Rod-/L-cone and rod-/M-cone interactions in electroretinograms at different temporal frequencies

We recorded electroretinograms (ERGs) under stimulus conditions that only modulated one cone type: either the L- or the M-cones. In these conditions the rods were also modulated. We measured the ERG responses at different temporal frequencies. A simple model that assumes that the first harmonic components of the responses are the result of a vector addition of rod- and cone-driven ERG responses can explain the data satisfactorily for temporal frequencies at and above 6 Hz. From fits of the model to the data, estimates of the gains and phases of the rod -and cone-driven responses can be obtained. At 6 Hz, the fundamental responses originate exclusively in the rods. The gains of the cone-driven responses are substantial at the other temporal frequencies, are maximal at 12 or 18 Hz, and then decrease with increasing temporal frequencies. The gains of the rod-driven responses decrease more steeply with increasing temporal frequencies than the cone gains. Furthermore, the rod and cone phases decrease approximately linearly with temporal frequency, suggesting that they are mainly determined by a response delay. The response delay in the rod-driven ERGs is larger than in the cone-driven ERGs.