Black-white and pattern discrimination in rats without photoreceptors

Abstract

The discrimination performance of rats whose retinas lacked receptor cells was compared with the performance of normal, control rats. Retinal degeneration was produced by exposing animals to 30 days of constant light at 18 ft-c intensity. Both control rats and those with retinal degeneration were trained and tested in a T-maze on a black-white discrimination and two pattern discriminations. In the pattern tasks, the discriminanda consisted of targets with alternating black-and-white stripes oriented either horizontally or vertically. In the easier pattern discrimination the black-and-white stripes were 0.8 cm wide and in the more difficult pattern task they were 0.4 cm wide. The general finding was that rats without receptor cells were not impaired on any of the discrimination tests used in this experiment, but could readily perform at high levels on both black-white and pattern tasks. They could not only retain a visual habit learned prior to the degeneration, but could learn new discriminations at rates indistinguishable from control animals. The results strongly suggest that retinal elements other than receptor cells are sensitive to light.