Contrast dependence of On parasol responses to full- and split-field stimuli. A, Average inhibitory conductances elicited by full (left, 6.25, 12.5, 25, 50 and 100% contrast) and split (right, 12.5, 25, 50, 100% contrast) field sinusoidal stimuli. B, Average excitatory conductances to the same stimuli as in A. C, Average excitatory conductances and firing rate for 25% contrast full field (left) and 100% contrast split field (right) stimuli. These contrasts elicited similar amplitude excitatory inputs. D, Ratio of peak amplitude of inhibitory input to excitatory input for full- and split-field stimuli. Small dots represent data from individual cells. E, Spike rate duty cycle (see Materials and Methods) plotted against duty cycle for excitatory synaptic inputs. F, Mean firing rate as a function of mean excitatory conductance for full- and split-field stimuli. Error bars in D–F are SEM computed across cells.