Spatial-frequency response of a photoreceptor and its wavelength dependence I Coherent sources

The response of an isolated model foveal cone to a coherent sinusoidal intensity source is explored with use of the methods of photoreceptor optics. The dielectric waveguide model of a foveal cone that was previously used to explain the Stiles-Crawford effect and its wavelength dependence [Vision Res. 13, 1115 (1973)] is applied to photoreceptor excitation by coherent gratings with variable spatial frequency and light wavelength. The results indicate that the photoreceptors themselves contribute to visual acuity through a wavelength-dependent response at each spatial frequency. In particular, the isolated photoreceptor has a characteristic low-pass spatial-frequency-filter effect for wavelengths between 410 and 654 nm (where two waveguide modes are carried) and a flat response for wavelengths greater than 654 nm (the single-mode region).