We tested whether motion and configural complexity affect perceived transparency. A series of five coherent chromatic transformations in color space was applied across a figure: translation, convergence, shear, divergence and rotation. The stimuli consisted of a bipartite or a checkerboard configuration (10 x 10 degrees), with a central static or moving overlay (5 x 5 degrees). Three different luminance conditions (the plane of chromatic transformation oriented toward higher, lower, or equal luminances) were also tested for each of three modulation depths. For each stimulus, the observer judged whether the overlay appeared transparent or not. The main results indicated an interaction between the type of chromatic transformation and stimulus motion and complexity. For example, convergences are judged to appear transparent significantly more often when motion is added for bipartite configurations, or when they are generated in a checkerboard configuration. Surprisingly, shears that have been reported to appear opaque, are more frequently reported to appear transparent with short vector lengths and when combined with motion. Other transformations are also affected by motion, although the effectiveness of figural complexity on transparency seems to depend on both the type of color shifts and the presence of motion. The results indicate that adding motion and stimulus complexity are not necessarily neutral with respect to the chromatic shifts evoking transparency. Thus, studies that have used motion to enhance transparency may yield different results about the color shifts supporting transparency perception from those that did not. The same might be supposed for stimulus complexity under some conditions.
One example of color constancy is color transparency: when a surface is seen both in plain view and through a transparent overlay, the visual system still identifies it as a single surface. Previous studies suggest that color changes across a region of an image that can be described as translations and/or convergences in a linear trichromatic color space lead to the perception of transparency, but other transformations, such as shear and rotation, do not. Recently, other studies have added motion to their stimuli, claiming that this enhances the transparency effect.We tested whether complex configurations and motion are neutral with respect to the effects of systematic color changes. We defined several experimental conditions: a static versus moving stimulus condition, a simple (bipartite stimuli) versus a more complex configuration (checkerboard stimuli), equiluminant, filter and illumination overlay conditions. Different absolute color changes (vector lengths) were also chosen and varied systematically within the gamut of the monitor.The main results show that motion influences observers' responses for translations independently of stimulus complexity, luminance conditions, and vector lengths. A strong effect is observed for divergences that induce transparency perception in moving checkerboard conditions. However, while shears in a moving bipartite configuration tend to be transparent, this effect is completely cancelled for checkerboard like stimuli, even in motion. Finally, neither motion nor complex configuration effects have been found for convergences.
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