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Kimberley Halen, Igor Juricevic, Kyle McDermott, Michael A. Webster; Variations in achromatic settings across the visual field. Journal of Vision 2010;10(7):394. doi: 10.1167/10.7.394.
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© ARVO (1962-2015); The Authors (2016-present)
The stimulus spectrum that appears white shows little change between the fovea and near periphery, despite large changes in spectral sensitivity from differences in macular pigment screening (Beer et al JOV 2005; Webster and Leonard JOSA A 2008). This perceptual constancy could occur if color coding at different regions of the retina is normalized to the local average spectrum. However, local adaptation could instead lead to changes in the achromatic point across the visual field if the spectral characteristics of the world itself vary across space. Natural scenes in fact include significant spatial variations in chromaticity because of factors such as the spectral differences between earth and sky. We asked whether there might be corresponding differences in achromatic loci in upper and lower visual fields. Observers dark adapted and then viewed a 25 cd/m2 2-deg spot flashed repeatedly for 0.5 sec on and 3.5 sec off on a black background. The chromaticity of the spot was adjusted to appear achromatic by using a pair of buttons that varied chromaticities in terms of the CIE u′v′ coordinates. Settings were repeated while observers fixated dim markers so that the spot fell at a range of eccentricities spanning +60 deg along the vertical meridian. Achromatic settings did not change systematically with location, and in particular did not show a blue to yellow-green trend consistent with outdoor scenes. This could indicate that observers are primarily adapted to environments with more stationary color statistics (e.g. indoor settings) or that achromatic loci are also calibrated by retinally non-local processes.
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