Advances in Color Science: From Retina to Behavior

Abstract

Color has become a premier model system for understanding how information is processed by neural circuits, and for investigating the relationships among genes, neural circuits, and perception. Both the physical stimulus for color and the perceptual output experienced as color are quite well characterized, but the neural mechanisms that underlie the transformation from stimulus to perception are incompletely understood. The past several years have seen important scientific and technical advances that are changing our understanding of these mechanisms. Here, and in the accompanying minisymposium, we review the latest findings and hypotheses regarding color computations in the retina, primary visual cortex, and higher-order visual areas, focusing on non-human primates, a model of human color vision.In trichromatic primates, including humans and Old World monkeys, there are three types of cone photoreceptors that are responsible for color vision ( Fig. 1 A, B). The cone classes are called L, M, and S because of their spectral-sensitivity peaks, which lie in the long-, middle-, and short-wavelength regions of the visible spectrum. These labels replace the misleading terms "red," "green," and "blue." Two physically distinct stimuli appear as different colors only if they produce different relative activations in at least two cone types; conversely, any pair of physically distinct stimuli that activate the cone types in the same relative amount appear the same, like the two yellows shown in Figure 1C. While photoreceptor responses are easily computed from the spectral distribution of the stimulus, there is no straightforward relationship between photoreceptor response and color (Hofer et al., 2005a;Shevell and Kingdom, 2008). The multitude of color phenomena, including color afterimages, color assimilation, neon-color spreading, color constancy, and colored shadows, is compelling because in many cases two physically identical stimuli are made to appear different colors, or two physically different stimuli are made to appear the same simply by changing the spatial or temporal context (Fig. 2). A full description of the neural machinery for color should account for these observations, as well as more cognitive phenomena involving the relationship between experience, language, memory, emotion and color. The neural basis of color has been reviewed previously from a range of perspectives (Gegenfurtner, 2003;Gegenfurtner and Kiper, 2003;Lennie and Movshon, 2005;Sincich and Horton, 2005;Solomon and Lennie, 2007;Conway, 2009;Dobkins, 2009;Jacobs and Nathans, 2009;Stockman and Brainard, 2010). Here we focus on advances and pressing questions regarding the mechanisms of color in retina, striate cortex, and extrastriate cortex of non-human primates, although we note that other species are emerging as excellent model systems of color processing (Lotto and Chittka, 2005;Van Hooser and Nelson, 2006;Osorio and Vorobyev, 2008;Borst, 2009;Johnson et al., 2010;Srinivasan, 2010). Retinal mechanismsA single cone by itself is color blind b...

Psychophysical Chromatic Mechanisms in Macaque Monkey

“…The FF condition might be expected to activate subcortical visual circuits better than the Gr condition because subcortical cells respond poorly to spatial chromatic contrast (Wiesel and Hubel, 1966), although the spatial scale of the Gr stimulus was relatively coarse (0.5 cycle/°) compared with the scale of most LGN receptive fields, and the drift rate (1 Hz) was approximately the same as the temporal modulation of the FF stimulus. However, cortical color circuits would respond much more strongly to the Gr condition than to the FF condition because cortical cells respond well to spatial chromatic structure (Conway et al, 2010). For example V1 double-opponent cells respond to adjacent cone-isolating bars of similar width to the Gr frequency (Conway, 2001;Conway et al, 2002).…”

Improved color constancy in honey bees enabled by parallel visual projections from dorsal ocelli

“…Chromatic adaptation is thus thought unlikely to be the sole mechanism enabling constancy (8,9), and different cortical or other neural processing mechanisms seem important for reliable color vision (10,11). Considering human vision, color processing involves multistage neural representations from V1 to V4 and the frontal cortex, and although V4 neurons seem critical for automatic color constancy operations (11)(12)(13)(14), subsequent neural processing stages have been implicated (15).…”

Categorical encoding of color in the brain

“…Although there is some understanding of the areas of the brain involved in color vision, there is lack of clarity on where color is encoded categorically (14). It has been proposed (15)-but also refuted (16)-that clusters of color-preferring cells ("globs") in macaque posterior inferior temporal (IT) cortex represent the four "unique hues" (red, green, yellow, and blue) that all colors can be described in terms of.…”