Spatial frequency sensitivity does not explain the reduction in perceived numerosity in the peripheral visual field. M Valsecchi, M Toscani, K R Gegenfurtner |
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Abteilung Allgemeine Psychologie, Justus-Liebig Universität Giessen, Germany
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| When human observers are asked to judge the number of elements in a peripheral crowd, their estimates are reduced compared to foveal presentation [Valsecchi et al, 2012, Perception, 41 ECVP Supplement, 128]. In the present contribution we investigate whether this effect is explained by the differential spatial frequency sensitivity, in the light of the proposal that a ratio of high to low spatial frequency channel output is used to estimate numerosity [Dakin et al. 2011, PNAS, 108]. We constructed filtered images of our dot arrays devised so as to produce comparable channel outputs centrally and peripherally. First we decomposed our arrays into 8 images with power concentrated at increasing spatial frequencies. Subsequently we measured peripheral and foveal detection thresholds for each component image and recombined them after weighting each image by its detection threshold. When judging the numerosity of such filtered images our observers still exhibited the reduction (around 10%) in peripheral numerosity we observed with the original images, excluding a simple explanation in terms of spatial frequency sensitivity. We suggest numerosity in the peripheral visual field is computed from channels tuned to a lower spatial frequency rather than from channels with the same spatial frequency tuning but lower sensitivity. |
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