### Figure 6-1

Simulating the expected change in saturation index on a cell-by-cell basis. *A*, The variability of the F1 response. The open circles are trial-by-trial F1 responses plotted in the real plane versus the complex plane. The closed circle is the mean F1. The length of the dashed line is the amplitude response of this cell, and the angle of the dashed line from the origin indicates the phase. The SD across trials is measured from the euclidean distances between the single trials and their average. *B*, *C*, Coefficient of variation as a function of contrast. Each line is the relationship between the CV (SD/mean F1), and the bolder lines are the average CV as a function of contrast per cell class. The dashed line is the fit of a double exponential to these data. *D*, Simulations of different contrast response functions. Each line is a single contrast response function that passes through the points (sampled at the contrasts used in our experiment). The darkness of the line indicates how saturated the cell is. *E*, *F*, Chance-level variations in the saturation index for P and M cells. Each set of points is a single trial, simulated from the mean responses shown in *D* and the empirically derived relationship between contrast and coefficient of variation. Lines through these points show the median and 95% confidence intervals on these data. For each cell class, the significance criterion we selected was the maximum chance-level change in saturation across all degrees of saturation, according to this simulation. Download Figure 6-1, EPS file.