Abstract
A four-parameter model of spectral sensitivity curves was developed. Empirical equations were designed for A1- and A2-based visual pigments with the main ?-band maximum absorptions (?max) from 350 nm, near the ultraviolet, up to 635 nm in the far-red part of the spectrum. Subtraction of the ?-band from the full absorbance spectrum left a ??-band? described by a ?max-dependent Gaussian equation. Compatibility of our templates with A1- and A2-based spectra was tested on the electroretinographic (ERG-derived) scotopic action spectra recorded in dogfish shark, eel, Prussian carp and perch. To more precisely estimate the accuracy of our model, we compared it with widely used templates for visual pigments. There was almost no difference between the tested models in fitting the above-mentioned spectral data. One of the advantages of our model is that in the fitting of spectral sensitivity data it uses non-transformed wavelengths and the shape of the curve remains the same for a broad range of ?max values. Compared to multiparameter templates of other authors, our model was designed with fewer (four) parameters, which we believe can bring us closer to understanding the true nature of the absorption curve.
Highlights
Dartnall’s [1] fundamental idea that the absorption spectra of all visible pigments can be described by a simple pattern or a “nomogram” is based on the assumption that all absorbance curves of visible pigments have the same basic shape when the frequency scale (c/α) is applied to the abscissas, and only the wavelength at which the maximum absorption is recorded is changed
The regularity of the intensity-amplitude relation for the b-wave and the iodate unmasked late receptor potential (LRP) for eels and dogfish sharks has been checked by fitting the experimental data with the basic model [19,25]: (7) Vo = Iα / (Iαo + Iα), where Vo is the normalized voltage (V/Vmax) of the ERG signal (b-wave or LRP), Io is the stimulating light intensity corresponding to Vo = 1/2, and the exponent a is a constant
The slope of the intensity-amplitude of the log sigmoid response that determines the response dynamics in our small spotted dogfish shark, eel, Prussian carp and perch preparations, were within the framework of those registered for other animals and other electrophysiological signals [19,25,28]
Summary
Dartnall’s [1] fundamental idea that the absorption spectra of all visible pigments can be described by a simple pattern or a “nomogram” is based on the assumption that all absorbance curves of visible pigments have the same basic shape when the frequency scale (c/α) is applied to the abscissas, and only the wavelength at which the maximum absorption is recorded is changed. When it comes to spectral sensitivity, Dartnall’s findings do not correspond to experimental data obtained for a wider spectrum [2].
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