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Torsten Strasser, Hana Langrová, Laura Kuehlewein, Annette Werner, Anne Kurtenbach, Eberhart Zrenner; THEY CAN DISAPPEAR - Can the panda illusion be used to test visual acuity?. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4216.
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© ARVO (1962-2015); The Authors (2016-present)
In 2016, the artist Ilja Klemencov revealed the artwork “They can disappear” (Fig. 1), pointing out the danger of extinction of the panda bear. The illustration shows the WWF logo, a panda, hidden behind black-and-white zigzagged lines. Many people struggle to spot the bear at a first glance. However, stepping back or taking off the glasses unveils the panda. This lead us to the question if the ability to see the panda is related to the observer's VA and if therefore, the panda illusion can be used to test visual acuity.
Images were dynamically created using silhouettes of 6 animals and presented in random order on a high-resolution screen using PsychoPy. For each presentation, he spatial frequency of the zigzag pattern was adapted based on the subjects’ response using an adaptive staircase method (Kaernbach 1991). The test ended when the limiting spatial frequency, that allows for correct identification of the animals, was determined.23 subjects (16 ♂, 7 ♀, 38±16 yrs.) with normal ophthalmic exam (BCVA ≥ 1.0), were recruited. All subjects underwent the test with BCVA and with artificially degraded VA using plus lenses (+1D, +2D) and Bangerter occlusion foils (0.6, 0.2). Additionally, VA was determined for each condition using the Landolt C-FrACT test.
Simple linear regressions were calculated to predict VA based on the limiting spatial frequency for BCVA and artificially degraded VA. Significant regression equations were found for both, plus lenses (F(1, 63) = 78.44, p < .0001, R2 = .555), and Bangerter foils (F(1, 63) = 44.53, p < .0001, R2 = .414). VA increased 0.32 (plus lenses) and 0.27 (Bangerter), respectively, for each cycle of degree of the limiting spatial frequency.
We found a significant correlation between the limiting spatial frequency and the visual acuity. However, the variability of the predicted VA is rather wide. The illusion may not be completely explained by the VA alone. Other contributing factors may be the point spread function or visual crowding. Nevertheless, the counterintuitive application of this illusion and the simplicity of the test may render it useful for estimating the visual acuity.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
Fig. 1: “They can disappear” by Ilja Klemencov. Many people struggle to spot the panda of the WWF logo at a first glance. The artist uses the intriguing effect of this optical illusion to point out the danger of extinction of the panda bear.
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