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Dynamical Adaptation in Photoreceptors
Figure 10
Behavior of the DA model for different parameter values.
(A) and (B) Families of responses to a flash in different light backgrounds. We use the BHL parameter set as default parameter set, with changes in 
and 
as indicated. The flash intensities take the values 
, 
, 
, 
, 
, with the background light intensities ranging from 
to 
by factors of 10, respectively. (A) and (B) represent identical curves; traces were normalized by their peak values in (B) so that shapes can be compared. As 
increases from 
to 
, the shape of the saturated curves remain unchanged, but the onset of the non-linearity and the amplitude of the curve are affected. As 
increases, the second, overshoot lobe becomes shallow, and hence more difficult to observe (especially in the potential presence of noise). (C) Comparison of the three sets of model parameters used to fit data. Responses to a flash superimposed upon a light background are displayed for different background intensities. In each panel, the five curves correspond to background intensities increasing from from 
to 
by factors of 10; the associated flashes occur at time 0, last for 1 ms, and have unit Weber contrast, i.e., have equal intensity to that of the background. We note that the value of gamma in the BHL panel is higher than in other panels likely because it was fit only to flash responses in the dark, so that amplitude shifts at high background were not included in the fitted data. (D) DA model responses to a weak flash against a dim background (green, 
), a weak flash against a bright background (red, 
), and an intense flash against a bright background (blue, 
). Note that, in the presence of a bright background, zero crossings always occur at the same point and, despite the 400-fold difference in flash strength, the intense-flash response is only 5-fold greater than the weak-flash response.
doi: https://doi.org/10.1371/journal.pcbi.1003289.g010