Figure 10.

A, B, The variance of response to 10 repetitions of each natural image fragment is plotted against the mean response to that fragment for the two neurons illustrated in Figures 4, A and B, and 5, A and B, and E and F. Data with mean response of zero cannot be plotted on the log–log axes; there are fewer data plotted in A because the responses of this neuron were sparser than the responses of B (Figs. 4A,B, 5A,B). The lines are the lines of equality. Regression lines fitted to those points with abscissa value 0.4 and above had slope and intercept: 0.951, 1.238 (A), and 0.707, 0.783 (B). The intercept is the average ratio of variance to mean response for that neuron. C, For 24 neurons, the average variance/mean-response ratio was calculated for those flashed natural image stimuli giving a mean response of at least 0.4 action potentials per presentation and is plotted as ordinate against the variance/mean-response ratio for moving high contrast sinusoidal gratings. The ratio for natural image stimuli was calculated from 10 repetitions of up to 500 stimuli; the ratio for gratings was calculated for 30 cycles of up to 12 stimuli, varying in spatial frequency or orientation. The line is the line of equality.