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Dynamical Adaptation in Photoreceptors

Figure 5

Response to flashes and steps on light backgrounds of different intensities—comparison of data and DA model predictions.

(A) Experimental responses (left) and DA model predictions (right) for brief flashes of light presented at time 0 on backgrounds of increasing intensity. Data intensities and traces are extracted from Fig. 4 in Ref. [16], where the authors varied flash intensities so as to match peak response among the different background intensities. Model predictions are computed using the corresponding parameter set DN (see Table 2). The dotted curve follows Eq. 8. (B) Experimental responses (left) and DA model predictions (right) for steps of light on three backgrounds of increasing intensity. Data intensities and traces are extracted from Fig. 1 in Ref. [16]. Model predictions are computed using the corresponding parameter set DN (see Table 2). Background light intensity is indicated as in (A). (C) DA model predictions of responses to 100 ms bright (+) and dark (−) flashes equal to the background intensity, delivered at time 0. Flashes are delivered on top of a light background of 2.6·10⁵ photons/µm²/s (, for a comparison with the strength of the non-linearity). (D) Family of peak responses to steps against step intensity. Each curve of the family corresponds to a different background of light; the background intensity increases to the right. The abscissa measures the total light intensity, so the zero crossing of each curve yields the corresponding background intensity. Negative ordinate values (upward segments of the curves) result from light steps, while positive ones (downward segments of the curves) result from dark steps. Data (open circles) are extracted from Fig. 8 in Ref. [18]. DA model predictions (solid lines) use parameter set B (see Table 2). (E) DA model predictions of responses to 10 ms flashes with large contrasts, delivered at time 0, varying from 0.5 to 2¹⁵ times the background intensity by factors of 4; the individual values are listed against the curves. The background light intensity, , was set to . The parameter set B was used to compute the traces in both D and E (see Table 2). (F) Step response sensitivity (normalized by the response in the dark) against background intensity. Data points (open circles) are from Fig. 11 in Ref. [18]. The model prediction (red line) is computed using parameter set B (see Table 2). Both data and model satisfy the Weber-Fechner law over seven decades. (G) Delay (following the input flash) of peak responses to a fixed flash against background light intensity. Data are extracted from Fig. 5A (closed, black circles) and from Fig. 12 in Ref. [15] (open, black circles). DA model predictions use parameter set DN (red circles, see Table 2).

doi: https://doi.org/10.1371/journal.pcbi.1003289.g005