Flicker ERG responses to stimuli parametrically modulated in color space

PURPOSE. TO develop methods for recording human electroretinogram (ERG) res ponses to stimuli that modulate different classes of cones in various ratio s, to draw inferences about the combination of cone signals in early retina l processing. METHODS. Subjects viewed large-field temporal modulations presented on a co mputer-controlled color monitor. A flicker photometric paradigm was used to equate the ERG response elicited by interleaved reference and test modulat ions. Test modulations were chosen to stimulate the L- and M-cones in vario us ratios. Results were obtained from color-normal subjects, dichromats, an d an anomalous trichromat. RESULTS. Reliable signals were obtained from all subjects to both L- and M- cone-isolating modulations and to intermediate modulations. Signals from co lor-defective subjects were predominantly determined by the modulation seen by only one cone type, whereas signals from color-normal subjects were sen sitive to both L- and M-cone modulations. For most color-normal subjects, t he recorded signal was a linear function of the contrasts seen by the L- an d M-cones. There was individual variability in how strongly each cone type contributed to the overall signal. CONCLUSIONS. It is straightforward to record signals to color modulations p resented on a CRT by using the flicker photometric ERG. For most observers, signals from L- and M-cones combine linearly. The relative contribution of the two cone: classes varies across observers, probably because of individ ual differences in the relative numbers of L- and M-cones.