Polarization contrast vision in a vertebrate: Behavioral and anatomical support for the double cone hypothesis
Many species of invertebrates and vertebrates--the latter including amphibians, birds, fish and reptiles--are sensitive to the polarization of light. The biophysical mechanism underlying invertebrate polarization sensitivity is a dichroism intrinsic to ultraviolet-sensitive photoreceptors--the parallel alignment of photopigment molecules along the tangentially-extended microvilli. Such dichroism to axially-propagated light is not typically present in vertebrate photoreceptors, and the mechanism underlying vertebrate polarization sensitivity has not yet been discovered. However, this document reports features of a vertebrate's (the green sunfish, Lepomis cyanellus) sensitivity to polarized light which ascribe the biophysical mechanism to the retinal mosaic of birefringent double (twin) cones. The experiments in this thesis show that the double cone birefringent waveguide hypothesis of vertebrate polarization vision accurately predicts (1) the periodicity, (2) absolute phase, and (3) action spectrum of polarization sensitivity to small visual targets, as well as (4) the detailed local morphological structure of the double cone mosaic at the retinal position of target imaging. Evidence is presented which argues that the retinal mosaic of double cones generates a polarization-opponent neural image, which in turn serves as the basis of a previously-undescribed type of vertebrate vision: polarization contrast. Polarization contrast, being the green sunfish's most sensitive visual mechanism under photopic conditions at long wavelengths, is hypothesized to function as a mechanism for object detection. ^
Cameron, David A, "Polarization contrast vision in a vertebrate: Behavioral and anatomical support for the double cone hypothesis" (1991). Dissertations available from ProQuest. AAI9211915.