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Christopher R. L. Cantor, Humza J. Tahir, Clifton M. Schor; Is the Rotating Snakes an Optical Illusion?. Journal of Vision 2010;10(7):824. doi: https://doi.org/10.1167/10.7.824.
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© ARVO (1962-2015); The Authors (2016-present)
The “rotating snakes” (Kitoaka 2003) is a well-known illusion in which a static image of a repetitive pattern moves as it is examined during free viewing (the apparent movement ceases after several seconds of stable fixation). We have discovered that it is possible to eliminate this illusion by viewing the image through either a pinhole or defocused by a +2D plus lens.
We posit a largely optical, rather than neural, explanation of the effect. The optics of the eye are not uniform over visual space nor stationary over time. Under natural viewing conditions (>3mm pupil) the MTF varies significantly when measured at different visual eccentricities. Fluctuations in accommodation create temporal variations in the magnitude of defocus of the retinal image. Viewing the image through pinholes or a plus lens produces a uniformity in the MTF regardless of eccentricity, and also reduces or eliminates the impact of temporal fluctuation of accommodation on retinal image quality.
The “rotating snakes” illusion can be viewed online at http://www.ritsumei.ac.jp/~akitaoka/rotsnake.gif.
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