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Denis Pelli; Despite a 100-fold drop in cortical magnification, a fixed-size letter is recognized equally well at eccentricities of 0 to 20 deg. How can this be?. Journal of Vision 2018;18(10):26. doi: 10.1167/18.10.26.
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Formerly, peripheral vision has been modeled as central vision scaled by the cortical magnification (Virsu & Rovamo, 1979). That model is rejected by finding conservation across eccentricity of recognition of a fixed-size target. We find that efficiency and equivalent noise are conserved across 0 to 20 deg eccentricity. (Based on measured threshold contrast for identification of brief Sloan letter, with and without noise, using method of Pelli & Farell, 1999.) Thus, human ability to recognize a simple target is surprisingly immune to cortical magnification, and the neurons per deg2. Of course, if more targets are introduced, they crowd each other, unless separated by at least the crowding distance, which is inversely proportional to the cortical magnification (Pelli, 2008). The literature on crowding suggests that the area within the crowding distance in all directions feeds a recognition unit that can recognize a simple object (but not two) independent of its position in the unit's area. The conservation of recognition reported here implies that the larger (peripheral) recognition units recognize a fixed-size target just as well as the smaller (central) units, despite a 10,000-fold change in area from 0 to 20 deg. Instead of the Virsu & Rovamo scaling model, here we find that the recognition units implied by crowding vary in size but all recognize a fixed-size target equally well.
Meeting abstract presented at VSS 2018
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