Spatial summation and light adaptation in the goldfish visual system

Abstract

IN attempting to explain how visual acuity improves as illumination increases, Pirenne and Denton¹ suggested that the retinal image is sampled by numerous units, each summing the effects of light over a region of the retina. At very low luminances, only units with the largest summation areas are functional, but with increasing luminance smaller units come into play as their thresholds are exceeded. Since that suggestion was made, cells at all levels of the visual system have been studied electrophysiologically and many receptive fields have been described that might form the basis for such units. Goldfish and other cyprinid fishes, have been the subjects of many such studies, and their retinal synaptic connections have been revealed in detail. I report here some psychophysical experiments which show the effects of light adaptation on spatial summation in the goldfish. The results are consistent with the connections made by rods and cones in the cyprinid retina, and with the theory of a progressive recruitment of ganglion cells with smaller receptive field centres as background luminance is raised.