Temporal sensitivity of macaque ganglion cells to lights of different chromaticity

Three psychophysical paradigms have shown that moderately high retinal illu minance (ca. 1000 rd) long-wavelength chromatic adaptation results in a dis proportionate reduction in visual sensitivity to rapidly modulated lights. (i) Critical-flicker-fusion - log retinal illuminance (CFF-log I) functions are shallower for long-wavelength than middle-wavelength modulated lights. (ii) A long-wavelength light modulated just above CFF appears as flickerin g ifa steady middle-wavelength pedestal is added (iii) The R/C ratio for he terochromatic modulation photometric (HMP) equality increases with light le vel when the mean chromaticity is approximate to 605 nm, but not when it is approximate to 570 nm. The goal was to evaluate whether Magnocellular - (M C-) pathway retinal ganglion cells show reduced modulation sensitivity with long-wavelength adaptation, as is observed with these three psychophysical paradigms. In Experiment (I), CFFs for 554 and 638 nm lights were estimate d by noting the temporal frequencies at which the cells firing fell below 1 0 imp/s. CFF was measured for light levels between 1-1000 td. Seventeen of 17 units showed a higher CFF at 1000 td for 554 nm, consistent with psychop hysical observation. In Experiment (2), a steady 1000 td 554 nm pedestal wa s added to a 1000 td 638 nm modulated light. Four of 6 units showed higher 638 nm CFF when the steady 554 nm pedestal was present. In Experiment (3), Heterochromatic Modulation Photometry responsivities were obtained at 200 a nd 2000 td as a function of the relative modulation of 554 and 638 nm count erphase lights. Chromaticity was metameric to either 605 or 570 nm. Fifteen of 17 units showed substantial changes in log (R/G) with luminance for the 605 nm, but not for the 570 nm adaptation condition. Thus, temporal phenom ena observed psychophysically may be seen in MC-pathway cells. The results are interpretable as arising front interactions between signals originating from the L- and M-cone receptor types, not from differences in temporal pr operties of the two-cone types. (C) 2000 John Wiley & Sons, Inc.