Flicker ERG responses to stimuli parametrically modulated in color space
Investigative Ophthalmology and Visual Science
To develop methods for recording human electroretinogram (ERG) responses to stimuli that modulate different classes of cones in various ratios, to draw inferences about the combination of cone signal in early retinal processing. Subjects viewed large-field temporal modulations presented on a computer-controlled color monitor. A flicker photometric paradigm was used to equate the ERG response elicited by interleaved reference and test modulations. Test modulations were chosen to stimulate the L-
... to stimulate the L- and M-cones in various ratios. Results were obtained from color-normal subjects, dichromats, and an anomalous trichromat. Reliable signals were obtained from all subjects to both L- and M-cone-isolating modulations and to intermediate modulations. Signals from color-defective subjects were predominantly determined by the modulation seen by only one cone type, whereas signals from color-normal subjects were sensitive to both L- and M-cone modulations. For most color-normal subjects, the recorded signal was a linear function of the contrasts seen by the L- and M-cones. There was individual variability in how strongly each cone type contributed to the overall signal. It is straightforward to record signals to color modulations presented 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 individual differences in the relative numbers of L- and M-cones.