The visual system can segregate a figure from the background by grouping similar colors. Chromatic characteristics of figure segregation have not been fully investigated as compared with those of uniform color discrimination. In this study, we investigated differences in chromatic characteristics between figure segregation and color discrimination. The stimulus was a multi-colored texture composed of random shape pieces. It was divided into two regions, the test region and the background region. The chromaticities of the test and background regions distributed on isoluminant lines, which started at the origin in the DKL color space. These isoluminant lines varied in hue direction. The chromaticity distributions of the test and the background regions were the same in saturation. We measured hue difference thresholds between the test and background regions for figure segregation and for color discrimination. In threshold measurement for figure segregation, the observer judged whether two test region figures were identical. In the results, both thresholds of figure segregation and color discrimination for all color directions increased as the saturation distribution increased. These results suggest that figure segregation and color discrimination were not conducted performed by the cone-opponent mechanisms. Properties in hue difference for figure segregation and color discrimination thresholds were found different in the similar manner between observers. These hue property differences imply that there exist some factors effective in hue in a certain level from color discrimination to figure segregation.

Among the many neuroimaging tools available for studying human brain functions, functional magnetic resonance imaging (fMRI) is the most widely used today. One advantage of fMRI over other imaging techniques is its relatively high spatial resolution. High-resolution fMRI, with its superb signal-to-noise ratio and improved tissue-vessel specificity, has strengthened the capability of fMRI and allowed mapping of fine cortical architectures in the human brain. In this presentation, I will first explain the factors limiting the spatial specificity of the blood oxygenation level-dependent (BOLD) effect, based on which most of fMRI experiments are conducted, and the measures dealing with these factors. I will then introduce several highresolution (sub-millimeter) studies on the functional organization of human primary visual cortex (V1), including mapping of ocular dominance columns, mapping of temporal frequency dependent domains and direct demonstration of tuning to stimulus orientation. Finally, I will present some recent results from highresolution studies revealing orientation specific responses in large draining veins, a finding closely related to the interpretation as why conventional low-resolution (～3mm) fMRI signals can be reliably used to decode stimulus orientations.