The spatial structure of color cell receptive fields is controversial. Here, spots of light that selectively modulate one class of cones (L, M, or S, or loosely red, green, or blue) were flashed in ...and around the receptive fields of V-1 color cells to map the spatial structure of the cone inputs. The maps generated using these cone-isolating stimuli and an eye-position-corrected reverse correlation technique produced four findings. First, the receptive fields were Double-Opponent, an organization of spatial and chromatic opponency critical for color constancy and color contrast. Optimally stimulating both center and surround subregions with adjacent red and green spots excited the cells more than stimulating a single subregion. Second, red-green cells responded in a luminance-invariant way. For example, red-on-center cells were excited equally by a stimulus that increased L-cone activity (appearing bright red) and by a stimulus that decreased M-cone activity (appearing dark red). This implies that the opponency between L and M is balanced and argues that these cells are encoding a single chromatic axis. Third, most color cells responded to stimuli of all orientations and had circularly symmetric receptive fields. Some cells, however, showed a coarse orientation preference. This was reflected in the receptive fields as oriented Double-Opponent subregions. Fourth, red-green cells often responded to S-cone stimuli. Responses to M- and S-cone stimuli usually aligned, suggesting that these cells might be red-cyan. In summary, red-green (or red-cyan) cells, along with blue-yellow and black-white cells, establish three chromatic axes that are sufficient to describe all of color space.
Neural basis for unique hues Stoughton, Cleo M.; Conway, Bevil R.
Current biology,
08/2008, Letnik:
18, Številka:
16
Journal Article
Recenzirano
Odprti dostop
All colors can be described in terms of four non-reducible ‘unique’ hues: red, green, yellow, and blue
1. These four hues are also the most common ‘focal’ colors — the best examples of color terms in ...language
2. The significance of the unique hues has been recognized since at least the 14
th century
3 and is universal
4,5, although there is some individual variation
6,7. Psychophysical linking hypotheses predict an explicit neural representation of unique hues at some stage of the visual system, but no such representation has been described
8. The special status of the unique hues “remains one of the central mysteries of color science”
9. Here we report that a population of recently identified cells in posterior inferior temporal cortex of macaque monkey contains an explicit representation of unique hues.
The lateral geniculate nucleus is thought to represent color using two populations of cone-opponent neurons L vs M; S vs (L + M), which establish the cardinal directions in color space (reddish vs ...cyan; lavender vs lime). How is this representation transformed to bring about color perception? Prior work implicates populations of glob cells in posterior inferior temporal cortex (PIT; the V4 complex), but the correspondence between the neural representation of color in PIT/V4 complex and the organization of perceptual color space is unclear. We compared color-tuning data for populations of glob cells and interglob cells to predictions obtained using models that varied in the color-tuning narrowness of the cells, and the color preference distribution across the populations. Glob cells were best accounted for by simulated neurons that have nonlinear (narrow) tuning and, as a population, represent a color space designed to be perceptually uniform (CIELUV). Multidimensional scaling and representational similarity analyses showed that the color space representations in both glob and interglob populations were correlated with the organization of CIELUV space, but glob cells showed a stronger correlation. Hue could be classified invariant to luminance with high accuracy given glob responses and above-chance accuracy given interglob responses. Luminance could be read out invariant to changes in hue in both populations, but interglob cells tended to prefer stimuli having luminance contrast, regardless of hue, whereas glob cells typically retained hue tuning as luminance contrast was modulated. The combined luminance/hue sensitivity of glob cells is predicted for neurons that can distinguish two colors of the same hue at different luminance levels (orange/brown).
The contribution that different brain areas make to primate color vision, especially in the macaque, is debated. Here we used functional magnetic resonance imaging in the alert macaque, giving a ...whole brain perspective of color processing in the healthy brain. We identified color-biased and luminance-biased activity and color-afterimage activity. Color-biased activity was found in V1, V2, and parts of V4 and not in V3a, MT, or other dorsal stream areas, in which a luminance bias predominated. Color-biased activity and color-afterimage activity were also found in a region on the posterior bank of the superior temporal sulcus. We review anatomical and physiological studies that describe this region, PITd, and postulate that it is distinct from areas V4 and TEO. When taken together with single-unit studies and lesion studies, our results suggest that color depends on a connected ventral-stream pathway involving at least V1, V2, V4, and PITd.
Doing science making art Conway, Bevil R
Trends in cognitive sciences,
06/2012, Letnik:
16, Številka:
6
Journal Article
Recenzirano
Odprti dostop
It is a challenge to balance doing both science and art, but I attempt both because each provides unique insight into perception and cognition, often to mutual benefit. The techniques I use in visual ...neuroscience (psychophysics, fMRI, microelectrode recording) are different from those I use in visual art (etching, watercolor and oil paint, glass and silk), but the process is always empirical, testing hypotheses driven by observation, trial and error, while striving to be creative.
Over 40 years ago, Hubel and Wiesel gave a preliminary report of the first account of cells in monkey cerebral cortex selective for binocular disparity. The cells were located outside of V-1 within a ...region referred to then as "area 18." A full-length manuscript never followed, because the demarcation of the visual areas within this region had not been fully worked out. Here, we provide a full description of the physiological experiments and identify the locations of the recorded neurons using a contemporary atlas generated by functional magnetic resonance imaging; we also perform an independent analysis of the location of the neurons relative to an anatomical landmark (the base of the lunate sulcus) that is often coincident with the border between V-2 and V-3. Disparity-tuned cells resided not only in V-2, the area now synonymous with area 18, but also in V-3 and probably within V-3A. The recordings showed that the disparity-tuned cells were biased for near disparities, tended to prefer vertical orientations, clustered by disparity preference, and often required stimulation of both eyes to elicit responses, features strongly suggesting a role in stereoscopic depth perception.
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