The effects of colour adaptation and stimulus size on white perception as a function of eccentricity in man.

We studied how much desaturating complementary colour had to be added to blue, green or red after homochromatic adaptation of short duration in order to perceive white or grey at eccentricities of 0-15 deg in the nasal visual field. The CIE 1931 (x,y) chromaticity coordinates corresponding to achromatic perception were subtracted from the chromaticity coordinates of blue, green and red in order to obtain the threshold differences (dx, dy) in chromaticity coordinates. When the stimulus size was constant at all visual field locations, the absolute values of dx and dy decreased with increasing eccentricity, which means that the desaturation threshold for white or grey perception was higher at the fovea than in the periphery. However, when the stimulus size was M-scaled magnifying its size with increasing eccentricity in inverse proportion to the lowest local sampling density of the human retina (cones and ganglion cells at eccentricities 0-10 and above 10 deg, respectively), dx and dy with blue became independent of visual field location except for the very centre of the fovea. However, M-scaling was unsuccessful with green and red. Although M-scaling with green reduced the change in dx and dy as a function of eccentricity, it had no effect on dx and dy with red colour.