| Lotto, B.R., Purves, D. A rationale for the structure of color space Trends in Neuroscience 2002 (25)2:84-88 [html] |
| The colors perceived by humans in response to light stimuli are generally described in terms of four color categories (reds, greens, blues and yellows), the members of which are systematically arrayed around gray. This broadly accepted description of color sensation differs fundamentally from the light that induces it, which is neither 'circular' nor categorical. What, then, accounts for these discrepancies between the structure of color experience and the physical reality that underlies it? We suggest that these differences are based on two related requirements for successful color vision: (1) that spectra be ordered according to their physical similarities and differences; and (2) that this ordering be constrained by the four-color map problem. |
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| Brown, R.O., MacLeod, D.I. Color appearance depends on the variance of surround colors Current Biology 1997 (7)11:844-9 [html] |
| BACKGROUND: The perceived color at each point in a visual scene depends on the relationship between light signals from that point, and light signals from surrounding areas of the scene. In the well known phenomenon of simultaneous color contrast, changing the overall brightness or hue of an object's surround induces a complementary shift in the perceived brightness or hue of the object's color. Color contrast is thought to contribute to color constancy with changes in illumination. RESULTS: We report a new type of simultaneous color contrast, in which changing only the variance (i.e. contrasts and saturations), but not the mean, of colors in a test spot's surround induces a complementary shift in the perceived contrast and saturation of the test spot's color. Objects appear much more vivid and richly colored against low-contrast, gray surrounds than against high-contrast, multicolored surrounds. CONCLUSIONS: Color appearance depends not just on the mean color of the surround, but also on the distribution of surround colors about the mean. This novel form of simultaneous color contrast is inconsistent with a variety of models of color appearance, including those based on sensitivity regulation at the receptor level, and those in which the effects of complex surrounds on color appearance can be reduced to adaptation to the illuminant or induction from a homogeneous 'equivalent surround'. It tends to normalize the gamut of perceived colors in each visual scene and may also contribute to color constancy under viewing conditions that affect contrast. |
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| Sugita, Y. Experience in early infancy is indispensable for color perception Current Biology 2004 (14):1267-1271 [html] |
| Early visual experience is indispensable to shape the maturation of cortical circuits during development. Monocular deprivation in infancy, for instance, leads to an irreversible reduction of visually driven activity in the visual cortex through the deprived eye and a loss of binocular depth perception. It was tested whether or not early experience is also necessary for color perception. Infant monkeys were reared for nearly a year in a separate room where the illumination came from only monochromatic lights. After extensive training, they were able to perform color matching. But, their judgment of color similarity was quite different from that of normal animals. Furthermore, they had severe deficits in color constancy; their color vision was very much wavelength dominated, so they could not compensate for the changes in wavelength composition. These results indicate that early visual experience is also indispensable for normal color perception. |
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| De Valois, R.L., De Valois, K.K., Switkes, E., Mahon, L. Hue scaling of isoluminant and cone-specific lights Vision Research 1997 (37)7:885-97 [html] |
| ing a hue scaling technique, we have examined the appearance of colored spots produced by shifts from white to isoluminant stimuli along various color vectors in order to examine color appearance without the complications of the combined luminance and chromatic stimulation involved in most previous hue scaling studies, which have used flashes of monochromatic light. We also used spots lying along cone-isolating vectors in order to determine what hues would be reported with a change in activation of only single cone types or of only single geniculate opponent-cell types, an issue of direct relevance to any model of color vision. We find that: 1. Unique hues do not correspond either to the change in activation of single cone types or of single geniculate opponent-cell types. This is well known to be the case for yellow and blue, but we find it to be true for red and green as well. 2. These conclusions are not limited to the particular white (Illuminant C) used as an adapting background in most of the experiments. Shifts along the same cone-contrast vectors relative to different backgrounds lead to much the same hue percepts, independent of the starting white used. 3. The shifts of the perceptual colors from the geniculate axes are in the directions, and close to the absolute amounts, predicted by our [De Valois & De Valois (1993). Vision Research, 33, 1053-1065] multi-stage color model in which we postulate that the S-opponent cells are added to or subtracted from the M- and L-opponent cells to form the four perceptual color systems. 4. There are distinct asymmetries with respect to the extent to which various hues within each perceptual opponent system deviate from the geniculate opponent-cell axes. Blue is shifted more from the S-LM axis than is yellow; green is shifted more from the L-M axis than is red. There are also asymmetries in the angular extent of opponent color regions. Blue is seen over a larger range of color vectors than is yellow, and red over a slightly larger range than green. 5. Such asymmetries are not accounted for by any model that treats red-green and yellow-blue each as unitary, mirror-image opponent-color systems. Although red and green are perceptually opponent, the red and green perceptual systems do not appear to be constructed in a mirror-image fashion with respect to input from different cone types or from different geniculate opponent-cell types. The same is true for yellow and blue. |
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| Maloney, L.T. Illuminant cues in surface color perception: tests of three candidate cues Vision Research 2001 (41):2581-2600 [pdf] |
| Many recent computational models of surface color perception presuppose information about illumination in scenes. The models differ primarily in the physical process each makes use of as a cue to the illuminant. We evaluated whether the human visual system makes use of any of three of the following candidate illuminant cues: (1) specular highlight, (2) full surface specularity [Lee, H. C. (1986). Method for computing the scene-illuminant chromaticity from specular highlights. Journal of the Optical Society of America A, 3(10), 1694 1699; D Zmura, M., & Lennie, P. (1986). Mechanisms of color constancy. Journal of the Optical Society of America A, 3(10), 1662 1672], and (3) uniform background. Observers viewed simulated scenes binocularly in a computer-controlled Wheatstone stereoscope. All simulated scenes contained a uniform background plane perpendicular to the observer s line of sight and a small number of specular, colored spheres resting on the uniform background. Scenes were rendered under either standard illuminant D65 or standard illuminant A. Observers adjusted the color of a small, simulated test patch to appear achromatic. In a series of experiments we perturbed the illuminant color signaled by each candidate cue and looked for an influence of the changed cue on achromatic settings. We found that the specular highlight cue had a significant influence, but that the influence was asymmetric: greater when the base illuminant, CIE standard Illuminant A, was perturbed in the direction of Illuminant D65 than vice versa. Neither the full surface specularity cue nor the background cue had any observable influence. The lack of influence of the background cue is likely due to the placement of the test patch in front of the background rather than, as is typical, embedded in the background |
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| Maloney, L.T. Illuminant estimation as cue combination Journal of Vision 2002 (2):493-504 [pdf] |
| This work briefly describes a model for illuminant estimation based on combination of candidate illuminant cues. Many of the research issues concerning cue combination in depth and shape perception translate well to the study of surface color perception. I describe and illustrate a particular experimental approach (perturbation analysis) employed in the study of depth and shape that is useful in determining whether hypothetical illuminant cues are actually used in color vision. |
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| MacLeod, D.I. Influence of Scene Statistics on Colour Constancy Nature 2002 (415):637--640 [pdf] |
| The light reflected from an object depends not only on the surface properties of this object but also on the illuminant. The same is true for the excitations of the photoreceptors, which serve as the basis for the perceived colour. However, our visual system has the ability to perceive constant surface colours despite changes in illumination1. The average chromaticity of the retinal image of a scene depends on the illumination, and thus might be used by the visual system to estimate the illumination and to modulate the correction that subserves colour constancy. But this measure is not sufÆcient: a reddish scene under white light can produce the same mean stimulation as a neutral scene in red light. Higher order scene statistics for example, the correlation between redness and luminance within the image allow these cases to be distinguished. Here we report that the human visual system does exploit such a statistic when estimating the illuminant, and gives it a weight that is statistically appropriate for the natural environment. |
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| MacLeod, D.I. New dimension in color perception Trends in Cognitive Sciences 2003 (7)3:97-99 [html] |
| Colors are generally ordered in three dimensions, with hue and saturation as polar coordinates of a color circle, and brightness as the third dimension. Intuitively, lines of constant hue (but variable saturation) in such a color space should converge on an achromatic point devoid of hue. However, in new experiments by Ekroll et al. using colored patches in colored surrounds, constant hue lines converge not on 'gray' but on the surround color. This paradoxical observation suggests that the standard three-dimensional conception of perceived color is inadequate. |
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| Lotto, B.R., Purves, D. The empirical basis of color perception Consciousness and Cognition 2002 (11):609-629 [html] |
| Rationalizing the perceptual effects of spectral stimuli has been a major challenge in vision science for at least the last 200 years. Here we review evidence that this otherwise puzzling body of phenomenology is generated by an empirical strategy of perception in which the color an observer sees is entirely determined by the probability distribution of the possible sources of the stimulus. The rationale for this strategy in color vision, as in other visual perceptual domains, is the inherent ambiguity of the real-world origins of any spectral stimulus. |
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| Ekroll, V., Faul, F., Niederee, R., Richter, E. The natural center of chromaticity space is not always achromatic: a new look at color induction Proceedings of the National Academy of Sciences USA 2002 (99)20:13352-6 [html] |
| Although current theories of color vision differ in many respects, they all assume the existence of a uniquely defined neutral point in chromaticity space. It generally is assumed that this point satisfies several criteria simultaneously. One of these criteria is that it is perceived as achromatic. A further criterion shared by most theories is the structural assumption that lines in chromaticity space of constant hue converge on the neutral point. The basic assumption that these two criteria coincide is clearly true for isolated spots of light presented in darkness, and it usually is taken for granted that this coincidence generalizes to more complex visual stimuli. Here, we show that this is not the case. Our experiments with infields in chromatic surrounds revealed that the point in chromaticity space that appears gray is clearly different from the point on which lines of constant hue converge. A plausible interpretation of this apparently paradoxical finding in terms of color scission is proposed. |
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