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Steven Dakin, Samuel Schwarzkopf, Geraint Rees, Catherine Morgan, Elaine Anderson; Cortical magnification factor of human V2 predicts individual susceptibility to letter-crowding. Journal of Vision 2017;17(10):396. doi: https://doi.org/10.1167/17.10.396.
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© ARVO (1962-2015); The Authors (2016-present)
Our peripheral vision is fundamentally limited by our inability to recognise objects when they appear within "clutter", a phenomenon known as crowding. Although widely studied, the cortical locus of this phenomenon remains unclear. This is in part because it is difficult to distinguish neural activity arising from a change in the stimulus (e.g. from introducing clutter) from activity associated with the resulting crowding. Here we overcome this by quantifying individual differences in susceptibility to crowding and correlate this with parameter estimates of cortical architecture, assessed using population receptive field (pRF) analysis of human fMRI data. We report that a simple psychophysical index of 'crowding susceptibility ' (the ratio of acuity for an isolated letter versus a crowded letter) is highly correlated with individual estimates of cortical magnification factor (CMF) in visual areas V2 and V3. This is strong evidence that V2/V3 plays a crucial role in setting the spatial scale of crowding and, as has been noted in several complementary psychophysical and computational studies, is consistent both with the receptive field (RF) and shape-encoding properties of cells within these areas.
Meeting abstract presented at VSS 2017
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