Figure 4.
Changes in firing rate and gain with contrast. A, Peak rate. Each data point represents peak firing rate elicited by stimuli of low contrast (circles, 5%; cross, 10%; asterisk, 20%) as a function of peak rate at high contrast (70%, x-axis). Inset shows median peak firing rate at the four levels of contrast. Error bars extend from the 25th to the 75th percentile of peak firing rates. Firing rate is weaker, on average, at lower contrast. B, Gain changes. Gain is defined as the ratio of firing rate to contrast. Data points compare gain at lower contrasts with gain at high contrast (70%, x-axis). Inset shows median gain at four levels of contrast, with error bars extending from the 25th to the 75th percentile of the gain distribution. Gain is greatest, on average, at low contrast. Graphical conventions as in A. C, Gain changes as a function of stimulus speed. The average gain over all cells is shown for each contrast and stimulus speed. This figure shows that the reduction in firing rate that occurred with a reduction in contrast could be partially described as a multiplicative effect on the gain. This effect, however, was not the same for all speeds.