Rod-cone color mixture: effect of size and exposure time

Chromaticity coordinates of monochromatic lights were obtained 8 deg extraf oveally at a retinal illumination of 50 photopic td during the cone-plateau period and also with the subject in a dark-adapted state, while size and e xposure time of the test field were varied. Unexpectedly, we found that for the dark-adapted condition the points representing the chromaticity matche s of the spectral lights generally moved away from the achromatic point in the chromaticity diagram when size or exposure time of the test stimulus wa s increased. Furthermore, the chromaticity shift toward the achromatic poin t, obtained between the cone-plateau period and the dark-adapted state (i.e ., with rod intrusion), tended to decrease with these two test parameters. In fact, when size and exposure time bath were at the maximum level investi gated (7 deg, 500 ms), there was no measurable shift in chromaticity with r od intrusion. Our results suggest that the cone system may become progressi vely more effective in suppressing the rod system as an effect of both size and exposure time. (C) 1999 Optical Society of America [S0740-3232(99)0151 1-2].