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I. Gottlob, A. Khanna, F.A. Proudlock; Scotopic and Photopic Perceptual Fading . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5351.
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Perceptual fading has been investigated extensively under photopic and mesopic conditions and varies with eccentricity and polar angle across the visual field. However, to our knowledge filling–in has never been investigated under scotopic conditions. We have compared scotopic and photopic perceptual fading at various eccentricities along horizontal and vertical meridians.
Fading times were recorded in 9 volunteers at 0°, 2.5°, 5°, 10° and 20° using isoluminant red–green stimuli and 5°, 10° and 20° under dark–adapted conditions. Detection thresholds were measured during dark adaptation, using the rod–cone break to ensure only rods were stimulated. Nasal, temporal, superior and inferior hemimeridians were compared. Previously described rod and cone densities were also compared.
A consistent anisotropy was evident for photopic stimuli, with horizontal meridians taking longer to fill–in than vertical targets (p=0.01). Fading times resembled previously described cone densities in the retina. All volunteers filled–in stimuli under dark adapted conditions, however, fading times did not resemble rod distributions in the retina. Instead, the ratio of fading time / rod density decreased with eccentricity.
We describe scotopic filling–in for the first time but find that it does not resemble patterns of photoreceptor densities as photopic perceptual fading does. Instead, scotopic filling–in is more rapid in the peripheral visual field in relation to rod density.
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