Bleached rhodopsin and retinal interaction.

1. The human rod retina exhibits lateral inhibition which is demonstrated by the sensitization, i.e. improvement in incremental threshold sensitivity, of a steadily illuminated patch of retina when its surround is also illuminated.2. Experiments were carried out to test whether the previously reported equivalence between steady illumination (real light) and signals from bleached rhodopsin (dark light) also carries over into lateral interaction.3. Symmetrical experiments involving real light patches surrounded by dark-light annuli, dark-light patches surrounded by real-light annuli, and dark-light patches surrounded by dark-light annuli showed that dark light is neither susceptible to sensitization by lateral interaction nor capable of exerting it.