RED-GREEN FLICKER PHOTOMETRY AND NONLINEARITIES IN THE FLICKER ELECTRORETINOGRAM

We investigated whether responses from different cone classes are comb ined before or after the nonlinearity that is responsible for generati ng nonlinear response components of the flicker electroretinogram (ERG ). We measured the nonlinear response of the retina while systematical ly varying the modulation in the long-wavelength-sensitive and middle- wavelength-sensitive cones by changing the proportions of flickering 6 33- and 543-nm lights that compose a sum-of-sinusoids temporal wavefor m. We found that at high temporal frequencies the ERG responses are be st accounted for by a model in which the principal retinal nonlinearit y is located before the convergence of signals from the two cone class es. At low temporal frequencies the ERG signal is dominated by cone-an tagonistic responses. At frequencies of 30 Hz and higher, the flicker ERG and psychophysical flicker photometry give similar estimates of th e relative proportions of long- and middle-wavelength-sensitive cones. The ERG photometric null is frequency dependent, whereas the psychoph ysically determined ratio is much less sensitive to changes in frequen cy.