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Dennis Levi, Thom Carney; Crowding in peripheral vision: Why bigger is not always better. Journal of Vision 2009;9(8):982. doi: 10.1167/9.8.982.
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© ARVO (1962-2015); The Authors (2016-present)
Crowding, the deleterious influence of nearby contours on visual discrimination, is ubiquitous in spatial vision. Crowding impairs recognition of objects in clutter, and is thought to reflect inappropriate integration of target and flankers in peripheral vision. One prediction of the faulty integration model is that increasing the size of the flankers should result in increased crowding. We tested this hypothesis using a simple orientation discrimination task. The target was a Gabor patch, and the flankers were comprised of N segments (N = 1 to 8) of an annular grating. Strong threshold elevation occurred when the inner edge of the annulus was closer than about 0.4 times the target eccentricity. Control experiments (e.g. target detection, and radial/tangential asymmetries) verified that this threshold elevation was due to crowding rather than masking or surround suppression. Fixing the position of the inner edge and increasing the size of the annulus resulted in a monotonic decrease in the magnitude of crowding - i.e., the bigger the flanks, the smaller the crowding. To characterize this surprising result we: 1) fixed the annulus size and varied the target-flank distance, 2) fixed the outer edge of the annulus and varied its size. All three data sets superimposed when plotted as a function of the center-to-center distance between target and flanks. Taken together our results provide an explanation for the unexpected effect of flank size - increasing the annulus size (with a fixed inner radius) increased the center-to-center distance between target and flankers. The faulty integration model is indeed faulty. The results are consistent with the notion that the visual system extracts the centroids of features (both targets and flankers) within ≈ 0.4 times the target eccentricity, and jumbles them up into a crowded percept, so bigger is not necessarily better.
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