Figure 3.

Output Nonlinearities for Two Example Units Show Gain Rescaling as a Function of Stimulus Contrast

(A) For each unit, we fitted a single linear STRF, then calculated a separate output nonlinearity for each contrast condition. The abscissa denotes the output of the linear STRF, $\mathbf{X}\cdot \mathbf{v}$; the ordinate is the predicted spike rate.

(B) The differences between the nonlinearities were quantified by the linear transform required to convert the high-contrast nonlinearity into each of the medium- and low-contrast nonlinearities. Solid curves show the original sigmoids for the unit shown in (A); dashed lines show the result of the transformation of the high-contrast (red) curve into the low-contrast (blue) and medium-contrast (green) curves. The parameters for the high-to-low transform for this unit were G = 2.9, Δx = 17.6%, Δy = 8.9%; the high-to-medium transform parameters were G = 1.5, Δx = 2.0%, Δy = −0.6%.

(C and D) Nonlinearities for a second example unit; panels equivalent to (A) and (B). Parameters for these transforms were G = 1.5, Δx = −27.6%, Δy = 2.4% (high-to-low) and G = 1.2, Δx = −3.8%, Δy = 8.5% (high-to-medium). See also Figure S2.