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Breana Carter, Paul Smith, Melanie Palomares; The effect of viewing eccentricity on visual enumeration. Journal of Vision 2011;11(11):1208. doi: 10.1167/11.11.1208.
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© ARVO (1962-2015); The Authors (2016-present)
Visual acuity and contrast sensitivity progressively diminish with increasing viewing eccentricity. Here we evaluated how visual enumeration is affected by visual eccentricity, and whether subitizing capacity, the accurate enumeration of a small number (<3–4) of items, decreases with more eccentric viewing. Participants enumerated gratings (0–9) presented for 50 ms along an imaginary circle at eccentricities of 2.25, 4.5, 6.75, 9 and 11.25 deg. We found that enumeration accuracies (proportion correct) decreased with increasing eccentricity. However, the subitzing capacity was constant at 3 items across all eccentricities except at 11.25 deg, where subitizing capacity was decreased to 2 items. We also analyzed the distribution of the responses. Mean responses as a function of number deviated from the unit slope as the gratings were presented at larger eccentricities. The coefficient of variation, a normalized metric of enumeration precision defined as the standard deviation divided by the mean (Palomares & Egeth, 2010), plotted against number of patches resulted in log-log slopes ranging from −.39 to −.65. Our results show that increasing viewing eccentricity makes enumeration less accurate, but that the critical features of enumeration functions are generally resistant to the effects of viewing eccentricity.
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