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Keiji Uchikawa, Chizuru Nakajima, Kaori Segawa; Categorical color constancy for dichromats. Journal of Vision 2005;5(8):272. doi: 10.1167/5.8.272.
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It was reported that dichromats showed categorical color perception similar to that of normal trichromats under a white illuminant, which suggested rod contribution to the chromatic mechanisms, along with lightness cues, to categorize surface colors (Montag and Boynton, 1987, Vision Res., 27, 2153–2162). In the present study we tested whether dichromats could have categorical color perception under various chromatic illuminants in a manner resembling normal trichromats in order to investigate color constancy mechanism. We employed the categorical color naming method using the Berlin-Kay 11 basic color terms (red, green, yellow, blue, brown, purple, orange, pink, gray, white, and black), and the 424 OSA uniform color chips as stimuli. A liquid crystal projector (LCP) illuminated both the test color chip (2.7deg) and its large surrounding gray with illuminance of about 500lx. Test illuminants were Blue (LCP single blue light), 25000K, 6500K (white illuminant), 3000K and Red (LCP single red light). The observer saw the test color chip, one at a time, under a test illuminant. The observer adapted for 3 minutes to the test illuminant before starting a session. Dichromats and normal trichromats participated in this experiment. We found that categorical color regions of the dichromats are surprisingly similar to those of the normal trichromats under all chromatic illuminants. The dichromats used all categorical color names, and the centroids of their color categories spread also along the r/g direction in the OSA color space. Since rod is less sensitive for longer wavelengths it is likely that the dichromats could utilize only lightness cues under the Red illuminant (peak wavelength: 600nm) to categorize colors. This suggests that, for normal trichromats, lightness of surface colors might be a critical cue in categorical color constancy.
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