S-cone discrimination in the presence of two adapting fields: data and model

Chromatic discriminations along two cardinal axes share a common attentional resource

Attentional modulation is specific to either luminance or chromatic contrast discrimination, implying separate attentional resources for processing luminance and chromatic information processing [e.g., Curr. Biol.12, 1134 (2002)CUBLE20960-982210.1016/S0960-9822(02)00921-1]. However, there are two distinct visual pathways that process chromatic information: the parvocellular (PC) and koniocellular (KC) pathways. It is unclear whether there are separate attentional resources modulating the chromatic processes in these pathways. Here, we examined the attentional modulation effects on chromatic contrast discrimination with chromaticities along the $l$l or $s$s cardinal axis on a cone chromaticity space for preferentially stimulating either the inferred PC or KC pathway, respectively. A dual-task interference paradigm was used, and chromatic contrast discrimination sensitivities under dual-task conditions were compared with that under a single-task condition. The results revealed that compared with the single-task condition, attending to a competing central task in the dual-task condition decreased the peripheral discrimination sensitivity in both chromatic cardinal axes, and sensitivity reduced regardless of whether the dual tasks were along the same or different chromatic cardinal axes. These findings indicate that attentional effects on chromatic processes are not specific to the cardinal axis, suggesting that the PC and KC pathways may share a common attention resource in modulating chromatic processing.

Dissociation of equilibrium points for color-discrimination and color-appearance mechanisms in incomplete chromatic adaptation

We compared the color-discrimination thresholds and supra-threshold color differences (STCDs) obtained in complete chromatic adaptation (gray) and incomplete chromatic adaptation (red). The color-difference profiles were examined by evaluating the perceptual distances between various color pairs using maximum likelihood difference scaling. In the gray condition, the chromaticities corresponding with the smallest threshold and the largest color difference were almost identical. In contrast, in the red condition, they were dissociated. The peaks of the sensitivity functions derived from the color-discrimination thresholds and STCDs along the L-M axis were systematically different between the adaptation conditions. These results suggest that the color signals involved in color discrimination and STCD tasks are controlled by separate mechanisms with different characteristic properties.

Contributions of rhodopsin, cone opsins, and melanopsin to postreceptoral pathways inferred from natural image statistics

Visual neural representation is constrained by the statistical properties of the environment. Prior analysis of cone pigment excitations for natural images revealed three principal components corresponding to the major retinogeniculate pathways identified by anatomical and physiological studies in primates. Here, principal component analyses were conducted on the excitations of rhodopsin, cone opsins, and melanopsin for nine hyperspectral images under 21 natural illuminants. The results suggested that rhodopsin and melanopsin may contribute to the three major retinogeniculate pathways. Rhodopsin and melanopsin may provide additional constraints in natural scene statistics, leading to new components that cannot be revealed by analysis based on cone opsin excitations only.