Figure 4. Comparison of response variance V_k at constant response size under RG (abscissa) and LUM (ordinate) conditions for the DC response (f₀), left column, and the fundamental Fourier component (f₁), right column.

The response size chosen for comparison is the midpoint of the range of overlap of the RG and LUM response amplitudes. Top row, all dichromat neurons. Second row, non-opponent neurons from all trichromats. Third row, opponent neurons from Δ13 trichromats. Fourth row: opponent neurons from Δ20 trichromats. For f₁ responses in Δ20 trichromats, there is a larger variance under LUM than RG conditions. There is a trend in the opposite direction for the other cell types. Variances plotted are V₀ and V₁, as defined by eqn (3) and interpolated by eqn (5), at constant response size. Error bars represent 95% confidence limits on the variance estimates for each neuron, and include the uncertainty of the variance estimates and the model error of the empirical variance versus mean relationship, eqn (5).