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Sharif Saleki, Marvin Maechler, Patrick Cava-nagh, Peter Tse; The magnitude of the Double-Drift illusion is lessened by a reference object with high positional certainty. Journal of Vision 2019;19(10):99a. doi: https://doi.org/10.1167/19.10.99a.
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© ARVO (1962-2015); The Authors (2016-present)
In the double-drift illusion (Lisi & Cavanagh, 2015; aka, curveball illusion: Shapiro et al., 2010; infinite regress illusion: Hsieh and Tse, 2006) a Gabor patch moves in one direction in the periphery while its internal texture moves in the orthogonal direction. In this case, the perceived path deviates dramatically from the physical path. To study the effect of an anchoring object on the magnitude of illusion, a single line with high positional certainty (boundary line) was placed parallel to the gabor’s physical path at different distances from it. During each trial, a boundary line was presented at a random position ranging from 2.5 degrees distance to the left or right of the gabor. Following the presentation, participants adjusted a single line at fixation to match the angle of the gabor’s perceived path. Fitting a linear regression model with distance as a predictor to each participant’s reported angles and comparing the slopes against zero showed that as the boundary line approached the gabor, it significantly reduced the magnitude of the perceived illusion. This suggests that the double-drift illusion is dependent on the positional uncertainty of the gabor patch (driven by the Guassian mask, eccentricity, contrast, spatial frequency, etc.) and that an anchoring reference can reduce this uncertainty and therefore reduce the illusion.
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