The visual pigments, oil droplets and spectral sensitivity of the pigeon

Abstract

Microspectrophotometer measurements of the oil droplets and visual pigments in the receptors of the pigeon have demonstrated the presence of at least five types of oil droplet and four visual pigments. The oil droplets act as cut-off filters, their wavelengths of 50% transmission varying depending from which area of the retina they come, but lying between 600 and 610, 560 and 570, 470 and 554, 470 and 476 and below 430 nm, and effectively cutting off light below these wavelengths. The rod receptors contain a rhodopsin with λmax 503 nm. The dominant cone visual pigment has λmax 567 nm and is found in both members of the double cone and three types of single cone. Two further types of single cone contain a green-absorbing pigment (λmax about 515 nm) and another type of single cone a blue-absorbing pigment (λmax about 460 nm). From the transmission characteristics of the oil droplets and the absorbance spectra of the cone visual pigments, the effective spectral sensitivities of each cone type has been derived and directly related to the spectral sensitivities of isolated units in the retina and optic tectum and to the overall photopic sensitivity of the pigeon as measured behaviourally and electrophysiologically. © 1977.