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Quan Lei, Adam Reeves; Lower in Contrast, Higher in Numerosity. Journal of Vision 2014;14(10):998. doi: https://doi.org/10.1167/14.10.998.
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© ARVO (1962-2015); The Authors (2016-present)
We report a new illusion in which there seem to be more grey disks than white disks when randomly-located white disks are intermingled with the same number of grey disks on a dark grey field. On a light grey field, there seem to be more dark grey than black disks. Of our 20 subjects, 19 experienced the illusion. Psychometric functions were obtained in a numerosity discrimination task to quantify the illusion with 30' arc disks on a 10 deg-wide dark-grey field. Functions were reliably steep. The 50% point (which varied systematically with grey level) indicated that, in the best case, 32 grey disks matched 50 white disks in numerosity - an illusion of 36%. When the white and grey disks were not intermingled the illusion disappeared. We also tested shape: when the white and grey stimuli had different shapes (squares and disks with equal area), the illusion decreased to 8%. We conclude that similarly-shaped elements of different contrasts compete such that the higher-contrast elements are surprisingly under-estimated relative to the lower-contrast ones. Possible explanations include: (1) higher-contrast disks are seen in front, potentially occluding hypothetical lower-contrast disks that are unseen yet estimated; (2) the attended disks, typically those with higher contrast, group more and so seem less numerous; and (3) when contrasts are close, some higher-contrast disks are assimilated to the lower-contrast disks.
Meeting abstract presented at VSS 2014
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