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Holly E. Gerhard, Laurence T. Maloney; Albedo perturbation detection under illumination transformations: A dynamic analogue of lightness constancy. Journal of Vision 2008;8(6):289. doi: 10.1167/8.6.289.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose. Everyday scenes are typically illuminated by multiple light sources (sun, sky). Changes in the position/intensity of neutral light sources can induce complex transformations of luminances associated with achromatic surfaces in the scene. Last year we presented evidence that observers can accurately discriminate the transformations induced by small changes in direction of a collimated source from transformations matched in edge-ratio information and global image statistics. This year we evaluate whether this ability aids in detection of simultaneous albedo perturbations, a dynamic analogue of lightness constancy. Methods. The stimuli were stereoscopically presented renderings of 8 concave or convex pyramids with random heights and facet albedo patterns. Two frames were presented in which the scene underwent a global luminance transformation induced by a change in collimated source position of 15 degrees (light change) or a matched, scrambled version of the same transformation (non-light change). From frame one to two, one pyramid facet might undergo an additional change: an albedo perturbation of ±20, ±30, ±40, or ±50%. Albedo changes occurred with 50% probability, with 400 trials total at each level for both global change types (3200 trials total). On each trial, observers judged whether an albedo change occurred. Feedback was not given. Analysis. We estimated d' estimates separately for light and non-light changes at each perturbation level. Results: Albedo perturbation detection was significantly more sensitive under light changes than under non-light changes (t=10.74; p Conclusion: Observers can more accurately detect changes in surface albedo against a background of global change in surface luminance when the pattern of change of luminance is consistent with change of position of a collimated light source in the scene, a dynamic analogue of lightness constancy.
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