Surround articulation I Brightness judgments

It has been hypothesized that brightness judgments require an estimate of the illuminant. Making this estimate is difficult since luminance edges can be the result of changes in either illumination or reflectance. Articulation is the addition of equally spaced incremental and decremental patches within a surround while preserving the surround's space-average luminance. It is proposed that articulation enhances the inference that the surround's luminance edge is due to a change in illumination rather than in reflectance. Articulation results in a corresponding shift in brightness judgments for test-patch increments but not for decrements. This finding concurs with Arend and Goldstein's [J. Opt. Soc. Am. A 4, 2281 (1987)] reported shifts in brightness as simple center-surround stimuli are transformed into more complex ecologically valid Mondrians.