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Alejandro H. Gloriani, Alexander C. Schütz; Humans trust central vision more in the light and the dark. Journal of Vision 2019;19(10):67a. doi: https://doi.org/10.1167/19.10.67a.
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© ARVO (1962-2015); The Authors (2016-present)
To make optimal perceptual decisions, the visual system requires knowledge about its own properties and the relative reliability of signals arriving from different parts of the visual field. In the human retina, these signals come from two types of photoreceptors: cones, active under bright daylight illumination (photopic viewing) and highly concentrated in the fovea; and rods, active under dim illumination at night (scotopic viewing) and absent from the fovea (scotopic foveal scotoma). It is unclear if the scotopic foveal scotoma is filled-in and if humans can take into account the differences between scotopic and photopic vision when making perceptual decisions. We investigated the preference for central and peripheral vision under scotopic and photopic viewing. Stimuli consisted of a striped center (smaller than the foveal scotoma) and surround, which could have the same (continuous) or the orthogonal (discontinuous) orientation. In each trial two stimuli were presented. In Experiment 1, observers had to indicate which stimulus appeared continuous or discontinuous (half of the observers each). In Experiment 2, observers had to make two decisions: first they had to select which of the two stimuli they want to judge and then they had to report if this selected stimulus was continuous or discontinuous. We found that a stimulus with a discontinuity in the scotopic foveal scotoma appeared as continuous, providing evidence for perceptual filling-in. We also found that observers preferred information from central vision under photopic viewing and even when it was not veridical and only inferred under scotopic viewing. This general preference for central vision indicates that humans are not aware of their scotopic foveal scotoma and that it is not taken into account for perceptual decision making. This suggests that filling-in precedes the estimation of confidence, thereby shielding awareness from the foveal scotoma with respect to its contents and its properties.
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