Representation of Perceptual Color Space in Macaque Posterior Inferior Temporal Cortex (the V4 Complex)

Abstract

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).

Color naming across languages reflects color use

“…The relatively low surprisal of red and yellow, compared with the higher surprisal of blue and green, recalls the smaller individual differences in unique hue settings for red and yellow compared with blue and green (21). These results add to a growing body of research suggesting that the unique hues might not be as special as widely thought (6,22,23). Instead, the results suggest that warm colors (reds, yellows) are associated with higher communicative efficiency compared with cool colors (blues, greens).…”

“…Cross-cultural studies of color naming appear to indicate that color categories are universal (1)(2)(3). However, the variability in color category boundaries among languages (4), and the lack of consensus of the forces that drive purported universal color categories (5,6), promotes the idea that color categories are not universal, but shaped by culture (7). Here, we focus on two color categories, WARM and COOL, which are not part of the canonical set of "basic" categories proposed by Berlin and Kay but which nonetheless may be fundamental (8,9), and which might relate to the basic white/black categories occupying the first stage in the Berlin/Kay hierarchy.…”

Multiplicative modulations in hue-selective cells enhance unique hue representation

“…This figure clearly demonstrates that the majority of LGN, V1, and single-opponent V2 cells (5 out of 6 neuron types) peak close to cone-opponent axes. In contrast, our model multiplicative V2 cells and hue-sensitive V4 neurons peak at both cone-opponent and intermediate hues, as reported in [35] and [19]. In other words, with an increase in nonlinearity, representation of hues along intermediate directions start to develop.…”

“…Following these observations, Li et al [15] suggested that different multi-patch patterns represent different hues, and such a distributed and combinatorial color representation could encode the large space of physical colors, given the limited number of neurons in each cortical color map. Other studies also suggested that glob populations uniformly represent color space [19] with narrow tunings for glob cells [19,20,21].…”

Build-up of serial dependence in color working memory

“…The fact that serial dependence is similar for color and spatial working memory thus suggests that it depends on inter-trial interferences that occur at processing stages with representational maps equally distant from the corresponding perceptual map, and this points at higher color processing stages. A candidate region for this is the inferotemporal (IT) cortex, where continuous neuronal representations of color of circular shape on the two perceptual cardinal axes (yellowish-bluish and greenish-reddish axis) have been found 43,44 .…”