Abstract
Spectral sensitivities of visual systems are specified as the reciprocals of the intensities of light (quantum fluxes) needed at each wavelength to elicit the same criterion amplitude of responses. The review primarily considers the methods that have been developed for electrophysiological determinations of criterion amplitudes of slow-wave responses from single retinal cells. Traditional flash methods can require tedious dark adaptations and may yield erroneous spectral sensitivity curves which are not seen in such modifications as ramp methods. Linear response methods involve interferometry, while constant response methods involve manual or automatic adjustments of continuous illumination to keep response amplitudes constant during spectral scans. In DC or AC computerized constant response methods, feedback to determine intensities at each wavelength is derived from the response amplitudes themselves. Although all but traditional flash methods have greater or lesser abilities to provide on-line determinations of spectral sensitivities, computerized constant response methods are the most satisfactory due to flexibility, speed and maintenance of a constant adaptation level.
Highlights
The physiological study of color vision necessarily requires the determination of spectral sensitivity functions S(λ) of cells of the visual system, beginning with photoreceptors
The spectral sensitivity of a photoreceptor depends on the absorption spectrum of its photopigment
The determination of a spectral sensitivity function involves determining the number of quanta per second at each wavelength that must fall upon a photoreceptor to evoke an equal contribution towards vision1
Summary
The physiological study of color vision necessarily requires the determination of spectral sensitivity functions S(λ) of cells of the visual system, beginning with photoreceptors. According to the Principle of Univariance [1], “...every quantum that is effectively absorbed makes an equal contribution towards vision”, independent of the wavelength of the absorbed light. This is not to say that all wavelengths are absorbed; they most assuredly are not. The determination of a spectral sensitivity function involves determining the number of quanta per second at each wavelength that must fall upon a photoreceptor (how intense a light must be at each wavelength) to evoke an equal contribution towards vision. B wavelengths are considered to make an equal contribution towards vision when they elicit the same magnitude of electrical response. The electrical responses considered in this review will be graded receptor (non-spiking) potentials recorded intracellularly from photoreceptors and other visual neurons, but optic nerve discharges and electroretinograms (ERGs) will be considered
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