The retina actively seeks novel features in the visual environment, dynamically adjusting its processing in order to seek the unusual while ignoring the commonplace, say researchers at Harvard University. Their report on the principle of visual novelty detection appears in the journal Nature.
The study’s findings provide evidence that the ultimate goal of the visual system is not simply to construct internally an exact reproduction of the external world. Rather, our optic systems seek to extract the few bits of data that are relevant to behavior from the continuous barrage of raw visual information. The researchers said that this dynamic retinal adaptation provides a means of stripping from the visual stream predictable and therefore less newsworthy signals. “Apparently our thirst for novelty begins in the eye itself,” said Harvard professor Markus Meister. “Our eyes report the visual world to the brain, but not very faithfully. Instead, the retina creates a cartoonist’s sketch of the visual scene, highlighting key features while suppressing the less interesting regions.”
Working with salamanders and rabbits, Meister and his co-researchers recorded neural signals from the animals’ retinal ganglion cells, testing whether adaptation to a different environment altered the encoding of retinal signals. From the neural responses to novel stimuli, the researchers computed the sensitivity of individual ganglion cells to various scenes. For most cells, sensitivity to a novel scene was greater than sensitivity to control scenes to which the animals had already been exposed, a gap that grew gradually in the seconds after introduction to a new environment. As the adaptation occurred in both salamanders and rabbits, Meister concluded that it typifies retinal function in both amphibians and mammals, animals that differ in physiology but share the challenge of adjusting to variable visual environments.