Agostini & Bruno (Perception & Psychophysics in press) showed that the size of simultaneous lightness contrast effect measured under homogenous illumination doubles under Gelb lighting; that is, an illumination border is made to coincide with the outer border of the display, and the rest of the visual field is left in near darkness. According to the authors this effect is due to the spatial distribution of illumination. Gilchrist et al (to be published) propose a more detailed explanation. According to this theory, the doubling of the contrast effect results from a compromise between predictions made in relation to two competing frameworks, local and global. To test this hypothesis, we manipulated the relative weight of the two frameworks. The experimental display consisted of a middle gray surface on a black background and of a Munsell scale (16 steps from black to white) on a white background. The two backgrounds were suspended in mid-air but they where not adjacent. In the experiment, we gradually changed the luminance ratio between the experimental display and the rest of the visual field. Observers chose the closest match on the Munsell scale for each of the selected luminance ratios. In support of Gilchrist et al's explanation, the larger increase of contrast measured by Agostini and Bruno is reached only within a narrow range of luminance ratios.
Influence of the context on simultaneous lightness contrast
GALMONTE, Alessandra
1996-01-01
Abstract
Agostini & Bruno (Perception & Psychophysics in press) showed that the size of simultaneous lightness contrast effect measured under homogenous illumination doubles under Gelb lighting; that is, an illumination border is made to coincide with the outer border of the display, and the rest of the visual field is left in near darkness. According to the authors this effect is due to the spatial distribution of illumination. Gilchrist et al (to be published) propose a more detailed explanation. According to this theory, the doubling of the contrast effect results from a compromise between predictions made in relation to two competing frameworks, local and global. To test this hypothesis, we manipulated the relative weight of the two frameworks. The experimental display consisted of a middle gray surface on a black background and of a Munsell scale (16 steps from black to white) on a white background. The two backgrounds were suspended in mid-air but they where not adjacent. In the experiment, we gradually changed the luminance ratio between the experimental display and the rest of the visual field. Observers chose the closest match on the Munsell scale for each of the selected luminance ratios. In support of Gilchrist et al's explanation, the larger increase of contrast measured by Agostini and Bruno is reached only within a narrow range of luminance ratios.
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