Twelve students (Mean age = 23.7 years, SD = 4.4, 7 female) from the University of Aix-Marseille completed experiment 1 and were paid 10 €/h. They were naive with respect to the purpose of the experiment and reported to have normal or corrected-to-normal vision and normal color vision. This experiment

was approved by the ethical committee of the Aix-Marseille University, and by the “Comité de Protection des Personnes Sud Méditerrannée 1” (approval n° 1041). Participants gave their informed written consent according to the declaration of Helsinki. Subjects were tested individually in a dark room (∼0.08 cd/m2). They were seated in a comfortable chair 150 cm in front of a CRT color monitor with a refresh rate of 100 Hz. At this distance, 1 cm on the screen corresponded to approximately 0.38° of visual angle. Stimulus presentation and collection of data were controlled by Psychopy (Peirce, 2007). Special attention was Gamma-secretase inhibitor INCB018424 order paid to the manner in which Psychopy utilizes the vertical refresh rate/sync of the monitor to ensure RT data was not influenced by the vertical blank interval. Stimuli were red and blue circles (radius = 0.24°) presented on the horizontal midline of a 12.18° × 9.15° black field. On every trial, a target circle appeared in the center of the field and was flanked by two circles at an eccentricity of 0.8°

center to center. We manipulated the color saturation of target circles while keeping their luminance constant. To obtain identical levels of perceptual saturation between red and blue, we used the CIE Lightness Chroma Hue device-independent 3 colorimetric space ( IKBKE Commission Internationale de l’Eclairage, 1976), which is a variant of the CIE L*a*b* space specifically designed to accurately map color perception. Chroma quantifies the degree of perceptual saturation across colors. Lightness is a non-linear transformation of luminance. Although the two concepts are different, it is always true that colors with the same lightness will have the same luminance. Six suprathreshold chroma levels (15%, 25%, 35%, 45%, 60%, and 80%) were chosen to span

a large range of color intensities. Red (Hue = 30°) and blue (Hue = 280°) colors always had the same lightness (L = 51), corresponding to a luminance of approximately 19 cd/m2. The chroma level of the flankers was set to 80%, and was never modulated. Colors were calibrated by means of a Brontes colorimeter (Admesy B.V., The Netherlands). Responses were made by the subject pressing either a right or a left button with the corresponding thumb. Button closures were transmitted through the parallel port of the computer to reach high temporal precision. Buttons were arranged on the top of two plastic cylinders (3 cm in diameter, 7 cm in height) serving as handgrips, and the distance between the cylinders was 20 cm. Subjects performed 24 blocks of 96 trials in a single-session experiment lasting approximately 100 min.