. doi: https://doi.org/10.1167/13.9.577.
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© ARVO (1962-2015); The Authors (2016-present)
Perceptual asymmetries exist for a variety of tasks. Here we show that one such asymmetry is explained by a new metric of visual space that is based on an individual’s visual field borders. Sixteen subjects performed a crowding task in which they were required to judge the orientation of a grating presented above or below fixation, either alone or flanked by four similar gratings. Previous studies have shown that participants are better at judging the orientation of the crowded grating along the lower vertical meridian than the upper vertical meridian. It has been theorized that this asymmetry is due to differences in the resolving power of spatial attention that are biased toward the lower field due to ecological factors. However, the upper and lower visual fields are asymmetrically bounded, with upper visual field extents (VFE) smaller than lower VFE. The metric we propose takes this anatomical asymmetry into account, replacing degrees of visual angle with a distance measure that is relative to VFE for a given radial direction, termed percentage of visual field extent (%VFE). To assess whether this metric could account for perceptual asymmetries, we measured each participant’s upper and lower VFE and used these values to compute %VFE for the 20° grating locations. The crowding displays were then presented at 20° above/below fixation and at matched locations (in units of %VFE) in the opposite hemifield. We found that the asymmetry in crowding performance was largely accounted for by individual variability in visual field extent (R[sup]2[/sup]=0.54). Importantly, this asymmetry is eliminated when the locations of stimuli are equated using the new metric (i.e., locations with equal %VFE). These results challenge the assumption that degrees of visual angle is the most appropriate metric for visual space and suggest that attentional resolution in crowding is more symmetric than previously thought.
Meeting abstract presented at VSS 2013
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