S. Nishida and M. Shinya (1998) found that observers have only a limited ability to recover surface-reflectance properties under changes in surface shape. Our aim in the present study was to investigate how the degree of surface-reflectance constancy depends on the availability of information that may help to infer the reflectance and shape properties of surfaces. To this end, we manipulated the availability of (i) motion-induced information (static vs. dynamic presentation), (ii) disparity information (with the levels "monocular," "surface disparity," and "surface + highlight disparity"), and (iii) color information (grayscale stimuli vs. hue differences between diffuse and specular reflections). The task of the subjects was to match the perceived lightness and glossiness between two surfaces with different spatial frequency and amplitude by manipulating the diffuse component and the exponent of the Phong lighting model in one of the surfaces. Our results indicate that all three types of information improve the constancy of glossiness matches--both in isolation and in combination. The lightness matching data only revealed an influence of motion and color information. Our results indicate, somewhat counterintuitively, that motion information has a detrimental effect on lightness constancy.
The disparity of highlights on specular reflecting surfaces usually differs from the disparity of the surface points. A. Kirschmann (1895) proposed that this fact may be used as a binocular cue for gloss perception. This was confirmed by A. Blake and H. Bülthoff (1990) who found that subjects judged the glossiness of convex ellipsoidal surfaces as most realistic if the disparity of the highlights was close to the physical correct one. Extending on this finding, we investigate more closely whether the effect of highlight disparity depends on the sharpness of the highlight and the relative amount of diffuse and specular reflection. We measured the effect of highlight disparity on both perceived strength and perceived authenticity of gloss. We used complex, three-dimensional curved surfaces that were stereoscopically presented on a CRT. The reflection characteristics were varied using the Phong lighting model. Highlights were presented either with or without highlight disparity. In a rating experiment, subjects were asked to judge the strength and the authenticity of the perceived surface glossiness. The presence of highlight disparity lead to an enhancement of both the authenticity and the strength of perceived glossiness. The latter finding was confirmed in an additional matching experiment.
R. O. Brown and D. I. MacLeod (1997) observed that chromatic patches appear much more saturated against an equiluminant, uniform gray surround than against a chromatically variegated surround with the same space-average color. Using asymmetric color matching, we investigated what stimulus conditions are critical for the occurrence of this "gamut expansion effect." We found (a) that the effect diminishes rapidly with increasing color contrast between target and surround, (b) that the amount and the spatial distribution of color variance in the surround plays but a very limited role, (c) that the effect is mainly local, and (d) that basically the same effect can be obtained by comparing two uniform surrounds. These findings, particularly the latter, argue strongly against an explanation solely in terms of contrast adaptation. We suggest that the main features of our findings can be explained in terms of color scission.
We present the results of an experiment aiming to clarify the relation between simultaneous colour contrast and Brown and MacLeod's (1997) gamut expansion effect. These two context effects are often thought to be due to two different mechanisms, but this assumption has not previously been subjected to empirical test. Here we used inter-individual variability in the susceptibility to these effects to test this assumption. The individual variability was found to be quite substantial for both context effects. As would be expected if a common underlying mechanism contributes to both effects, a significant correlation across observers was found. It is suggested that this putatively common mechanism of 'crispening' accounts completely for the gamut expansion effect, and partially for the simultaneous colour contrast effect, which seems to depend on von Kries adaptation also.
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