Avian vision

This thesis is in two parts. The first part is a literature review of the avian retina. The review deals with issues in the literature concerning each type or layer of cells in the retina, as well as problems involving synaptical interactions in the retina. The chapter on oil droplets discusses problems in photopigments and avian colour vision as well. Centrifugal fibres and their possible functions are discussed. The avian pectin and hypotheses about its function are dealt with. Finally the functional and evolutionary significance of the avian retina with regard to the avian visual system as a whole is discussed. The second part concerns experiments on colour preference in the pigeon, with regard to the effects of dark adaptation and intensity of the stimulus. Subjects were rewarded for pecking either a blue or a red key presented simultaneously in various combinations of intensities and under three conditions of light or dark adaptation. It was found that the intensity of the blue stimulus affected the number of pecks to blue in a monotonically increasing function. There was also an interaction between intensity of the blue stimulus and the effects of dark adaptation. The results are discussed in light of motivational factors and rod-cone interactions.