Figure 10.

Amplitude and phase of 1F and 2F responses of on- and off-center cells (2.5 Hz drifting gratings, 0.2 cpd). (A) Stimulus waveforms for three modulation conditions, modulation of red light alone (R alone), green light alone (G alone) and counterphase condition. (B) Two possible response phases; 2F responses could line up with the peaks of the 1F responses, or be at 90° to this value. (C–D) Responses of on- and off-center MC cells to the three conditions, and to intermediate conditions corresponding to modulation of the L and M cone alone (20 sweeps, 64 bins/sweep). The peaks of the 2F response tend to line up with the peaks of the luminance response. Vertical lines have been drawn in C, D to illustrate this. The on-center cell displays a 2F response to the silent substitution conditions. The 2F response of the off-center cell is of smaller magnitude. E. Amplitude and phase of 1F and 2F components as a function of R/G gun modulation luminance ratio. 2.5 Hz, 20 sweeps. 1F responses go through a minimum close to a ratio of 1, where 2F ratios are maximal. 1F phases go through a reversal close to a ratio of 1. 2F ratios converge to similar values around 1.